Dry and Wet Spells and Ridging Tied-ridging of Vertisol ...

Nile Water Science & Engineering, Vol. , Issue
Dry and Wet Spells and Ridging Tied-ridging of Vertisol Effect on SorghumYield and Soil Moisture Variability, North Gondar, Ethiopia
Ertiban Wondifraw , Muuz Gebretsadik , Sisay AMBACHEW Melkie Desalegn
Gondar Agricultural Research Centre,Amhara Agricultural Research Institute, Ethiopia College of Agriculture and Environmental Science, Adigrat University, Ethiopia College of Agriculture and Rural Transformation, University of Gondar, Ethiopia
Abstract Vertisols are soils that have high clay content and properties with swelling and cracking nature depending on the extreme water contents. These extreme water contents make vertisols inappropriate for traditional farming. Sorghum is a major and one of the leading traditional food crops in Ethiopia with approximately 297,000 ha production area coverage per annum, which comprises 15-20% of the total cereal production in the country. It is the fourth most important world cereal after wheat, rice and maize.This study was conducted in Gondar zuria wereda, North Gondar zone, Ethiopia; with the aim of investigating dry spell and wet spell periods and their effect on soil moisture variability and on sorghum yield and yield components.To limit effect of extreme soil water conditions for sorghum production, timing of ridging tie-ridging on the yield and yield components of sorghum was studied. The timing ofridging and tied ridging experiment was implemented during 2014 to 2016 seasons at
nant. Ridges were developed manually. Triplicate eight treatments, with seven ridging tied ridging timings and one control, were compared for the grain and stover yield of sorghum. Fertilizer inputs (87kg N and 46 kg P O per hectare) were supplied equally for each plot.Daily rainfall data with 46years was used to analyze wet/dry spells and climatic data of 10 years was used to calculate daily evapotranspiration using Penmanmonthieth equation. Dry spell and wet spell analysis was done using first order Markov chain modeling. Single soil moisture sampling of eachtreatmentwas monitored using gravimetric method in weekly basis at soil depth intervals of 0- 20cm and 20-40cm.Means of yieldtreatment effects were compared at 5% significance level.An appropriate time of ridging and tied ridging was identified based on probability occurrence of wet period which contribute excess moisture and the dry spell period which requires moisture conservation ahead of the first dry spell day. Aligning with the growth period of sorghum, both dry spell and wet
experiments of ridging and tied-ridging supported the stochastically forecasted wet period and dry period in both soil moisture status and sorghum yield effect. Therefore, flat at planting that support the seed establishment; ridging 3 weeks after planting that removes the excess water; tying 9 weeks after planting which conserves some moisture ahead of the first dry spell day set, was selected as an appropriate time of vertisol water management in the study area. Despite financialfeasibility, farmers of the locality can apply this solution to secure the failure of sorghum yield due to excess rain and probabilistic dry spell occurrence at some stages of the crops.
Keywords: Dry and wet spell, tie-ridging, time, sorghum, vertisol
INTRODUCTION
It is proven that current food demand of Sub-Saharan countries is increasing mainly driven by population increase(Sasson, 1990).Yet, the climate variability is a main factor that influences the annual crop productivity in this region (Thornton et al. 2006; E. Boelee et al.2013), despite many efforts which have been carried out to reduce consequences of these effects and resulted with significant outputs such as increasing crop productivity through intensive agricultural management practices. In Ethiopia, extreme weather events have resulted in food shortages and famines in the past (Gray and Mueller 2012; Cheung et al., 2008; Conway and Schipper 2011; Mersha and Boken 2005)
-holder farmers whose economy depends on agriculture have to improve the management of current climate variability (Muller et al., 2011; Tseganeh et al., 2013).
