OPTIMIZING IRRIGATION AND NITROGEN USE WITH STRAW MULCHING IN POTATO (Solanum tuberosum L.)

Thesis

Submitted to the Punjab Agricultural University in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCEin

SOILS(Minor subject: Botany)

By Sukhwinder Singh (L-2008-A-86-M)

Department of Soil Science College of Agriculture PUNJAB AGRICULTURAL UNIVERSITY LUDHIANA - 141 004 2011

CERTIFICATE I This is to certify that the thesis entitled, Optimizing irrigation and nitrogen use with straw mulching in potato (Solanum tuberosum L.) submitted for the degree of Master of Science in the subject of Soils (Minor subject: Botany) of the Punjab Agricultural University, Ludhiana, is a bonafide research work carried out by Mr. Sukhwinder Singh (L-2008-A-86-M) under my supervision and that no part of this thesis has been submitted for any other degree. The assistance and help received during the course of investigation have been fully acknowledged.

___________________________ Major Advisor [Dr. C B Singh] Senior Soil Scientist Department of Soil Science Punjab Agricultural University Ludhiana 141 004 (India).

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CERTIFICATE II

This is to certify that the thesis entitled, Optimizing irrigation and nitrogen use with straw mulching in potato (Solanum tuberosum L.) submitted by Mr. Sukhwinder Singh (L-2008-A-86-M) to the Punjab Agricultural University, Ludhiana, in partial fulfillment of the requirements for the degree of Master of Science in the subject of Soils (Minor subject: Botany) has been approved by Students Advisory Committee along with Head of the Department after an oral examination on the same.

____________________ Head of the Department [Dr C J Singh]

______________ Major Advisor [Dr C B Singh]

________________________ Dean Post-Graduate Studies [Dr Gursharan Singh]

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ACKNOWLEDGEMENT First of all, I bow my head to AKAL PURKH the ALMIGHTY by whose kindness I have been able to clear another chapter of my life. Though the debt of learning cannot be repaid, it is my sovereign privilege to express my gratitude and moral obligation to my esteemed Major Advisor, Dr CB Singh, Senior Soil Scientist, Department of Soil Science for his enlightened, invaluable and inspiring guidance. I shall remain ever indebted for his care and affection during the course of investigation as well as in the preparation of this manuscript. His multifaceted personality and commitment to work motivated and encouraged me to work, even harder and hence developed right attitude not only for my research work but also as a managed human being. I feel elated in expressing thanks to the members of my advisory committee, Dr (Mrs) Nirmal Kaur Sekhon, Senior Plant Physiologist, Department of Soil Science , Dr VK Arora, Senior Soil Physicists, Department of Soil Science, Dr MS Hadda, Professor of Soil Conservation, Deans Nominee, Department of Soil Science for their expert advice and cooperation from time to time in conducting the research work and for making improvements while going through the manuscript. I am highly thankful to the Head of Department of Soil Science for providing necessary facilities required in lab and field work during my whole Masters Programme. In my opinion, God would not be everywhere; therefore, he made loving parents. A formal acknowledgment of my emotions is inadequate to convey the depth of my feelings of gratitude to Grand father S. Gurbachan Singh Dhillon and my loving parents S. Jagtar Singh Dhillon and Sdn. Harmeet Kaur. I am forever indebted to my parents for their understanding, endless patience and encouragement when it was most required and for providing me the means to learn and understand. I cannot weigh my feelings with words for my dearest brothers and my sister for their motivation, encouragement, everlasting love and affection and moral support. I have been fortunate to come across my funny & good friends without whom life would be bleak. I am happy to acknowledge the shadow support and moral upliftment showered upon me by Gurpreet Singh, Arshdeep, Satnam, DVS Kambo, Rupesh Monga, Sandeep Brar and Mander Sidhu. Thanks are due to the supporting field staff, office staff and lab attendants especially Salwinder Singh, Jaipal Singh, Pawan, Ramkishan Uncle, Satish and Raj Aunty for their help during my research work. Last but not the least, I duly acknowledge my sincere thanks to all those who love and care for me. Every name may not be mentioned but none is forgotten.

(Sukhwinder Singh Dhillon)

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Title of the Thesis Name of the student Admission No. Major Subject Minor Subject Name and Designation of Major Advisor Degree to be Awarded Year of award of Degree Total pages in Thesis Name of University

: :

Optimizing irrigation and nitrogen use with straw mulching in potato (Solanum tuberosum L.) Sukhwinder Singh (L-2008-A-86-M)

: : :

Soils Botany Dr C B Singh Senior Soil Scientist

: : : :

M. Sc. 2011 75+ Appendices+ Vita Punjab Agricultural University, Ludhiana, India ABSTRACT

Water and fertilizer are important factors influencing growth, development and tuber yield of potato. Depleting ground water and increasing cost of fertilizers necessitates that these inputs are used efficiently. Straw mulching is likely to enhance tuber yield and conserve irrigation water and fertilizer. A field experiment was conducted at the research farm of the Department of Soil Science, Punjab Agricultural University, Ludhiana on loamy sand soil to optimize irrigation and fertilizer N use of -1 potato with straw mulching. Two rates of rice straw mulch (0 and 6 t ha ) were imposed in the main plots, three irrigation levels based on IW/PAN-E = 1.0, 1.5 and 2.0 in sub plot and four levels of N @ 0, -1 135, 180 and 225 kg ha in sub-sub plot. Results revealed that mulching helped to store 5-22 mm more soil moisture in 0-120 cm profile and the differences were larger in top 15 cm layer. Straw mulch lowered maximum soil temperature at 5 cm depth by 0.4 to 7.3C and raised minimum temperature by 0.4 to 2.9C. Irrigation water input with IW/PAN-E = 2.0, 1.5 and 1.0 was 24, 16 and 12 cm, respectively. Mulching recorded 25per cent improvement in tuber yield. The WUE improved with N rate and it was progressively increased with decrease irrigation water inputs. Mulching also -1 -1 improved irrigation water use efficiency (WUE) by 26.2 kg tuber ha mm . Optimum irrigation for maximum tuber yield was IW/PAN-E =2.0 without mulch and 1.5 with mulch. Tuber yield improved -1 -1 with fertilizer N upto 225 kg ha without mulch but only upto 180 kg N ha in mulched plot. Mulching increase nitrogen use efficiency and it decreased with increasing N rate. Mulching reduced weed infestation and recorded larger size (>50mm) tubers. To conclude, mulching improved tuber yield besides saving irrigation water and fertilizer N.

Keywords: Potato, Straw mulching, Irrigation, WUE, N efficiency, Tuber yield ______________________ Signature of Major Advisor ___________________ Signature of the student

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CONTENTS

Chapter

Topic

Page

I.

INTRODUCTION

1-2

II.

REVIEW OF LITERATURE

3-14

III.

MATERIALS AND METHODS

15-24

IV.

RESULTS AND DISCUSSION

25-62

V.

SUMMARY

63-65

REFERENCES

66-75

APPENDICES

i-v

6

7

Grow potato with straw mulch to save water and N fertilizer

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CHAPTER I INTRODUCTION Potato (Solanum tuberosum L.), a member of the nightshade family (Solanaceae), is a major world food crop and by far the most important vegetable crop in terms of quantities produced and consumed worldwide (FAO 2005). It is cultivated in autumn and spring season in Punjab. It is high-yielding short duration crop that requires large amount of nutrients and frequent irrigation due to its shallow root system. Potato is sensitive to drought (Van Loon 1981). Scheduling irrigation at proper time and stages of plant growth has great significance in improving the yield of the crop (Singh et al 1990). Judicious application of fertilizers in conjunction with proper irrigation is the principal factor affecting the crop yield (Padem and Alan 1992; Gupta 1990; Bandel et al 1980; Thomas et al 1970). Thus, water and fertilizer N are important manageable factors influencing tuber growth, development, quality and yield. The response to fertilizer varies with soil and climatic conditions. Recovery of fertilizer N in potato crop is generally low and most of fertilizer N is lost through denitrification, immobilization or by leaching out of the root zone to eventually meet the ground water. Reduction in losses of water and nitrogen will be helpful for efficient utilization of these costly resources. Therefore, optimization of irrigation water and nitrogen use for obtaining better potato crop at the same time maintaining growth and yield is essential. The water and nitrogen use efficiency in potato under conventional furrow irrigation is low that could be increased with minimizing losses of water. This suggests developing an integrated approach for water and nutrients management. Being a temperate crop, potato growth and yield are mostly affected by higher temperature, especially a mean temperature above 17oC (Mendoza and Estarda1979). As a result, potato is grown in countries where the prevailing mean air temperature is around 15-18oC during the growing season and rainfall or irrigation provides ample water (Caldiz et al 2001). Soil temperature is one of the most crucial edaphic factors that affect potato growth and development. Several factors control soil temperature but only soil cover and soil moisture are subjected to manipulation. Optimum temperatures for potato cultivation are around 20oC for maximum and 15oC for minimum (Borah and Milthorpe 1963). Haverkort (1990) pointed out that potato is best adapted to cool climates such as tropical highlands with mean daily temperatures between 15 and 18oC. Higher temperatures favour foliar development and retard tuber growth. In addition, heat stress leads to a higher number of smaller tubers per plant; lower tuber specific gravity with reduced dry matter content. However, such soil temperatures do not exist under natural conditions throughout the potato growing season in the state of Punjab. Autumn crop of potato is recommended for planting in October when it is not very hot in the plains. But farmers prefer to advance the planting of potato in early September and consequently, early harvested tubers fetch higher price in the market. However, high 9

temperature prevailing at the time of planting causes poor tuber germination. Nearly 20.8 million tonnes of rice straw are produced every year in the state of Punjab. A substantial proportion (81%) of mechanically harvested rice straw is burnt in the field, which is a net loss of nutrients besides causing environmental pollution. This can be diverted to use as mulch. Mulching is known to improve soil hydrothermal regime, check weed growth and thus, improve crop growth, yield and water use efficiency (Barker and Bhowmik 2001; Hundal et al 2002). Locally available mulch material can also be applied on soils to reduce soil moisture loss from the profile. Many researchers studied the beneficial role of mulch to conserve soil moisture and to reduce soil temperature (Kar 2003; Kar and Singh 2004). Lowering of soil temperature favoured tuber growth and produced good quality tubers, but a lower rate of mulch application (2-2.5 t ha-1) was not effective for enhancing tuber yield (Doring et al 2005). Straw mulching lowers maximum soil temperature, reduces evaporation of soil water and thus conserves soil moisture besides checking weed growth (Jalota et al 2001; Kar and Kumar 2007; Sekhon et al 2008 ; Singh et al 2010). On the other hand, mulching may raise minimum soil temperature by preventing heat loss from soil. Use of straw mulch in potato may also alter its optimum irrigation and nitrogen requirement. Since high soil temperature limits potato production in hot climates (Midmore 1984), mulches may enhance production in such climates, particularly in non-irrigated or water scare areas. Mulch helped to retain more heat in the soil during night resulting in higher minimum temperature than un-mulched soil. Mulching also reduced wilt and late blight incidence, but not to the extent needed for profitable farming (Rautaray 2010). About 77 per cent of the water resource is used in agriculture. Annual deficit of water in the state of Punjab is about 12-lakh-hactare meter (Hira and Khera 2000). A report by Punjab State Farmers Commission (Singh 2006) shows that in Punjab, rate of fall in water table was 65 cm Y-1 during 1998-2005. This is attributed mainly due to pumping of ground water. Keeping in view the declining ground water level and availability of surplus rice straw, there is a need to evolve a technique for reducing water use in raising potato crop. The crop could provide an alternative as crop diversification to farmers. However, a fewer studies have been conducted in this region regarding efficient use of water and nitrogen with mulching for potato cultivation. Hence, the present study was undertaken to investigate the problems with following objectives: 1. To study the effect of straw mulch on soil hydrothermal properties. 2. To find out the optimum irrigation water and fertilizer N requirement of potato under straw mulch. 3. To study the interactive effects of mulching, irrigation and fertilizer N levels on water use and yield of potato.