One of the biophysical and socioeconomic factors, soil water management has crucial contribution on the expected agricultural production. Vertisols are soils that have high clay content and properties with
swelling and cracking nature depending on the extreme water contents. These extreme water contents make vertisols inappropriate for traditional farming (Swindale, 1988). The extent of vertisols in Africa may reach or even exceed 120 million hectares. In Ethiopia, mainly in the rift valley and Ethiopian plateau, the extent of vertisol is about 13million hectares (Ahmed N.,1996). The spatial distribution of these soils is more scattered that mainly dominates in the western part of the country. Origin of the vertisols in Ethiopian highlands can be a Basaltic rocks of volcanic. (Kantor and Schwertmann, 1974; Murthy et al., 1982).
Improved vertisols managements had been practicing in the world where this type of soil exists (Wani et al., 2013). Crop production in vertisols requires special water management practices in areas with high and limited rainfall (Ahmed N., 1996). Retaining the limited rain in vertisols of arid and semi-arid regions through tillage or surface roughening compounded with graded furrows, contouring or furrow diking i.e, tied ridges (Nyakudya and Stroosnijder, 2014), increasing the infiltration rate of the limited rainfall (Wiyo et al., 2000; Rockst rm J., 2002) or creating opportunity time, hence, draining excess water on vertisols of humid regions are concurrent solutions of increasing crop productivity. Ridges with tied furrows are most common in Zimbabwe with the objective to save the rainfall where it falls mainly for maize, sorghum and cotton production (Jones et al., 1989).
To increase the yield of barley, sorghum, teff grown in vertisols of Ethiopia, many efforts have been doing in areas with high and low rainfall distribution. Tied ridging isa cropped small bund that conserves direct rainfall (Ngigi S.N., (2003). Despite its laborious and time consuming nature (Araya and Stroosnijder, 2010), tied ridging is a proven practices to conserve soil moisture in semi-arid areas (Biazin B., et al., 2012).Ridging can be designed as open or closed (tied) for holding water and facilitating infiltration in areas of low, erratic rainfall. In tied ridging, sometimes called tied-furrows, ridge furrows are blocked with earth ties spaced on fixed intervals to form a series of micro-basins in the field (Nyamudeza and Jones, 1994; Wiyo et al., 1999; Biazin B., et al., 2012).
Sorghum (Sorghum bicolor L. Moench) is a crop domesticated in Africa (Kumar et al., 2011), which grows predominantly in Ethiopia (CSA, 2014). It is a major and one of the leading traditional food crops in Ethiopia with approximately 297,000 ha production area coverage per annum (Wortmann et al., 2006) which upgraded to more than 1.6million hectare in 2014/5 production season and comprises 15- 20% of the total cereal production in the country (Berhanu, 2016). Despite wide adaptation range of its varieties (Gebretsadik R., et al., 2014), yield of sorghum, as other crops is affected with high variability of rainfall and other climatic variables. Neither hybrid practice is there (MindayeT., 2016) nor new varieties could easily adopted with farmers and gave better yield in the highlands of Ethiopia.
Ethiopia, research works related to vertisol moisture management in semi-arid agro-ecology show their positive impact on soil moisture increment. Tied-ridging increase soil water in the root zone by 24% (McHugh et al., 2007) and by at least 13% which brought 44% yield increase of barley (Araya and Stroosnijder, 2010) as compared to traditional tillage in rain season.
Besides to the adoption of ridging practice for soil moisture under cropping, it is necessary toexplore the time of ridging for better crop growth.According to Birhane et al. (2006); tied ridging before or at planting in arid areas of Tigray region, Ethiopia;resulted with optimum soil water status togetherand improved the performance of a crop compared with tied ridging after planting. However, Temesgen(2007)studied that in the semi-arid Rift Valley of Ethiopia, the interval between tied-ridging and sowing has affected water conservation efficiency and the maize yield negatively under minimum rainfall of the time.
However, in heavy rainfall seasons, tied-ridging could cause water logging on maize and sorghum. Strategies to address this are needed. (Biazin B., et al., 2012).
The objective of this research is:
To identify the probability of dry spells and wet spells of the study area.