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CHAPTER II REVIEW OF LITERATURE Potato crop yield is determined by several factors such as soil temperature, fertilizer application, rainfall and a number of agronomic practices viz. planting density and crop rotation besides the genetic characters. Soil temperature, soil water and fertilizer are important edaphic factors which influence crop growth. Mulch offers an easy means to modify the moisture regime, soil temperature and availability of fertilizer. The literature concerning the problem is reviewed under the following heads: 2.1 Optimum temperature requirement for potato growth Climate is the prime uncontrolled environmental factor causing huge fluctuations in crop yield from year to year. Potato plant growth and development is greatly influenced by soil temperature in addition to many other environmental factors. Studies conducted by Neilson et al (1961) have revealed that the optimum soil temperature for potato varies with the nutrients applied but the maximum uptake of elements and the yield increase is observed at temperature near 19.4oC and reduces at 26.6oC. Since the onset and early phases of tuber growth are important for the further development of potato, Dam et al (1996) conducted an experiment with two photoperiods (12 or 18 h) and four 12-h day/night temperatures (18/12, 22/16, 26/20, and 30/24oC) to analyze photoperiod and temperature effects on early tuber growth for cultivars Spunta and Desiree. They concluded that low mean temperatures (15-19oC) with a short photoperiod (12 h) were most suitable for early tuber growth. Different genotype responses to temperature and photoperiod on tuber growth were also observed by Snyder and Ewing (1989) using potato cuttings. Dry matter partitioning to tubers generally was highly and significantly correlated with optimum temperature, 15 to 20oC for tuber growth. Potato plants lost their ability to allocate dry matter to tubers at higher temperatures. The optimum soil temperature for initiating tubers ranged from 16 to 19oC. Tuber development declined as soil temperatures rose above 20C and tuber growth practically stopped at soil temperatures above 30oC. The number of tubers set per plant was greater at lower temperatures than at higher temperatures, whereas higher temperatures favor development of large tubers (Western Potato Council, 2003). Hay and Allen (1978) reported that soil temperatures between 15 and 18oC were optimal for tuberization of potato. High soil temperature increased stem elongation, branching, haulm weight, foliage development and root growth but decreased the accumulation of dry matter in tubers, leading to small malformed tuber production (Slater 1968). Potato quality is as important as yield. Specific gravity and dry matter content along with shape of tuber have been considered as an important factor for judging the quality of

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tuber (Shafi 1963). Midmore and Prange (1992) examined the effect of day and night temperatures (33/25oC and 20/10oC) on relative growth rate and dry matter production of various potato cultivars. The highest relative growth rate was obtained at low temperature whereas higher temperature had the opposite effect of producing the lowest net assimilation and relative growth rate. Both number and weight of tubers were markedly reduced by high temperature and produced virtually no tubers. Grewal and Singh (1974) observed that tuber yield during autumn was positively correlated with minimum soil temperature that varied from 7 to 9.4oC. They also observed a significant positive correlation between tuber size and the minimum temperature during autumn season. On the other hand, potato yields were negatively correlated with the maximum soil temperature during spring. Epstein (1966) observed that potato variety Katahdin, which normally produce spherical tubers, produced elongated and pointed tubers at 280 C and also recorded slight increase in specific gravity from 9 to 15oC and then a rapid decline with higher temperature. Kincaid et al (1993) assessed the influence of interaction between water management and soil temperature on potato quality in the Pacific Northwest and observed that the critical period for tuber quality appeared to be from mid-June to mid-July based on measured soil temperature differences. Frequent sprinkler irrigation reduced soil temperatures, along with the incidence of sugar-end tubers. A green house study conducted by Yamaguchi et al (1964) noticed that the optimum soil temperature for tuber formation was between 15.5 - 21.1oC. Shoot emergence was rapid at 21.1-23.8oC and delayed at 10-12.7oC soil temperature. Many stolons were initiated but tuberization was delayed at the lowest soil temperature of 10-12.7oC. 2.2 Effect of irrigation on soil temperature, crop growth and yield 2.2.1 Effect of irrigation on temperature Irrigation moderates soil temperature by increasing evaporative cooling, specific heat of soil and heat flow into soil due to enhanced thermal conductivity. The extent and duration of this effect however, depends upon solar radiation flux, nature and extent of vegetative cover, thermal properties of soil and amount and temperature of irrigation water applied. Dry soil has a specific heat that approximately equals one-fifth of that of water. Hence a given amount of heat from isolation will increase the temperature of a moist soil less than that of a dry soil (Keen 1932). Application of irrigation that maintains a continually moist soil surface is quite effective in cooling the soil (Wharton and Hobart 1931). Smith et al (1931) showed the effect of irrigation on cooling of soil. Under Arizona conditions on the day following irrigation, the temperature at 2.5, 5.0 and 7.5 cm depth was lowered by 4 to 10, 1 to 4 and 0.5 to 20F, respectively. This fact was emphasized by Gregory (1959) suggesting the maintenance of low soil temperature through light but frequent irrigations resulting in lower soil moisture suctions. This practice promoted plant growth and development. Arkhipova (1954) obtained a 12

difference as large as 28oC in maximum temperature of soil surface between the irrigated and the un-irrigated wheat fields during a period of dry winds. The difference reduced to 6-7oC and 4oC at 5 and 20 cm depth, respectively. Dhesi et al (1964) suggested that soil temperature can be maintained at a low level through the application of light but frequent irrigation for better plant growth. Wierenga et al (1971) found that damping effect of an irrigation on soil temperature was large and of short duration in upper soil layers, but small and of longer duration at lower depth. They found that within a few hours after irrigation, temperature at 10 and 30 cm depths dropped by 10.5 and 6.0oC, respectively. The temperature between irrigated and un-irrigated soil at 10 cm depth was reduced to 2.5oC one day after irrigation and was negligible two days after irrigation. Mehta and Prihar (1973) observed an average decrease of 2oC in the maxima soil temperature at 10 cm depth when soil is wetted with 1 cm simulated rain in the summer. Singh and Sandhu (1978) found that the damping effect of irrigation on soil temperature was large and quick particularly in the un-mulched and less frequently irrigated maize when its crop cover was sparse. They reported a temperature decrease of 10 to 3oC in the upper soil layers with irrigation and the effect lasted for 4-6 days. In another study with sugarcane (Sandhu et al 1980) the maximum soil temperature at 10 cm depth in the crop irrigated frequently with IW/PAN-E ratio of 1.0 was about 0 to 6oC lower than that in the crop irrigated with IW/PAN-E ratio of 0.5. 2.2.2 Effect of irrigation on crop growth and yield Water is essential requirement for plants. Thus reduced availability of water to plants is likely to restrict crop growth. As irrigation is a measure to increase water availability to plants and reduce adverse effects of water deficits in crop. On the basis of several years of experiment Steineck (1958) proved that potato is particularly sensitive to faulty irrigation technique. He emphasized that planning of irrigation at higher tensions and withholding water for 2, 4, 6, weeks period induced yields of 78, 58, and 36 per cent, respectively of the yield of highest yielding treatment. Working on the laterite soils of West Bengal, Moolani and Hukkeri (1965) showed that irrigation at lower tension (0.25 to 0.30 atmospheres) increased yield by 6.12 and 34.5 q ha-1 as compared to yield under 0.6 and 0.9 atmosphere soil moisture tensions, respectively. Doorenbos and Kassam (1979) reported that for high yields at a given site, the seasonal water requirements of a potato crop with a phenological cycle varying from 120 to 150 days ranged from 500 to 700 mm, depending on climate. In a field study Sood (1986) observed that during pre-monsoon period. Supplemental irrigation at 0.5 atmosphere moisture tension stimulated growth and increased potato mean yield by 64 q ha-1 under rainfed conditions. Another study by Singh et al (1988) reported that tuber yield of potato variety Kufri chanderamukhi irrigated on the basis of IW/PAN-E ratio of 2.0 was comparable to that irrigated at 0.25 bar soil water tension but saved 12 cm irrigation water, resulting in 20 13

per cent higher irrigation water use efficiency. In field trails, irrigations given at 25, 50 and 70 per cent of available moisture showed significant improvement in potato tuber yield and A grade tuber with irrigation levels (Yadav and Tripathi1972; Sharma et al 1999). Deficient irrigation promoted a reduction of tuber quality and lowered yield due to reduced leaf area and or reduced photosynthesis per unit leaf area (Van Loon 1981). Khera et al (1976) found that as the IW/PAN-E ratio increased from 0.6 to 0.9, the grain yield as well as dry forage yields of maize increased significantly, but declined with further increase in frequency of irrigation. Potato can be sensitive to irrigation less than evapotranspiration that result in soil water deficits. A study in three successive years on silt loam soil in eastern Oregon investigated the effect of water deficit on yield and quality of four potato cultivars grown under four season-long sprinkler irrigation treatments (Shock et al 1998). MacKerron and Jefferies (1986) have shown that increased duration of water stress before tuber initiation reduces tuber set per stem. Perez et al (1961) observed that yield and percent of large size tubers increased by increasing frequency of furrow irrigation. They concluded that available soil moisture at 30 cm depth should not be allowed to fall below 50 per cent of the field capacity. Straw mulching had favorable effects on plant height and yield (Sandhu et al 1980). Cane yield increased by an average of 13.8 per cent with the 1.00 over the 0.50 times pan evaporation. Similarly, yield averaged 13.8 per cent higher with mulch than without mulch. 2.3 Effect of mulch on soil temperature, crop yield and weeds growth Mulching alter hydrothermal regime by conserving water, modifying soil temperature and controls weeds. These effects are reflected on improved yields of field and vegetable crops. However the extent and direction of the mulching effect on soil temperature varies with the types of mulch, its rate and time of application, season and weather conditions, type of soil and nature and extent of crop cover. Depending upon the prevailing conditions, mulch can cool or warm the soil (Jacks et al 1955) and may accelerate or depress plant growth. In order to quantify the effects of organic mulch on soil temperature during the growth of potato, Midmore (1984) reported favorable manipulation of the edaphic environment in early stage of potato crop that led to improved emergence, crop cover and tuber yield. Midmore et al (1986) conducted seven experiments at three contrasting hot tropical sites to evaluate the effect of organic mulch on soil temperature during the growth of the potato crop. Mean maximum and minimum temperatures during the crop seasons ranged from 27 to 30oC and 16 to 21oC respectively. They concluded that daily soil temperature fluctuations at tuber depth were damped by mulch and maximum reduction of daytime soil temperature was recorded immediately following planting, before the crop emerged. Dahiya et al (2007) studied the straw mulching effects on soil temperature of a loess soil during August to September and reported that the application of wheat straw mulch reduced average 14

soil temperature by 0.74, 0.66, 0.58oC at 5, 15 and 30 cm depth respectively as compared with the control. Rathore et al (1998) reported that soil temperature with straw mulch in chick pea was 0.8 to 3oC lower than in un-mulched plots during December to January. Grewal and Singh (1974) observed that mulches like mat (Typha sp. Interwoven into a web) and pennisitum stalks lower the soil temperature maxima at a depth of 10 cm by 1.5 oC during autumn and by 3.5oC during spring on sandy loam soil. During autumn, potato yields were 35 and 25 per cent higher under mat and pennisitum stalks, respectively as compared with the control. Vadi et al (2005) conducted a field experiment on clay soil and reported that wheat straw mulch @ 6 t ha-1 and ground nut shell mulch @10 t ha-1 were found equally effective and produce more plant height, spread as well as grain and straw yield of pigeon pea as compared with control. However during spring season, the effect of these treatments was more pronounced and yield improvement was 53 and 49 per cent. Kar and Kumar (2007) recorded that use of straw mulch @ 6 t ha-1 in potato registered 3.7 t ha-1 higher tuber yield against 11.2 t ha-1 in no mulch treatment. This improvement was due to reduction in soil temperature by 4-6oC and conservation of soil moisture. Sekhon et al (2005) conducted an experiment on loamy sand soil to evaluate the effect of wheat straw mulch on soil temperature, crop growth and seed yield of soybean. Maximum soil temperatures at sowing depth, recorded during the month of June after sowing were high under no-mulch, ranging from 30.6 to 48.6oC while mulching reduced soil temperature by 1.4 to 12.7oC. Mulching increased soybean seed yield by 4.4 to 68.3 per cent in different cropping seasons; it also increased plant biomass by 17 to 122 per cent and nodule mass by 8 to 220 per cent. Field experiment was conducted by Rautaray (2010) to study the effect of mulching on potato in a rainfed rice-potato cropping system. Potato crop grown after rice recorded 1829 per cent higher tuber yield. The proportion of larger size tuber yield increased by 9 per cent under mulching. In second experiment, mulching with dried water hyacinth improved tuber yield of potato by 3.02 t ha-1 from 11.36 t ha-1 and the proportion of large sized tuber yield was higher (60%) under mulching as compared to control. Sood (1986) observed that application of 42 q ha-1 pine-needle mulch increased potato yield by 64 q ha-1 as compared with conventional rain fed practice. Mahmood et al (2002) reported that mulching decreased daily maximum soil temperature at 15 cm depth by 1.5 to 4.5oC, resulting in faster emergence, earlier canopy development and higher tuber yields. Other studies conducted in Asia point out the beneficial effects of mulch in potato production systems as an efficient alternative to obviate heat and water stresses in order to maximize crop yield (Jaiswal1995; Ruiz et al 1999; Sarma and Dutt 1999).The effect of wheat straw mulch on the performance of field-grown soybean Bragg was studied on a well-drained sandy-loam soil by Kaul and Sekhon (1975) and found that mulch had a great effect on reducing the maximum soil temperature, especially when the 15

prevailing air temperatures were quite high, and also helped in preventing crust formation caused by rainfall. The plant population was 104 per cent more in the mulched treatment that resulted in significant increase in seed yield. Sidhu et al 2007 studied the effect of wheat straw mulch @ 0 and 6 t ha-1 and planting methods (flat and channel) on maize grown for four years on sandy loam soil. They observed that maximum soil temperature without mulch ranged from 32.2 - 44.4oC in channel and 31.6 - 46.4oC in flat planting method. Mulching, however, lowered soil temperature by 0.8 - 7.0oC in channel and 0-9.8oC in flat planting. Mulching improved grain yield by 0.24 t ha -1 and biomass by 1.57 t ha-1. In a field study with summer mung bean on a loamy sand soil, Sandhu et al (1992) reported that application of rice straw mulch @ 6 t ha-1 improved edaphic environment of the root zone through soil water conservation and substantial reduction in maximum soil temperature caused 38 per cent increase in seed yield. Mulches prevent soil water evaporation retaining soil moisture. Jamil et al (2005) studied the effect of types of mulch (plastic, straw, sawdust and control) and their duration (one month and whole season) on growth and yield of garlic. They observed that straw and plastic mulches increase the bulb yield irrespective of their duration. Straw mulch is recommended for garlic production based on overall performance than the others and also being cheaper and organic in nature. Under the Punjab conditions, Dhesi et al (1964) concluded that mats prepared from locally available Sarkanda, and placed on the ridges of the potato lowered soil temperature by 5.9oC as compared to control. These mats kept the soil temperature more or less constant at 6 cm depth for one to four days after irrigation. Total as well as early potato germination was higher under sarkanda cover as compared to other treatments. They advocated the use of sarkanda mats for getting quick germination of potato tubers. Wang et al (2009) conducted field experiments to determine the effect of plastic mulch on soil temperature, potato (S. tuberosum L.) growth and evapotranspiration under drip irrigation and reported 2-9oC higher daily mean soil temperature under mulch than without mulch, especially during the early stages. Potato growth was restrained under mulching in the North China plains due to the higher air temperature and thus higher soil temperature. The negative effect of mulching included a lower emergence and fewer marketable tubers per plant. Nimje (1996) reported that mulching with dry grass @ 5 t ha-1 applied immediately after sowing in between soybean rows controlled weeds effectively (23%) and increased seed yield by 9.3 per cent. Aulakh and Sur (1999) observed the effect of four different mulches (black polythene, white polythene, FYM and Basooti) on soil temperature, weed population, growth and yield in pomegranate. The result showed that the Basooti mulch reduces soil temperature by 1.5oC as compared to 22.4oC recorded under control plots. Polythene mulches 16

significantly reduced the weed population by 19.7 to 26.4 per cent as compared to other mulching material and produced the maximum number of fruit per plant. Ramakrishna et al (2006) conducted on-farm trials in North Vietnam to study the effect of three mulching materials on weed infestation, soil temperature and pod yield of groundnut. Polythene and straw mulch suppressed weed infestation. Polythene mulch increased soil temperature by about 6oC at 5 cm depth and by 4oC at 10 cm depth. Polythene and straw mulch increased pod and stover yield of groundnut significantly over chemical and un-mulched plots. Singh et al (2004) conducted experiment on eight year bearing plum trees on sandy loam soil with three mulch material viz. control, plastic mulch, black polythene mulch and hay mulch. The growth and fruit yield of plum trees increase significantly under mulch treatment. Fruit yield in hay mulch was 93.3 q ha-1 that was 41q ha-1 higher in comparison to un-mulched plots and statistically at par to plastic mulch trees. Rahman et al (2005) reported that rice straw mulch @4 t ha-1 had a significant effect on conserving soil moisture and reducing weed growth, promoting root development and consequently improved grain yield of no till wheat. Kohnke and Werkhoven (1963) found that daily temperature fluctuations at 2.5 cm in bare soil were twice as large as in the wheat-straw mulched (@ 3.75 t ha-1) soil in summer, but mulch less in other seasons. Awan (1964) reported that yield of Sebago potatoes increased from 221 bushels/ acre to 283 and 298 by applying 2 and 4 tonnes, respectively of Hypershenia rufa hay as surface mulch when the plants were 4 week old. The effect of mulch was due to reduction in mid-day soil temperature at 5 cm depth by about 100F. Patil et al (1972) found that application of paddy straw mulch in one month old potato crop increased tuber yield by 20.8 per cent over no mulch on black clay loam soil. Singh et al (1988) used rice straw mulch in field trials with autumn potato and found 15 per cent increase in tuber yield. Application of mulch reduced maximum soil temperature at 10 cm depth by 1-6oC, increased minimum temperature by 0.5-2oC and suppressed weed growth. Sekhon et al (2008) observed 2.4 Mg ha-1 increased in chilli fruit yield with rice straw mulch @ 6 t ha-1 on sandy loam soil. They attributed this yield improvement to lowering soil temperature, more so during early part of the growing season. However, response of crops to mulching depends on soil and climatic conditions. In general, crop responses are more on low water retentive loamy sand compared to sandy loam soils; more intense hot and dry summer period than wet and humid conditions and under limited than plentiful irrigation (Prihar and Arora 1980; Jalota et al 2007). 2.4 Soil moisture conservation with mulch Surface applied mulch is known to conserve soil moisture. According to Army et al (1961) and others, mulch offers increased resistance to water vapour flow from soil surface to the atmosphere by increasing the thickness of the relatively stagnant air above the soil and lowering day time temperature, thus reducing vapour pressure gradient. Rajput and Singh 17