To assess the effect of riding and tied ridging in soil moisture variability
To evaluate the ridging and tied ridging timeoncompromising the rainfall extremes for growth and yield of Sorghum
MATERIALS AND METHODS
Description of Study Area The experimental agricultural field is found 40km East of Gonder town. It is found in Gumara- maksegnit watershed laid under Lake Tana basin, the main tributary of Blue Nile. The watershed is
The annual mean maximum temperature of this watershed is 32ºc while its annual mean minimum temperature is 13ºc. Overall, it receives mean annual rainfall near to 1052mm with high standard deviation. The dominant land use is cultivated land with crops varying from cereals to legumes.
The livelihood of the area mainly depends on agriculture that includes livestock and crop production. Farmers use small scale agricultural system using oxen plowing method to produce their crops. The area earns a uni-modal rainfall distribution hence farmers produce crops once a year except some farmers have the possibility to produce twice a year if they can able to produce grain crops that take advantage of residual moisture in clay and clay loamy soils. The agricultural system is generally fragmented in landholding, low agricultural management inputs such as fertilizers, pesticides, uneven rainfall distribution which some of it has erratic nature. The soil of the experimental site is vertisol while the upstream part of this area is cambisol.
Figure : Map of the study location, North Gondar zone, Northern Ethiopia.
Onset and Cessation of Rainy Season The occurrence of rainy seasons and dry spells (within the rainy season) was carried out based on frequency analysis of 46 years (1970-2016) daily weather data.
The onset of rainfall was determined applying the FAO (1978) and Berger (1989) criteria. The FAO (1978)criteria define the onset of rainy season as the time of year when precipitation equals or exceeds 0.5ETc. Consideration was taken to use 15-day period given rainfall within 5 summed to give more or equal to 25mm, and the next 10 days also receive more than 25 mm, then, the first day of the period marks the onset of rainy season. Similarly, rainfall cessation is defined as the first 10 days rainfall below 0.5ETc given the next anymore 10days and above has a decadal rainfall below 0.5ETc.
Dry Spell and Wet Spell Analysis Within the defined rainy season, intra-seasonal the length of dry spells was determined by superimposing actual crop water requirements based on growth stages and transpiration demand over the growth period considering the onset date. Crop coefficient (kc) and number of days in each sorghum growth stage were inferred based on Allen et al., (1998). Frequency analysis of 42 years record yielded exceedance of rainy days. The probability of occurrence of a dry spell exceeding 7, 10, 14, 18and 21days was determined for all days of the year, where one can infer the probability of dry spell since the desire planting date. Dry spells with length of 10days were used following many authors Sivakumar, 1992; Bonsal and Lawford 1999; Huth et al., 2000; Anagnostopoulou et al, 2003; Gong et al., 2005. Besides, 7days 14days and 21 days were selected systematically to align with weeks for crosschecking the climate condition with the soil moisture condition.
To investigate the rainfall and rainfall characteristics and their effect on growth of sorghum in vertisols of the study area, dry spell and wet spell were analyzed based on method followed by Stern et al.
occurre -order Markov chain probability model, first introduced by Gabriel and Neumann (1957), to estimate probability of occurrence of rainfall. It is assumed that rainfall at any given day is a stochastic event only dependent on the
-order process. Each year (Qi) of the dataset can be described as a sequence of dry (xj = 0) or wet (xj = 1) days as:
for
Where i is the number of years and j is the day number of year (DOY). The probability for day being rainy after a day can be estimated.
The probability a rain day after a rainy day can be described with;
Planting Date Historical rainfall data in the study area for 41 years was used to identify the most appropriate planting date. Appropriate planting date is characterized as convenient soil and air temperature, sufficient moisture and oxygen. Soil moisture out of them is the most variable element required to be fixed in the study area. The supply of soil moisture is from a rain whose temporal variability is an obvious. The in- situ soil moisture depends upon various factors of which rainfall intensity, soil infiltration characteristics, slope of the farm, soil depth are the major ones.