(1970) suggested the use of straw mulch for better moisture conservation and proper development of tubers. Reduction in soil water evaporation with straw mulching decreases crop water demands. In a field study, (Singh et al 1988) reported increase in tuber yield of kufri chandermukhi with rice straw mulch and improved irrigation use efficiency by 14.8 per cent in early sown autumn potato. In a field experiment, Dahiya et al (2007) observed that straw mulching decreased soil water loss on an average by 0.39 mm d-1. Vadi et al (2005) also reported higher soil moisture content at different growth stages of pigeon pea under wheat straw mulch @ 5 t ha-1 in clay soil. Pawar et al (2004) observed that percent increase in soil moisture conservation over un-mulched control was maximum in sugarcane trash mulch (13.6%) followed by black plastic mulch (12.3%), transparent plastic mulch (10.7%) and wheat straw mulch (7.0%). As a result of better moisture conservation, the transparent plastic mulch gave the higher water use efficiency of 37.03 Kg ha-1 cm-1, which was 83.68 per cent more than that of control and proved superior over other mulching methods. Chakravarti et al (2005) also observed that water hyacinth mulch conserved more soil moisture than the other mulches. Acharya and Kapur (2001) reported that application of pine needle mulch on silty clay-loam soil saved one irrigation and gave about 50 and 22 per cent higher potato yield in autumn and spring crop. Pine needle mulching maintained higher soil and plant water status, more roots than no mulching treatment. Chandra et al (2002) also recorded 40 per cent higher water use efficiency with pine needle mulch on sandy loam soil than no mulch plot. Sandhu et al (1992) in a field experiment found that, application of rice straw mulch @ 6 t ha -1 on a loamy sand soil enhanced water expense efficiency by 39 per cent in summer moongbean. An extensive review on benefits of straw mulching reported that this practice saved 7-40 cm of irrigation water in different crops such as maize, sorghum, mentha, sugarcane, potato, moong and winter maize (Jalota et al 2007). Rice straw mulching @ 6 t ha-1 saved 12 cm irrigation water besides improving yield and maintaining 12 mm higher profile moisture (Sekhon et al 2008). Rathore et al (1998) observed the effect of rice straw mulch on conservation of soil moisture under rainfed conditions. They noticed that straw mulch conserved more water in the soil profile during the early growth period compared to no mulch. Conserved soil water regulated proper plant water status and lowered soil mechanical resistance, leading to better root growth and higher grain yield of both chickpea and mustard with straw mulch than no mulch plots. Chaudhary et al (2003) evaluated the effectiveness of different mulching materials like Gliricidia leaves, grass and Lantana as in-situ moisture conservation techniques. All the mulches were found to retain sufficient moisture. However, among the

18

mulch treatments, grass mulch conserved highest moisture followed by Gliricidia and Lantana. Sandhu et al (1980) observed that similar yield of sugarcane was obtained with 34 cm less irrigation water in mulch plots than un-mulched, the beneficial effects being attributed to better soil moisture with mulching. Jalota et al (2001) reported that straw mulch treatment stored more moisture under low evaporativity rainy conditions in three coarse to medium textured soils. Mukherjee et al (2010) studied the effect of different mulching material on water use efficiency and evaporation in tomato crop irrigated with cumulative pan evaporation 50mm, 25mm and rainfed. They observed that actual evaporation rate was 1.82 mm d -1 that declined by 15 and 31 per cent, respectively with mulch. The variation of evapotranspiration among different mulches became more prominent under maximum water stressed conditions. Among different mulches, black polythene mulch was responsible for attaining the highest water use efficiency (25.1 kg m-3), which declined by 22, 21 and 39 per cent under white polythene mulch, rice straw mulch and no mulch, respectively. 2.5 Crop response to nitrogen under mulching Straw mulching also saves fertilizer N for comparable crop yields. Patil et al (1972) observed that application of 60 kg N ha-1 along with rice residue mulch in potato recorded yield comparable to 120 kg N ha-1 without mulch. Saving of 60 kg fertilizer N ha-1 in potato crop with pine needle mulch was recorded by Acharya and Kapur (2001). However, Sood (1986) found that potato tuber yield significantly increased with application of up to 80 kg N ha-1, but the higher dose (120 kg N ha-1) depressed tuber yields. Supplemental irrigation, mulching and N levels did not affect the percentage dry matter in tubers but the application up to 80 kg N ha-1 under supplementary irrigation and mulch resulted in higher uptake of N by potato tubers in normal years, which showed a positive interaction of available soil moisture and nutrient uptake in potato. Straw mulching saved 25 kg N ha-1 in Japanese mint, 50 kg N ha-1 in fodder maize and sorghum respectively (Sandhu et al 1989). Studies on efficient use of urea through water management by Upadhayay et al (1994) reported that crop fertilized with increasing rate of N application (0-180 kg N ha-1) and frequency of irrigation (IW/PAN-E of 1.5, 2.0 and 2.5) registered increase in tuber yield and yield was higher with pre-sowing irrigation. Sekhon et al (2008) observed the application of 45 kg N ha-1 along with rice straw mulch produced same chilli yield as recorded with 75 kg N ha-1 without mulch thus resulting in net saving of 30 kg N ha-1. Field experiments involving application of 2.5-5 t ha-1 straw mulch to organic seed potatoes (S. tuberosum L.) sown in loamy silt soils were conducted by Doring et al (2005) to determine the effects of straw mulch on soil nitrate dynamics. The results indicated that the undesirable post harvest N leaching 19

was significantly reduced due to the immobilization of nitrate-N after harvest at 6.8-7.0 kg N t-1 straw in two experiments (18-34 kg No3 N ha-1). Ruiz et al (1999) observed that use of white polythene and white-black plastic mulch promoted optimal root temperatures for plant growth (23-27oC), showed the highest efficiency of N utilization and the greatest yield of potato tubers (S. tuberosum var. Spunta). Gao et al (2009) conducted field experiment to evaluate the effects of mulching on residual nitrate and N uptake by wheat. The results showed that N uptake and N use efficiency were higher for plastic film mulch and combined mulching with plastic film and straw compared to no mulch. Under these treatments soil nitrate-N contents in the 0-200 cm soil profile were also higher compared to control. Khera et al (1976) studied the independent and combined effect of straw mulch, nitrogen and irrigation on forage corn (Zea maize) and reported that 50 and 100 kg N ha-1 with straw mulch @ 6 t ha-1 yielded as much as 100 kg and 150 kg N ha-1 without mulch, respectively thus indicating a saving of 50 kg N ha -1 with straw mulching. Rahman et al (2005) conducted a field experiment to evaluate optimum application N rate for no-till wheat in the presence of rice straw and observed higher N uptake and apparent nitrogen recovery of applied N fertilizer in mulch treatments. Application of 120 kg N ha-1 with straw mulch was found to be suitable for no till wheat and 160 kg N ha-1 for without mulch. Hundal et al (2000) studied the effect of a combination of three mulches (black, transparent polythene and rice straw) and two mulching techniques (full plot and half meter wide strip) were applied on tomato. Leaf N content, available soil N, NH4 and NO3-N status of the soil after the harvest of tomato crop increased significantly under mulched treatment. Wheat straw as mulch significantly affected the N concentration in maize shoots (Pervaiz et al 2009). 2.6 Effect of straw mulch on soil temperature, soil moisture, nitrogen and yield Nitrogen, irrigation and soil temperature regimes are major factors influencing crop growth. Khera et al (1976) studied the independent and combined effects of straw mulch, nitrogen rates and irrigation on forage corn grown on sandy loam soil which involves two rates of straw mulch i.e. 0 and 6 Mt ha-1, three rates of nitrogen i.e. 50, 100 and 150 kg N ha-1 and three levels of irrigation based on IW/PAN-E ratios of 0.6, 0.9 ad 1.2 and they found that green and dry forage yields and uptake of N significantly increased with mulching and with each successive increment of nitrogen. The green and dry forage yields and nutrient uptake increased significantly with increase in IW/PAN-E ratio from 0.6 to 0.9, but declined with further increase in irrigation. Mulching increased dry forage yield by 11.8 q ha-1 and showed a significant interaction with nitrogen rates viz. 50 and 100 kg N ha-1 with mulch yielded as much as 100 kg and 150 kg N ha-1 without mulch, respectively. Sandhu et al (1989) reported that straw mulching in summer crops reduced evaporative losses from soil, optimized soil temperature, improved crop yield and ensured 20

efficient utilization of the scarce and costly resources of water as well as fertilizer N. In another study, Kumar and Dey (2011) investigated the effect of mulch on root growth, nutrient uptake, water use efficiency and yield of strawberry cv. Chandlu under drip and surface irrigation system on loamy sand. They observed that black polythene mulch conserves 2.80-12.80 per cent more soil moisture. Hay mulch decreased maximum soil temperature (2.7-5.8oC) and increased minimum soil temperature (2.8-5.2oC). Both the mulching material was effective in enhancing root growth, water use efficiency, yield and nutrient uptake. Application of mulch enhanced the root growth (63%), nutrient uptake (179.2%), WUE (84.4%) and yield (343%) under drip irrigation. However, the respective increased under surface irrigation was 23.6, 83.8, 109.4 and 219 per cent. Tan et al (2009) conducted on-farm trial to evaluate the amount and frequency of irrigation as well as the effect of nitrogen fertilizer and straw mulch applications on the performance of bottle gourd and okra. They observed significant interactive effect of frequency and amount of irrigation on the number of nodes and a significant effect of mulching on the number of primary branches. Both number of nodes and primary branches contributed to higher production of bottle gourd. In Okra, low level of nitrogen application (30 kg N ha-1) with low but daily watering had significantly higher yield than higher level of nitrogen application (90 kg N ha-1). Zhang et al (2009) conducted a field experiment in a winter wheat system and observed that mulching decreased daily mean soil temperature at 10 cm depth in the warmer period by 0-4oC and increased in the colder period by 0-2oC when compared to non mulched soil and also conserved 28 and 20 mm more water, respectively in the upper 100 cm soil layer at the time of wheat sowing. Ossom et al (2003) studied the effects organic materials in sweet potato (Ipomoea batatas L.) and reported that grass mulch caused the lowest soil temperatures; coffee husk mulch resulted in the highest K, Mg, Fe, Mn, Cu and Zn concentrations in the tubers; sawdust mulch produced higher dry-matter yield of tubers whereas the grass mulch had the lowest drymatter yield. Kar and Kumar (2007) reported that application of mulch @ 6 t ha-1 helped to conserve more soil moisture and reduce soil temperature by 4-6oC. Higher leaf area index, water use efficiency and intercepted photo-synthetically active radiation were recorded in mulch plots. Gupta and Acharya (1993) studied the effect of mulching material on soil hydrothermal regime, root growth, water use efficiency and yield of strawberry and observed that mulch increased the minimum soil temperature at 5 cm depth, decreased the maximum soil temperature and helped in maintaining high soil moisture. However, total soil-water content up to 60 cm depth, nutrient uptake and WUE was higher with mulch than the unmulched control. Mulch increased strawberry yield by 56 per cent. Study by Sarkar et al (2007) with mulching in yellow sarson (Brassica napus L. var. glauca) reported that morning soil temperature at 0.0-0.2 m depth was 0.1-0.8oC higher under straw mulching and only 0.121

0.4oC at 14:00 hour. Highest (1212 kg ha-1) seed yield was obtained under straw mulching, which was 41 per cent higher when compared with no mulching and WUE was enhanced by 45 per cent. Study by Sarkar and Singh (2006) on a fine loamy soil with barley (Hordigum vulgare L.) observed that straw mulch conserved 19-21 mm of moisture in the 120 cm profile over the un-mulched condition. Both saw dust and rice straw mulching elevated soil thermal status at 07:00 as compared to un-mulched, but this trend was reversed at 14:00. Straw mulching significantly increased grain yield and water use efficiency over un-mulched. In another study Aulakh and Sur (1999) observed that mulch lowered soil temperature by 1.5oC, conserved soil moisture by 4.1 per cent and improved crop growth and yield of pomegranate.