Soil physiochemical and Hydraulic Properties Composite soil samples were collected before planting and soil chemical and physical analysis was done at Gondar Soil Laboratory. Soil sampling for analysis was taken from depths of 25cm for organic matter, total nitrogen, exchangeable phosphorus, soil PH, texture, and structure and bulk density analysis. Soil organic matter was analyzed using Walkley-Black method. Total nitrogen was followed Kjeldahl-N, while exchangeable phosphorus was analyzed following Olsen et al.,(1982) procedure.
Soil texture analysis was done followed sieving method following hydrometric method. Soil bulk density was measured using undisturbed soil samples from the study field. Besides to the top 25cm soil profile, a soil depth range of 25-50cm was also taken for soil textural analysis.
Water balance
Soil field capacity, saturation level, wilting point and saturated hydraulic conductivity of the soil was determined from pedo-transfer function after analysis of the soil texture. Water holding capacity of the soil was determined at each root depth and crop coefficient (kc) was determined following sorghum growth stage. Hence, the soil water balance was estimated using the following equation.
Wn = Wn- + Rn - ETC
Where, Wn = Water content of the profile at any day(n), Wn- = water content of the profile one day before nday (n- Rn = the amount of rain of amount greater than 0.85mm at n day. Etc = the crop water requirement of the crop at n day
According to Stroosnijder ( , the maximum amount of water that is extractable for plant roots
cases of dry spell conditions.
The total available water (TAW) in the rootable part of the soil profile is:
Where, RZeffective = effective root zone FC = Field capacity WP = Wilting point p = Allowable depletion level
Rainfall pattern and distribution Daily rainfall data was collected from nearby meteorological stations. Some missed daily rain data were included from adjacent meteorological stations. These data include from 1970 to 2016. Whenever more than 15% of daily data are missed from the annual record between April first and October 30, in or around the stations of study area, they were excluded from analysis. The data were analyzed using INSTAT version 3.37(SternandKnock, 1998) for dry spell occurrence and wet spell probabilities.
Field Experimental Design An on-farm experiment was conducted on sorghum on a vertisol in 2014 and 2015 cropping season to verify surplus water and dry spells so that to select relevant mitigation measures, ridging and tied ridging. Local sorghum variety was sown at the onset of rains (commonly the second week of June). Recommended amount of 46 kg ha- P O and 87 kg ha- N fertilizers were applied equally for each treatment. DAP and Urea fertilizers were used as source to supply phosphorous (P) and nitrogen nutrient respectively. Gross plot size was 5 m x 4.5 m (22.5 m ). Sorghum seeds were drilled in rows at spacing of 75 cm between rows and 15 cm between plants then thinly covered with soil. Weeding was done four times throughout the growing season.
Treatments
Table 1: Treatment codes and treatment name for verification of ridging and tied ridging strategy of vertisols
Trt code At Planting 3weeks latter 6weeks latter
8weeks latter
9weeks latter
12weeks latter
Tied ridge Tied ridge throughout
Ridging Tying Flat Tied ridging Flat Ridging Tied Flat Ridging Tied Flat Ridging Tied Flat Tied-
ridging Flat Flat throughout
N.B. Tied: there was a ridging before, and that ridge was tied after some time as specified on the table, tied riging (columun 5 and row 7) indicates both ridging and tying was done at the same time
- time of tie- his case, tied ridge is the development of raised soil built of fixed dimension where furrows are in both adjacent sides. In cases of tied ridges, furrows are blocked with soil built so that water will pond for a while which allows infiltration in to sub-soils. Flat, in this case, represents the traditional
Ridging and Tied ridging
practice of tillage where slightly rough undefined till lines are developed with oxen plow.
35c m
Furro (a)
Figure 2: (a) Schematic of ridging; (b) Ridging, furrows and tied ridging
Tie-ridging was developed with 20cm depth and 75cm apart and tied at intervals of 2m during and after planting based on the time fix of each treatment. Height of ridges was 15cm while gradient of the furrows was 1%, so that less erosive flow of excess rain. Sowing was done on the ridges only for the treatments with ridging and tied ridging.