22

CHAPTER III MATERIALS AND METHODS Present investigation was carried out at the research farm of the Department of Soil Science, Punjab Agricultural University, Ludhiana, Punjab, India, during Rabi 2009-10. The details of the materials used and the methods followed are given below: 3.1 Weather and climate Ludhiana is a central district of Punjab, situated at a latitude of 3056 N and longitude of 7552 E at a height of 247 meters above the mean sea level. It is characterized by hot and dry early summers which are followed by a hot and humid monsoon period and cold winters. Mean maximum and minimum temperatures show considerable fluctuations during summer and winter months. Maximum temperature of 45C is common during summer and freezing temperature of 1 to 2C accompanied by frosts is also quite common during December to February. The normal rainfall of the area is 500-750 mm that is mostly received during monsoon period (July to September). The meteorological data for the experimental season were obtained from meteorological observatory of the Punjab Agricultural University located at a distance of about 2 km from the experimental site. The meteorological data of the crop season is given in fig. 3.1a and 3.1b.

40 Maximum Minimum

Air temperature, oC

30

20

10

0 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5

Standard weeks

Fig. 3.1(a) Weekly maximum and minimum temperature during the crop growing season (October 2009 to February 2010)

23

30

Rainfall

PAN-E

RH

100

Rainfall/Evaporation, mm

70 20 40 10 10

0 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5

-20

Standard weeksFig. 3.1(b) Weekly total rainfall, pan evaporation and mean relative humidity during crop growing season (October 2009 to February2010) Mean air temperature ranged from 9.1 to 27.6 C during the cropping season (from 1st October 2009 to 4th February 2010). Weekly minimum temperature of 3.8 C was recorded in the last week of December and maximum temperature of 32.9 C was recorded in the first week of October. Total rainfall received during the cropping season was 49.7 mm with maximum rain of 26.2 mm was recorded in the 1st week of October. Highest evaporation was recorded in the 3rd week of October that is 24.3 mm. The relative humidity during cropping season ranged from 53 per cent in the last week of October to 90 per cent in the 2nd week of January. 3.2 Cropping history of the field Summer moong followed by maize was cultivated in the experimental field during the preceding year prior to the commencement of present studies. 3.3 Experimental details A field experiment was conducted on Loamy sand soil with a plot size of 16.56 square meters. The treatments were replicated thrice and laid out in split-split plot design with mulch in the main plots, irrigation in the sub plots and N levels in sub-sub plots. Layout plan of the field experiment is shown in figure 3.2.

24

Mean relative humidity, %

Non Experimental Area 1 N2 2 N0 3 N1 4 N3 5 N2 Water channel 9 N1 17 N3 10 N3 18 N1 11 N2 19 N0 12 Path N0 20 N2 13 N3 21 N0 Water channel 25 Water channel N2 33 N1 26 N3 34 N2 27 N0 35 N0 28 Path N1 36 N3 29 N3 37 N1 Water channel 41 N2 49 N3 42 N0 50 N0 43 N3 51 N2 44 Path N1 52 N1 45 N2 53 N1 Water channel 57 N0 65 N3 58 N2 66 N1 59 N1 67 N0 60 Path N3 68 N2 61 N2 69 N1 Water channel Main Water Channel Fig 3.2 Layout plan Mulch I1- IW/PAN-E =1.0 N0-Control No mulch I2- IW/PAN-E=1.5 N1-135 kg N ha-1 I3-IW/PAN-E=2.0 N2-180 kg N ha-1 N3-225 kg N ha-1 62 N1 70 N3 63 N3 71 N2 64 N0 72 N0 I2 R3 46 N0 54 N0 47 N1 55 N2 48 N3 56 N3 I3 30 N1 38 N2 31 N0 39 N3 32 N2 40 N0 Non Experimental Area I2 14 N0 22 N2 `15 N1 23 N3 16 N2 24 N1 I3 R1 6 N3 7 N0 8 N1 I2

I1

I1

R2

I1

I3

R1, R2 and R3- Replications

25

3.4 Treatments 3.4.1 Main plot treatments: Mulch levels (Two) No mulch and rice straw mulch @ 6 tones ha-1 Rice straw mulch was spread over the soil surface in selected plots after sowing of potato tuber. 3.4.2 Sub plot treatments: Irrigation levels (Three) Irrigation treatments imposed on the basis of IW/PAN E= 1.0, 1.5 and 2.0 3.4.3 Sub- sub plot treatments: Fertilizer N levels (Four) 0, 135, 180 and 225 kg N ha-1 Well rotten farm yard manure (fresh weight basis) @ 50 tonnes per hectare was uniformly spread in the whole field and incorporated 15 days before sowing of the crop. The moisture content of FYM determined at the time of application was 60 per cent. Number of plots: 2 (Mulch rate) x 3 (Irrigation level) x 4 (Nitrogen level) x 3 (Replications) = 72 3.5 Characteristics of soil The composite soil samples were taken before the sowing of the crop from soil profile with a core sampler at the depths of 0-15, 15-30, 30-60, 60-90, 90-120, 120-150 cm from the field. The soil samples of respective depths were separately analyzed for soil mechanical analysis (Table 3.1), chemical properties (Table 3.2) and physical properties (Table 3.3). The mechanical analysis of the soil samples was done by International pipette method (Piper 1966). The soil of experimental site contained average of 81.8 per cent sand, 9.6 per cent silt and 8.3 per cent of clay. The textural class of the soil samples thus analyzed is loamy sand, as evident from the results presented in table 3.1. The summary of the results obtained from detailed chemical analysis is presented in table 3.2 and the results show that the soil was alkaline in reaction. The pH, EC and organic carbon values varied between 8.28 to 8.59, 0.12 to 0.26 dSm-1 and 0.01 to 0.25 per cent, respectively. Average over profile available N, P and K content in soil were 54.9, 17.4 and 129.8 kg ha-1, respectively. The bulk density of the soil was measured from the soil profile at the depths of 0-15, 15-30, 30-60, 60-90, 90-120, 120150 cm on undisturbed soil by core sample method (Bodman 1942) and maximum water holding capacity of all profile was determined by Keens box method given by Richards (1954) which is presented in table 3.3.

26

Table 3.1 Depth wise mechanical analysis of soil

Depth, cm 0-15 15-30 30-60 60-90 90-120 120-150

Sand 79.5 80.0 82.2 83.5 84.5 81.4

% Silt 11.3 12.6 9.5 8.0 7.5 9.1

Clay 9.2 7.4 8.3 8.5 8.0 8.7

Textural class Loamy Sand Loamy Sand Loamy Sand Loamy Sand Loamy Sand Loamy Sand

Table 3.2 Chemical characteristics of soilSoil Depth, cm Characteristic 0-15 pH (1:2 soil: water suspension) EC dSm-1 (1:2 soil: water suspension) 15-30 30-60 60-90 90-120 120-150 Beckmans glass electrode pH meter (Jackson 1973) Method employed

8.28

8.45

8.48

8.46

8.56

8.59

0.26

0.23

0.19

0.16

0.17

0.12

Solu bridge (Jackson 1967) Walkley and Black rapid titration method (Walkley and Black 1934) Alkaline permanganate method

Organic carbon (%)

0.25

0.12

0.04

0.03

0.01

0.01

Available N (kg ha-1)

75.2

60.2

56.4

47.6

50.1

40.1 (Subbiah and Asija 1956)

Available P (kg ha-1)

32.9

23.9

18.1

11.1

13.0

5.6

0.5 N NaHCO3 extractable P method (pH: 8.5) (Olsen et al 1954) Ammonium acetate extractable K using Flame Photometer (Helmke and Sparks 1996)

Available K (kg ha-1)

162.4

146.4

117.6

112.0

117.4

123.2

27

Table 3.3 Physical properties of soil Depth, cm 0-15 15-30 30-60 60-90 90-120 120-150 Bulk density (Mg m-3) 1.39 1.43 1.49 1.51 1.52 1.57 Water holding capacity (%, v/v) 42.4 43.2 40.1 41.9 41.2 41.4

3.6 Cultural operations 3.6.1 Preparatory tillage A primary tillage operation was done with a tractor drawn disc harrow. A fine seedbed was prepared by two cultivations with a tractor drawn cultivator each followed by planking. Pre-sowing irrigation was applied before bed preparation. Raised seed beds (55 cm wide) alternating with furrows (30 cm wide) were prepared with the help of tractor drawn bed maker. 3.6.2 Variety, seed size, seed treatment and method of sowing Potato variety Kufri chandramukhi was planted on 7th October, 2009 on 55 cm wide beds. Potato tubers weighing 40-50 g each were selected for sowing. Seeds tubers were allowed to sprout for 8-10 days after taking out of cold storage. Seed rate was about 40 q ha-1. To control black scurf, charcoal rot and common scab, tubers were treated with Emisan @ 2.5 g per liter of water for ten minutes. Seed tubers were planted at 5 cm depth in two rows on both sides of bed with 30 cm spacing between tubers. 3.6.3 Irrigation Irrigations were applied according to the following schedule IW/PAN-E ratio 1.0 1.5 2.0 Common irrigation 25/11/09 17/11/09, 1/12/09 12/11/09, 25/11/09, 9/12/09, 2/1/10 31/10/09, 19/12/09 Irrigation dates

28

First common irrigation was applied at 25 days after planting to facilitate germination. Thereafter, the differential irrigation was started as per treatments based on IW/PAN-E ratio. Measured amount of 4.0 cm irrigation water (IW) was applied through Parshall Flume (Parshall 1950). A second common irrigation was applied on 19th December, 2009 for protecting the crop from frost and low temperature. Different soil moisture regimes were created in the soil profile during crop growing season by applying the irrigation on the basis of IW/PAN-E=1.0, 1.5 and 2.0 ratios. These irrigation schedules were maintained in the soil profile during the crop growth period of potato. The treatment on the basis of IW/PANE=2.0 received highest amount of irrigation water 24 cm followed by 16 cm in 1.5 and least amount of water 12 cm in 1.0 ratio besides rainfall. 3.6.4 Fertilizer application The recommended dose of phosphorus (62.5 kg P2O5 ha-1 as single super phosphate), potash (62.5 kg k2O ha-1 as murate of potash) and half dose of nitrogen as per treatment were applied just before the preparation of beds. The remaining half of nitrogen was side dressed as urea before first common irrigation. 3.6.5 Weeding Weeding was done manually on 3rd December and fresh weight of weeds in each plot was recorded. 3.6.6 Plant protection measures. The crop was sprayed thrice at 7 days interval (7/12/09, 15/12/09 and 23/12/09) with a fungicide Indofil M-45 @ 1250 g ha-1 to protect the plant from late blight of potato. 3.6.7 Harvesting The crop was harvested in the third week of January to record fresh weight of both tubers and haulms. Harvesting of tubers was done manually. 3.7 Observations recorded 3.7.1 Soil Temperature Soil temperature was measured with the help of mercury in glass thermometer (soil thermometer) placed at 5 cm depth in mulched and irrigation treatments in triplicate daily at 0730 and 1430 hours. 3.7.2 Soil moisture Moisture content of 0-15, 15-30, 30-60, 60-90, 90-120 cm profile layers was determined at different stages of crop growth by thermo-gravimetric method. Moisture storage in different soil layers was computed as follows: (Mfi Dfi Di) Mi = ---------------------100

29

Where, M = Amount of moisture in the ith layer (cm) Mf = Moisture percentage of the ith layer on dry weight basis Df = Bulk density of the ith layer (Mg m-3) D = Depth of ith layer (cm) The amount of moisture in 0-120 cm soil profile was computed by adding the quantity of moisture in each layer. 3.7.3 Profile water use To estimate the profile water used by the crop, soil water content was measured at the time of sowing and at harvest in 0-120 cm soil profile. The profile water used was calculated by the difference in soil moisture storage at sowing and harvest. Total water use was worked by the sum of the irrigation water applied, profile water used by the crop and rainfall received during the crop growing period. 3.7.4 Water use efficiency (WUE) Water use efficiency of potato crop under different treatments was calculated by the following relationship Potato tuber yield (kg ha-1) WUE (kg ha mm ) = ------------------------------------Water use (mm)-1 -1

3.7.5 Canopy temperature Canopy temperature (Tc) measurements were made using a non-contact infra-red thermometer (AG-42). The instrument was positioned 50 cm above the crop canopy and observations recorded at different dates from 5 randomly selected sites in a plot were averaged to obtain a mean value of Tc. The measurements of canopy temperature were generally made around 1400 hours on relatively clear days. 3.7.6 Chlorophyll content Chlorophyll content of topmost fully expanded leaves was recorded at 87, 92 and 98 days after seeding using a chlorophyll meter (SPAD-502, MINOLTA CAMERA CO-JAPAN) for recording the SPAD (Soil Plant Analysis development) values.. 3.7.7 Yield and yield attributing parameters 3.7.7.1 Tuber and haulm yield of potato Before digging the tubers, above ground plant parts were harvested and weighed to record fresh weight for each plot. A sub sample from each plot was oven-dried to work out the dry weight of haulm in quintal per hectare. Potato tuber weight was recorded from each plot and expressed as quintals per hectare.

30

3.7.7.2 Grading of potato tubers Tubers from each plot were graded by passing through five different sizes of sieves i.e >50, 45-50, 35-45, 25-35, < 25 mm. Weight as well as number of different grades of potato tubers was recorded from each plot. 3.7.8 Plant analysis The tuber and haulm samples were collected from each plot at maturity and dried in hot air oven at 65C. Dried samples were digested with concentrated H2SO4 in the presence of catalyst mixture containing CuSO 4, K2SO4, Se and Hgo. The plant material is oxidized by the H 2SO4 and N is converted to ammonium sulphate. N is determined by distilling the ammonia with 45 per cent Sodium hydroxide solution in the presence of few pieces of granulated zinc which helps in smooth boiling. The ammonia evolved is absorbed in a known excess volume of a standard acid (0.02N H 2SO4), the excess of which is determined by titrating with a standard alkali (0.02N NaOH) using methyl red as indicator. . 3.7.9 Available soil nitrogen Available soil nitrogen was determined by the method described by Subbiah and Asija (1956). Five gram soil was taken in a Kjeldahal distillation flask and moistened with 20 ml of distilled water. After adding 25 ml of 0.32 per cent KMnO4 and 25 ml of 2.5 per cent NaOH solution. The flask was fitted to Kjeldahal assembly. The NH 3 evolved was absorbed in 10 ml of 0.02 N H2SO4 taken in a conical flask. About 30 ml distillate was collected. Three drops of methyl red indicator were added to conical flask. The excess of H2SO4 in the conical flask was titrated against 0.02 N NaOH with change in colour from pink to yellow. 3.7.10 Total N uptake by the plant Total N uptake by the plant is the sum of tuber and haulm N uptake that were calculated as Tuber N uptake, kg ha -1 = Tuber yield kg ha -1 x tuber N content (%) Haulm N uptake, kg ha -1 = Haulm yield kg ha -1 x haulm N content (%)

3.7.11 N use efficiency The fertilizer N use efficiency was calculated for potato crop as under Yield of N treated plot-Yield of controlled plot N use efficiency (kg of tuber kg-1of N applied) = -----------------------------------------------------Applied N

31

3.7.12 Apparent N recovery efficiency The Apparent N recovery efficiency was calculated for potato tuber yield as under and expressed in per cent.

`Apparent N recovery efficiency (kg of tuber kg-1of N applied)

Total N uptake of N treated plot- Total N uptake of controlled plot = Applied N

3.7.13 Statistical Analysis The experimental data was analyzed using analysis of variance technique. The significance of treatment effects was judged with the help of F test (Variance ratio). The critical difference (CD) was used to compare the treatments effects at P 1.5 >1.0 ratio. Data in table 4.5 showed slightly lower under mulched plots TWU while with nitrogen level, TWU increased marginally. The water use increased with the increase in number of irrigations and in case of mulch, water use was lower as compared with no mulch (Chandra et al 2002). Sandhu et al (1992) also reported water expense of the crop increased with increase in irrigation frequency Table 4.5 Total water use as influenced by mulch, irrigation and nitrogen levels during cropping season Total water use, cm Treatment No mulch N0 IW/PAN-E=1.0 N135 N180 N225 Mean N0 IW/PAN-E=1.5 N135 N180 N225 Mean N0 IW/PAN-E=2.0 N135 N180 N225 Mean G. Mean 20.07 20.17 20.57 20.70 20.40 24.07 24.17 24.47 24.67 24.35 29.67 29.77 29.97 30.17 29.90 24.89 Mulch 18.57 18.97 19.07 19.27 18.97 22.27 22.47 22.77 23.07 22.65 28.97 29.17 29.17 29.37 29.53 23.71 Mean 19.32 19.57 19.82 20.02 19.68 23.17 23.32 23.62 23.87 23.50 29.32 29.47 29.57 29.77 29.53

4.7 N content N content in tuber and haulm of potato was determined at harvest of the crop under mulch, irrigation and N treated plots (Appendix I and II). The N content of tuber and haulm were significantly influenced by the mulching and nitrogen treatments as given in figure 4.9 (a and b) whereas, affect of irrigation scheduling was noticed in haulm only. In general haulm had more content of N than the tubers of potato. Haase et al (2007) also noticed same trend and reported that N concentrations were significantly influenced by fertilization. The value of N content in haulm and tuber were 2.79 and 1.35 per cent with application of rice straw mulch 53

while, it was 2.63 and 1.14 per cent with no mulch plots, respectively. The N content varied from 2.51, 2.67, 2.77 and 2.89 per cent, respectively with application of 0, 135, 180 and 225 Kg N ha-1 in haulm. The corresponding values for tuber were 0.92, 1.26, 1.38 and 1.41 per cent, respectively. Irrigation schedule on the basis of IW/PAN-E=1.0, 1.5 and 2.0 recorded N content by 2.55, 2.75 and 2.78 per cent, respectively in case of haulm. Jamati-e-Somarian et al (2010) also recorded the highest nitrogen percent of tuber by applying 80 kg N ha-1 and decrease as the level of fertilizer increases.

2.00 No mulch Mulch

N content, %

1.00

0.00 0 135 Nitrogen level 180 225

Fig 4.9(a) N content (%) in potato tuber as influenced by mulch and N levels at harvest

3.00

No mulch

Mulch

N content, %

2.00

1.00

0.00 0 135 Nitrogen level 180 225

Fig 4.9(b) N content (%) in potato haulm as influenced by mulch and N levels at harvest 54

4.8 Yield and yield attributes 4.8.1 Tuber yield Mulching with rice straw significantly influenced the tuber and haulm yield of potato (Table 4.6 a and b). Application of mulch @ 6 t ha-1 enhanced potato tuber yield by 49.3 q ha-1 (25%) over no mulch plots. Singh et al (1987) also reported 26 per cent increase in yield of potato owing to mulch. Similarly, Chandra et al (2002) also observed that pine needle mulch increased the tuber yield by 35 per cent over no mulch. Tuber yield of potato was also significantly affected by irrigation and N levels. irrigation based on IW/PAN-E ratio of 2.0 and 1.5 significantly enhanced average tuber yield of potato by 25.8 and 19.1 q ha-1 over the restricted irrigation with 1.0 ratio (206.7 q ha-1). Singh et al (1988) also observed that irrigation with 0.25 bar tension increased tuber yield by 22 per cent compared with irrigation applied at 0.5 bar tension. Similarly Kar and Kumar (2007) also recorded a drastic reduction of potato tuber yield when the number of irrigation was reduced. Sandhu et al (1980) observed an increase in cane yield by an average of 13.8 per cent for 1.00 over the 0.50 times pan evaporation. Tuber yield of potato at harvest under various level of nitrogen is given in table 4.6 (a). Nitrogen applied @ of 135, 180 and 225 kg ha-1 improved the tuber yield by 58.4, 73.3 and 86.5 per cent, respectively over 143.4 q ha-1 obtained in control. It is explicitly clear from the table that the tuber yield improved with increasing rate of application of N and attained highest value with 225 kg N ha-1 at all the levels of irrigation over their respective control. Significant interaction between mulching and nitrogen levels revealed that tuber yield of potato increased with increase in nitrogen levels up to 225 kg ha-1 in no mulch plots (Table 4.6 b). However in mulched plots significant improvement in tuber yield was recorded up to 180 kg N ha-1 only. Lower level of nitrogen (135 kg ha-1) with straw mulching produced the higher yield than the yield obtained with 225 kg N ha-1 without mulch. This indicates that mulching can save nitrogen fertilizer in autumn potato grown in loamy sand soil. Khera et al ( 1976) found a significant interaction of mulch N and observed 26 per cent increase in the dry forage yield and also revealed that 50 and 100 kg N ha-1 with mulch yielded as much as 100 and 150 kg N ha-1 without mulch, respectively. The interactive effect of irrigation schedule and mulching revealed that potato tuber yield improved with increase in irrigation frequency up to IW/PAN-E=2.0 while in mulched plots, enhancement was observed upto 1.5 ratio only. This shows that with use of mulch the optimum irrigation schedule is 1.5 for obtaining maximum yield. Perusual of data in table 4.6 (a) depict that restricted irrigation with 1.0 ratio in mulched plots register higher yield compared to yield obtained in frequently irrigated plots (IW/PAN-E=2.0) with no mulch treatment. This indicates that use of rice straw mulch can save substantial amount of irrigation water in autumn potato. Interaction between irrigation and fertilizer-N in (Table 4.6 a) was significant indicating that improvement in tuber yield recorded with increasing nitrogen 55