Soil moisture and weather monitoring
Soil moisture was monitoring in weekly basis using gravimetric method on morning at day time between 9:00 12:00AM. Soil sampling was done at soil depths of 0-20cm, 20-40cm for water content analysis. After weighing the wet soil sample using 0.01gm sensitivity electronic balance, it was taken to an electric oven and dried to 105oc for 24hours. After the oven drying, samples were weighed immediately after withdrawal from the oven. Subsequently, the gravimetric soil water content (SWC) was determined using the following equation:
Where, g = gram
Ridges Furrows
Tie ridge
2
(b)
RESULTS AND DISCUSSION
Figure First order Markovchain rainfall probability occurrence in Gondar-zuria areas
As shown in figure4, high probability of wet spell occurrence is obvious between day numbers of 181 and 231, which accounts to probability value between 0.70 and 0.73. At this period sorghum have a development stage where the effective root zone approaches 1meter.
Figure 5: probability of dry spell occurrence
As shown in fig.5, a probability of dry spell with length of 7days and more is very insignificant if the usual start of the rain season is from June first (DOY of 150).Besides, if the cessation of the season is around mid of September (DOY of 256), the probability of dry spell occurrence with length of 7days is around 10%. The study has considered dry spell length 7days and more which matches the soil water holding capacity in cases of rainfall delay. Barron et al. (2003) consider a dry spell between 5 15 days to be harmful for sub-Saharan Africa.
Appropriate Planting Date, Ridging, Tied Riding Field capacity of the soil was estimated to be 170mm/m of which 102mm/m is available to crops. During planting, the surface soil where to plant sorghum has to meet enough soil moisture, 17mm to
soil depth of 10cm. Besides, the soil should maintain its available water through its all growth periods with no significant dry spell periods. According the above specified criterion, the following specification was set to select an appropriate planting date for sorghum.
Exploring time of ridging Choosing the appropriate time of ridging depends upon objective of ridging that is to plant the crop on the ridges, hence, to escape from logging water. Depending on the planting date and rainfall amount, the ridging time can be fixed in such a way crops can escape from excess logged water on vertisols for growth period without an interruption of dry spells at some probability level.
Figure 6: Appropriate planting dates based on rainfall record (1970 to 2016)
Average planting date, as defined in fig.6, is June 9 (days of the year (DOY) 161) to June 13 (DOY 165). This is supported with a result in fig.7, which shows a relative frequency of 70% years from the
t. But, based on fig. 7, one can understand that more than 90% of the sample years own a decadal rainfall which is 25mm more than the decadal crop water requirement in dates between 28th June (DOY 180) and 27th August (DOY 240). Despite the negative effect the excess water have on crops grown in areas with poorly draining soils, decadal rainfall amount 50mm more than decadal crop water requirement is documented on 80% to 90% of the sampled rainfall in between these dates. Based on this pre-request, ridging must be practiced each year between 28thJune (DOY 180) and 27th
experiment had treatments which align to these days. Fig.4 shows the probability of a day with rain day, between (DOY 180) and (DOY 240) ranges from 0.72 to 0.65.
Both the amount and frequency of rainfall events contribute for the total amount of water on a specific field. Concurrently, days of the year between 180 and 240 have both higher probability of day with rain day (fig.4) and higher decadal rainfall which exceeds 25mm to 150mm more than decadal crop water requirement (fig.7).
Figure 7: Relative frequency of excess rainfall at different exceedance levels
Soil Physiochemical and Hydraulic Properties of the Study Area Soil texture of the study area is clayey which has cracking and swelling nature during dry and wet soil conditions; and general slope of the field is about 1%, while it soil depth is more than 1meter.