varied at different irrigation levels. Improvement in tuber yield with application of 135,180 and 225 kg N ha-1 was lower (82.4, 91.0 and 110.1 q ha-1) in 1.0 ratio compared to 83.9, 110.3 and 133.5 q ha-1 in 1.5 and 85.2, 114.5 and 128.9 q ha-1, respectively in 2.0 ratio over their respective control value of 135.9, 143.9 and 150.4 q ha-1. Interaction between mulch, irrigation and nitrogen levels revealed that with no mulch, tuber yield enhanced with nitrogen levels from 0 to 225 kg N ha-1 and at all the levels of irrigation. However, with mulching, the improvement up to 225 kg N ha -1 was observed only in optimum irrigation schedule on the basis of 1.5 ratio whereas, under restricted or frequently irrigation, tuber yield increased up to 180 kg N ha-1 only. This indicates that for obtaining potential yield, both irrigation and nitrogen should be supplied at optimum proportion. Straw mulching improved the growth, development and yield of potato through moderation of soil temperate (Dhesi et al 1964), conservation of soil water and reduction in weeds growth. The improvement in growth and yield with mulch may be attributed to the lowering of daytime soil temperature and increase in moisture supply to the crop. This is supported by the studies of Singh et al (2010), Maurya and Lal (1981) and Midmore et al (1986) who indicated soil moisture conservation and reduction in soil temperature by mulching may cause yield improvement in various crops. 4.8.2 Haulm yield A similar trend was observed with respect to dry weight of potato haulm as was observed in case of tuber yield of potato. Dry weight of haulm was significantly influenced by mulch, irrigation and N levels (Table 4.7 a and b). Application of mulch enhanced weight of haulm yield by 2.29 q ha-1 (26.8%) over the no mulch plots. Whereas irrigation on the basis of 2.0 and 1.5 ratio increased the haulm yield by 18.7 and 6.2 per cent over the value of 8.92 q ha-1 in 1.0 ratio. The application of N @ 135, 180 and 225 kg ha-1 also improved significantly the haulm weight by 5.1, 6.9 and 8.7 q ha-1, respectively over the control plots. Dry weight of haulm indicated significant interaction between mulch and nitrogen level (Table 4.7 b). Application of 135, 180 and 225 kg N ha-1 increased dry matter yield by 5.5, 8.7 and 9.8 q ha-1 in mulch plot and 4.6, 5.1 and 7.6 q ha-1 in no mulch plots, respectively over their respective control values of 4.8 and 4.2 q ha-1. Improvement in dry matter production with application of nitrogen was more in mulch plots as compared to no mulch. Khera et al (1976) also observed that straw mulch @ 6 t ha-1 increases the dry forage yield by 11.8 q ha-1 and shows a significant interaction with N rates. They also observed that irrigation based upon IW/PAN-E ratio from 0.6 to 0.9 green and dry forage yield of maize increased significantly. Similar observation on chilli biomass was recorded by Sekhon et al (2008) that increase in biomass ranged from 29 to 35 per cent during different cropping seasons due to mulch. They also observed chilli biomass was also significantly affected by N level. Wien et al (1993) reported that the increased above ground growth of tomato with mulching. 56

Table 4.6 (a) Tuber yield influenced by mulch, irrigation and nitrogen levels Tuber yield, q ha-1 Treatment No mulch N0 IW/PAN-E=1.0 N135 N180 N225 Mean N0 IW/PAN-E=1.5 N135 N180 N225 Mean N0 IW/PAN-E=2.0 N135 N180 N225 Mean G. Mean CD (0.05) 124.2 186.6 200.3 238.3 187.4 123.2 199.2 215.7 244.6 195.7 135.0 211.2 229.1 256.9 208.0 197.0 Mulch 147.5 249.9 253.4 253.6 226.1 164.6 256.3 292.6 310.1 255.9 165.7 260.0 300.7 301.6 257.0 246.3 Mean 135.9 218.3 226.9 246.0 206.7 143.9 227.8 254.2 277.4 225.8 150.4 235.6 264.9 279.3 232.5

M= 8.05, I= 4.03, N= 5.62, M x I= 5.70, M x N= 7.95, I x N= 9.74 and M x I x N= 13.77

Table 4.6 (b) Interaction between mulch and nitrogen in tuber yield Tuber yield, q ha-1 Nitrogen level No mulch N0 N135 N180 N225 Mean CD (0.05) 127.5 199.0 215.0 246.6 197.0 Mulch 159.3 255.4 282.2 288.4 246.3 M x N= 7.95 Mean 143.4 227.2 248.6 267.5

57

Table 4.7(a)

Dry weight of potato haulm as influenced by mulch, irrigation and nitrogen levels at harvest Dry haulm yield, q ha-1 Treatment No mulch N0 3.5 8.4 8.9 10.8 7.9 N0 4.0 8.7 9.2 11.4 8.3 N0 5.2 9.4 9.7 13.3 9.4 8.52 Mulch 4.1 9.3 12.5 14.0 10.0 4.5 10.4 13.3 14.4 10.7 5.9 11.3 14.7 15.3 11.8 10.81 Mean 3.8 8.9 10.7 12.4 8.92 4.3 9.6 11.3 12.9 9.48 5.6 10.4 12.2 14.3 10.59

IW/PAN-E=1.0

N135 N180 N225

Mean

IW/PAN-E=1.5

N135 N180 N225

Mean

IW/PAN-E=2.0

N135 N180 N225

Mean G. Mean CD (0.05)

M= 0.92, I= 1.00, N= 0.73, M x I= NS, M x N= 1.03, I x N=NS and M x I x N= NS

Table 4.7(b) Interaction between mulch and nitrogen in potato haulm yield at harvest Dry haulm yield , q ha-1 Nitrogen level No mulch N0 N135 N180 N225 Mean CD (0.05) 4.2 8.8 9.3 11.8 8.5 Mulch 4.8 10.3 13.5 14.6 10.8 M x N= 1.03 Mean 4.5 9.6 11.4 13.2

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4.9 Water use efficiency (WUE) The water use efficiency is an index to quantify the use efficiency of water resources towards crop production. The WUE of the crop under various treatments of mulch, irrigation and Nitrogen levels is presented in table 4.8 (a and b). Though mulch application had marginal effect on profile water use, its application with various irrigation and nitrogen levels improved the tuber yield substantially and thus, recorded significantly higher WUE of potato. It reflects that stored water was more efficiently used by crop with application of mulch to these treatments. It is evident from the data that rice straw mulch significantly increased WUE by 26.2 kg tuber ha-1 mm-1 over no mulch plots. Sarkar et al (2007) also observed 0.8-1.2 kg ha-1 mm-1 higher WUE by straw mulching over the un-mulch conditions. Application of 135, 180 and 225 kg N ha-1 also registered higher WUE (57.3, 69.7 and 80.9%, respectively) over without N plot. Contrary to TWU, WUE was progressively decreased with each increment in irrigation water inputs. The data explicitly shows that the improvement of WUE with IW/PAN-E= 1.5 and 1.0 was 17.6 and 26.4 kg tuber ha-1 mm-1, respectively higher than the frequently irrigated 2.0 (78.8 kg ha-1 mm-1) plot. The interactive effect of irrigation and mulching revealed that improvement in WUE of crop with mulch was 28 and 35 per cent more in 1.5 and 1.0 ratio over the 2.0 ratio, whereas the corresponding value in no mulch plots was 15.2 and 31.6 per cent, respectively. Higher WUE due to mulching over no mulch plot have been reported by many workers (Chandra et al 2002, Singh et al 1987 and Singh et al 1988) that was attributed to the reduction in evaporation loss through organic mulch (Aggarwal et al 1992 and Aggarwal and Sharma 2002). Significant interaction between mulch nitrogen levels revealed that improvement in WUE was up to 180 kg N ha-1 in mulch plots while under no mulch improvement recorded up to 225 kg N ha-1. Per usual of data indicate that application of rice straw mulch can save 45 kg N ha-1 for obtaining similar WUE (Table 4.8 b). Interaction between irrigation fertilizer N was also found significant and increase in WUE under restricted and medium irrigation level was observed up to 225 kg N ha-1 whereas, with frequently irrigated plots it was noticed only up to 180 kg N ha-1. Interaction between mulch irrigation nitrogen revealed that mulching along with optimum irrigation level of IW/PAN-E=1.5, improvement in WUE was recorded up to 225 kg N ha-1 where as in restricted and frequent level of irrigation was noticed only up to 180 kg N ha -1. In no mulch plots WUE increased with each successive increment in nitrogen level at all levels of irrigation (Table 4.8 a).

59

Table 4.8(a) Water use efficiency of potato as influenced by mulch, irrigation and nitrogen levels WUE, kg ha-1 mm-1 Treatment No mulch N0 IW/PAN-E=1.0 N135 N180 N225 Mean N0 IW/PAN-E=1.5 N135 N180 N225 Mean N0 IW/PAN-E=2.0 N135 N180 N225 Mean G. Mean CD (0.05) 61.9 92.5 97.4 114.7 91.6 51.0 82.4 88.1 99.1 80.2 46.0 70.9 76.4 85.1 69.6 80.4 Mulch 79.0 131.7 132.9 131.6 118.8 74.0 114.0 128.4 134.4 112.7 57.0 89.1 103.0 102.6 88.0 106.5 Mean 70.4 112.1 115.1 123.2 105.2 62.5 98.2 108.3 116.8 96.4 51.5 80.0 89.8 93.9 78.8

M= 3.7 I=2.0, N=2.3, M x I=2.1, M x N=3.3, I x N=4.1 and M x I x N=5.7

Table 4.8(b) Interaction between mulch and nitrogen in water use efficiency of potato WUE, kg ha-1 mm-1 Nitrogen level No mulch N0 N135 N180 N225 Mean CD (0.05) 52.9 81.9 87.3 99.7 80.45 Mulch 70.2 111.6 121.5 122.9 106.55 M x N=3.3 Mean 61.5 96.8 104.4 111.3