Table2:Soil physiochemical characteristics of the study area
Soil depth (cm)
- Blocky Clay - Blocky - - - - - Clay
Soil water balance After assessing the most frequent daily crop evapo-transpiration, figure 8 which shows the soil water balance, was developed.
Table 3: Soil textural and hydraulic properties of study area based on Saxon
Soil depth (cm)
Field capacity
Wilting point
- Clay
- Clay - - - -
According to the soil moisture table 3, the wilting point fraction is 0.26 and field capacity fraction of 0.43. Therefore for soil depth of 1meter, the soil has water holding capacity of170mm/m:
Figure 8: Most frequent evapotranspiration of sorghum in 2015
Considering the extension of sorghum root depth to 1meter in average, where majority of roots soil water extraction is held, the roots can extract an amount of water calculated using:
Hence RAW = 102 mm/m. With an estimated evapotranspiration (ETo) of 5 mm, this implies that the reserves of water for a crop as described above are sufficient for a dry spell of 20 days, approximately 3 weeks. Indeed, this is only the case if the soil moisture content was fully replenished at the start of the dry spell and roots are capable of extracting full water up to this depth. But, this is not practical since the mass distribution of the roots decreases down the soil profile.
Figure 9: Rainfall and readily available soil water of the study area in 2015 summer growth season
Fig.9 shows the soil water which is available for crops is more than the requirement of sorghum DOY 193 to DOY 240 that corresponds from start of July to end of August. These months match with the
forecasted months of possible wet spell occurrence, according daily rainfall data of years 1970 to 2016 (fig.7).
To evaluate efficiency of treatments with ridging and tied ridging time, fig. 10 tried to show the soil water content of these treatments during dry spell and wet spell conditions. Accordingly, t2 which has ridge planting up to DOY 195 had comparatively lower soil moisture content in the wet period, where water logging is expected. Besides, this treatment had comparatively higher soil water content when dry period prevails, i.e end of September to end of October. During these periods, end of September to end of October, sorghum demands higher water due to its morphological stage and higher atmospheric water demand (fig.10).On the other hand, t5 has optimum soil moisture during the wet period and higher soil moisture a week after the start of dry spell day. This may attribute from tied-ridging ahead of the first date of dry spell and better performance of the crop (table 4 and table 5).
Figure 10: Soil water content (%) on soils of each treatment, decadal ETc and rainfall of study area
During soil moisture record, the rainfall distribution is shown as in fig.11. As shown in this figure, there is a dry spell period (from DOY of 265 to 304 corresponding to dates from 21st September to 30 of October respectively) for about 40days. On these days the soil moisture may get depleted to the level crops hardly extract water even to the possible soil depth of about 2meters. As shown in fig. 6, the study crop, sorghum, has high water demand on this time interval. Therefore, the treatments which support soil moisture conservation for further use during lengthy dry spell period should be evaluated.
Theoretically, tied ridge encourages the replenishment of soil with water. Therefore, all treatments employed with tied ridges before the arrival of longer dry spell, must realize comparatively higher soil moisture than the open ridges given that there is no need of tying these ridges during excessive soil wetting. Based on deterministic method, the daily rainfall distribution of 2015, as shown in fig.11, shows longer dry spell after DOY 265 where there is a need of tied ridging before this wet spell day to maintain enough soil moisture during the dry spell period. But, the return period of this rainfall distribution may very low. Therefore, the stochastic method of determining the possible wet period, as shown in fig.7, well argue on the appropriate time of tied ridging. As a result, the observed dry spell period in 2015 late rain season has probability value more than 40%.Hence, to minimize the loss of crop yield due to dry spell longer than 7days, tied-ridging practice is required before the probable reset
Trt Weeks of ridging/tying the ridge after planting
planting 3 6 8 9 12
t1 Tied ridge
t2 Ridge Tying t3 Flat Tied ridge t4 Flat Ridge Tying
t5 Flat Ridge Tying t6 Flat Ridge Tying t7 Flat Tied ridge t8 Flat
Figure 11: Rainfall distribution and weeks of ridging and tied ridging practice in 2015 rain season
Time Of Ridging And Tied-Ridging, And Soil Moisture Variability According fig.13, higher minimum soil moisture was observed in t1 (tied ridging throughout) and t8 (flat throughout) in the top 0-20cm soil profile. The higher minimum soil moisture is, may be, due to longer stay of water without get drained. These two treatments have lower coefficient of variation among the observed soil moisture contents in the soil depth 20-40cm. The higher soil moisture is attributed from the tied-ridging throughout and flat throughout for t1 and t8 during moisture sampling. Soil moisture sampling result shows a range of soil water content (%) from above field capacity to wilting point. In drainage problematic soils, it is obvious that soil water status stays above field capacity for more than 24hours after effective rain. The soil water content result of some samples (fig.12)proves this argument.