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4.10 Total N uptake The N uptake by potato haulm and tuber were estimated separately by multiplying the N content in haulm and tuber with their respective yield obtained on dry weight basis. Total N uptake was obtained by sum of the N uptake by tuber and haulm of potato is given in table 4.9(a). Total N uptake in potato was found to be significant with the application of mulch and it was increased by 41.4 per cent over the N uptake of 76.4 kg ha-1 in no mulch plots. Sekhon et al (2008) also observed an increase in total N uptake by 18.7 per cent with mulching. Average N uptake increased significantly by 13 and 24.9 per cent with irrigation on the basis of IW/PAN-E= 1.5 and 2.0 ratio over the 1.0 ratio (81.8 kg ha-1). Application of N at various rates also influenced significantly the N uptake of potato and it was found to be enhanced by 47.6, 68.1 and 84.9 kg ha-1, respectively with 135, 180 and 225 kg N ha-1 over the uptake of 42.1 kg ha-1 in without N plots. Acharya and Sharma (1994), Rahman et al (2005) and Pervaiz et al (2009) also reported an increase in N uptake in mulched plots and also increase with increment in N levels. Similarly Kumar and Dey (2011) observed positive and significant effect of mulch as well as irrigation methods on the N uptake. Total N uptake in potato shows significant interaction between mulch and nitrogen (Table 4.9 b). Data reveals that uptake of N in mulch crop was more by 82.4, 84.1 and 93.8 kg ha-1 with application of 135, 180 and 225 kg N ha-1, respectively over the N uptake of 50.5 kg ha-1 in control plots, while in no mulch plots corresponding increase was 42.8, 52.2 and 66.8 kg ha-1, respectively over the 33.7 kg ha-1 in control plots. Khera et al (1976) also observed significant increase in N uptake with mulching and with each successive increment of nitrogen in forage corn. They also observed significant increase in nutrient uptake as the irrigation level increase from 0.6 to 0.9 IW/PAN-E ratio, but declines with further increase in irrigation. 4.11 Fertilizer-N use efficiency Similar to water use efficiency agronomic fertilizer-N use efficiency (NUE) was also improved by mulching. The data in table 4.10 shows that with application of mulch, 26 per cent improvement in NUE was recorded compared to 51.5 kg tuber kg-1 N with no mulch plots. The highest NUE 61.1 kg tuber kg-1

N was recorded under 135 kg N ha-1 followed by

58.5 kg tuber kg-1 N in 180 kg N ha-1 and 55.2 kg tuber kg-1 N in 225 kg N ha-1. In general NUE was decreased with increase in N rate at all levels of irrigation schedules irrespective of mulch. Irrigation schedules also influence the fertilizer N use efficiency. The lowest value was recorded in least frequently irrigated plots (IW/PAN-E=1.0) 52.2 kg tuber kg-1 N where as in other two irrigation schedules on the basis of 1.5 and 2.0 ratio , the value of N use efficiency was similar (61.1 and 61.4 kg tuber kg-1 N).

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Table 4.9(a) Total N uptake as influenced by mulch, irrigation and nitrogen levels at harvest N uptake, kg ha-1 Treatment No mulch N0 IW/PAN-E=1.0 N135 N180 N225 Mean N0 IW/PAN-E=1.5 N135 N180 N225 Mean N0 IW/PAN-E=2.0 N135 N180 N225 Mean G. Mean CD (0.05) 27.3 66.4 77.4 101.9 68.2 35.1 77.9 85.4 109.6 77.0 39.3 83.9 95.4 117.3 84.0 76.4 Mulch 40.8 91.4 120.5 129.5 95.6 51.8 104.7 131.6 144.6 108.2 58.9 112.8 151.3 159.2 120.5 108.08 Mean 34.1 78.9 99.0 115.7 81.8 43.5 91.3 108.5 127.1 92.5 49.1 98.4 123.4 138.3 102.2

M= 6.03, I= 3.71, N=2.96, M x I= NS, M x N= 4.18, I x N= NS and M x I x N= NS

Table 4.9(b) Interaction between mulch and nitrogen in total N uptake at harvest N uptake, kg ha-1 Nitrogen level No mulch N0 N135 N180 N225 Mean CD (0.05) 33.7 76.5 85.9 109.6 70.4 Mulch 50.5 102.9 134.6 144.3 108.0 M x N= 4.18 Mean 42.1 89.7 110.2 127.0

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Table 4.10 Fertilizer-N use efficiency (NUE) as influenced by mulch, irrigation and nitrogen levels NUE, kg tuber kg-1 N Treatment No mulch N135 IW/PAN-E=1.0 N180 N225 Mean N135 IW/PAN-E=1.5 N180 N225 Mean N135 IW/PAN-E=2.0 N180 N225 Mean G. Mean 46.2 42.3 50.7 46.4 56.3 51.4 54.0 53.9 56.4 52.3 54.2 54.3 51.5 Mulch 78.3 58.8 47.1 61.4 68.0 71.1 64.7 67.9 69.9 75.0 60.4 68.4 65.9 Mean 62.3 50.6 48.9 53.9 62.2 61.3 59.4 60.9 63.2 63.7 57.3 61.4

Table 4.11 Apparent N-recovery efficiency as influenced by mulch, irrigation and nitrogen level N recovery, % Treatment No mulch N135 N180 N225 Mean N135 IW/PAN-E=1.5 N180 N225 Mean N135 IW/PAN-E=2.0 N180 N225 Mean G. Mean 29.7 28.0 33.0 30.2 31.8 27.9 33.2 30.9 33.7 31.1 35.1 33.3 31.5 63 Mulch 37.6 44.4 39.7 40.6 39.6 44.5 41.0 41.7 39.3 51.3 44.3 45.0 42.4 Mean 33.7 36.2 36.4 35.4 35.7 36.2 37.1 36.3 36.5 41.2 39.7 39.2

IW/PAN-E=1.0

4.12 Apparent nitrogen-recovery efficiency Apparent N recovery (ANR) efficiency was estimated by N uptake of N treated plots minus N uptake without N plots divided by N added expressed in percentage. The N recovery efficiency at various levels of N, irrigation and mulching is given in table 4.11. It indicates that with application of rice straw mulch higher N recovery efficiency (34.6%) was recorded over the value of 31.5 per cent in no mulch plots. It showed that mulching helped to improve fertilizer N recovery efficiency substantially. Irrigation regime on the basis of IW/PAN-E=2.0 recorded the higher N recovery efficiency 39.2 per cent followed by 36.3 per cent in 1.5 ratio and lowest 35.4 per cent under 1.0 ratio. Mean of N recovery efficiency over irrigation and mulch recorded that N recovery efficiency was increased up to 180 kg N ha-1 only. Rahman et al (2005) also observed decrease in ANR per cent with increase in N level from 80 to 160 kg N ha -1. Sieling et al (1988) and Raun et al (1999) also reported similar trend of apparent nitrogen-recovery. 4.13 Available soil nitrogen at harvest Available soil N was determined at harvest in each treatment and found to be significantly affected by mulch, irrigation and N levels (Table 4.12 a and b). Surface applied mulch having 64 kg ha -1 lower N at the time of potato harvest against the 104.4 kg N ha-1 in un mulch plots. It shows that mulched crop consume more N as a consequence lower value of available N under this treatment. Available N content of soil at time of harvest also influence by the irrigation levels imposed on the basis of IW/PANE ratio. The highest available soil N was observed in 1.0 ratio (104.4 kg ha -1) followed by 1.5 (101.1 kg ha -1) and lowest in 2.0 ratio (97.9 kg ha -1). It indicates that as the irrigation frequency increased, it improves N uptake by crop as a results decrease in the soil N status of the soil. An increase in the N rate application to the soil there was increased in the available N at harvest. The improvement in left over N was 14.3, 43.6 and 60.6 kg ha -1, respectively with application of 135, 180 and 225 kg N ha -1 over 71.5 kg ha-1 without N treatment. The interactive effect of mulch and nitrogen was also found to be significant shown in table 4.12 (b). Interaction shows that the improvement in available N with 135, 180 and 225 kg N ha-1 was 23, 63 and 90 per cent, respectively in no mulch plots over the control (72.4 kg ha -1). The corresponding increase was 17, 58 and 79 per cent, respectively in mulch plots.

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Table 4.12 (a) Effect of mulch, irrigation and fertilizer N application on soil available nitrogen at harvest Available soil N, kg ha-1 Treatment No mulch N0 N135 N180 N225 74.4 94.6 121.9 141.2 108.0 N0 N135 N180 N225 Mean N0 N135 N180 N225 Mean G. Mean CD (0.05) 73.3 87.7 119.7 138.6 104.8 69.5 84.8 112.6 132.9 99.9 104.4 Mulch 72.1 83.6 116.4 130.7 100.7 70.3 82.7 111.3 125.3 97.4 69.6 81.1 108.6 123.7 95.7 98.0 Mean 73.2 89.1 119.1 135.9 104.4 71.8 85.2 115.5 132.0 101.1 69.6 83.0 110.6 128.3 97.9

IW/PAN-E=1.0

Mean

IW/PAN-E=1.5

IW/PAN-E=2.0

M= 4.04, I= 2.61, N= 2.73, M x I= NS, M x N= 3.86, I x N= NS and M x I x N= NS

Fig 4.12(b) Interaction between mulch and nitrogen on soil available nitrogen at harvest Available soil N, kg ha-1 Nitrogen level No mulch N0 N135 N180 N225 Mean CD (0.05) 72.4 89.0 118.1 137.6 104.2 M x N= 3.86 Mulch 70.6 82.5 112.1 126.6 97.9 Mean 71.5 85.8 115.1 132.1

65

>50 100% 80% 60% 40% 20% 0%

45-50

35-45

25-35

50 100% % contribution 80% 60% 40% 20% 0% 1.0

45-50

35-45

25-35

50 100% 80% 60% 40% 20% 0% 0

45-50

35-45

25-35

50 100% 80% % contribution 60% 40% 20% 0%

45-50

35-45

25-35

50 100% 80% % contribution 60% 40% 20% 0% 1.0

45-50

35-45

25-35

50 100% 80% 60% 40% 20% 0% 0

45-50

35-45

25-35

300 g) tubers by weight than the non-mulched treatment. Per cent contribution of larger size (>50 mm diameter) tubers towards yield was 39.6 as compared to 26.6 under no mulched plots. However the contribution of medium sizes (25 to 45 mm diameter) of tubers was more in no mulch plots. The diameter of 50-45 mm and 50 mm weight of potato tuber was lowest while 35-50 mm diameter of tubers contribution was higher with crop irrigated on the basis of IW/PAN-E=1.0. Irrigation schedule on the basis of 1.5 and 2.0 ratio produce similar per cent tuber (Appendix III). The contribution of different grades of potato tubers was also influence by N application. The contribution of >50 mm diameter tuber weight increased with increase in rate of fertilizer N up to 225 kg ha-1. The contribution of this size tuber towards total yield at harvest was 15.6, 33.0, 39.7 and 43.9 per cent, respectively with 0,135, 180 and 225 kg N ha -1. The tuber diameter of 135 >180 >225 kg N ha-1. The contribution of 35-45mm diameter was identical in different N treatments except in 135 kg N ha -1 where it was slightly higher. The interaction between mulch, irrigation and nitrogen were also found to be significant for contribution in yield from more than 35 mm diameter of potato tuber. Yuan et al (2003) also reported highly significant increase in total marketable (>85 g) and jumbo (>400 g) tuber yields as the irrigation level increase from 0.25 to 1.25 EP, which is similar to the results obtained by Hang and Miller (1986) and Meyer and Marcum (1988). Increase in the yield of large tuber size increased with increase in N levels confirming the results of Singh (1952), Gupta