Figure 12: Soil water content extreme values with their respective coefficient of variation (CV)
As presented in fig.12, the change of soil moisture at the upper soil profile (0-20cm) is dynamic due to its exposure to the atmosphere, where wet and dry atmospheric conditions simply affect the top soil layers soil moisture level. At 20-40cmsoil depth range, the practices of ridging and tied ridging increased soil water status because of the opportunity time variation for water infiltration. If the ridge is tied before the excess rainfall event, water pond may allow increasing cumulative infiltration. The cumulative infiltration further wet the soil layer beneath the top soil layer. Soil moisture, already reserved beneath the top (0-20cm), helps the crop roots to extract water from this reserve at drying conditions.
arise from the fact that the treatments with open ridges and tied-ridges may faced to quick drying and wetting during dry day and wet day respectively. In contrary, during excess rainfall where water logging may occur in the soil, open ridges may allow removal of the standing excess water out of
upper root areas.
Effect of Ridging and Tied-ridging on Sorghum Yield
Table 4: Effect of ridging and tied-ridging strategies on yield and yield components of sorghum; for years of 2014 and 2015
Treatment code
N.B. Treatment means with same letters are not significantly different at significance level (5%), treatments with different letter are significantly different at 5% significant level.
sorghum as affected with ridging and tied-ridging treatments.
In 2014 growing season, summer season in this case, both stover yield and grain yield were affected with the treatments. Specifically, except t1 and t2, where tied ridging was carried out throughout the wet period, there is no significant yield variation among the other treatments, which gave comparatively higher stover and grain yield.
Furthermore, in 2015 growing season, similar grain yield to that of 2014 was observed while stover treatments. Two years (2014 and 2015) combined result
showed ridging and tied- for 2014 yield.
Table 5: Effect of ridging and tied-ridging timing on yield and yield components of sorghum; for year 2016and combined years (2014, 2015, and 2016)
Treatment code Combined (2014, 2015, 2016)
Stover yield ton/ha
Grain yield ton/ha
Stover yield ton/ha
Grain yield ton/ha
LSD (0.05) ns ns
The 2016 growing season yield result was not affected with the ridging and tied-ridging timing (table 5). Besides, combining 2016 growing season yield result (table 5) with the 2014 and 2015 (table 4)
d result of 2014 and 2015.
CONCLUSION
This study has tried to investigate the probability of dry spells which were found to be in the flowering and maturity stage, while the probability of wet spells that may cause water logging for vertisol at flat fields for water logging sensitive crops. In this regard, excess rainfall (beyond evapo-transpiration need of the crop) was found to be more recurrent an example after 20 days of planting, the rainfall with various exceeding levels after the decadal crop water requirement. Total of 36 years data was used to contrast the decadal evapo-transpiration needs of crops with the decadal rainfall. It was found that some weeks after the planting; various exceeding levels were identified such as more than the mean decadal evapo-transpiration need, 1.5, 2, 2.5 and 3 times more than the mean decadal evapotranspiration need.
In the sample year, 2015 summer growing season, there were both occurrences of wet spells and dry spells with greater than 10days at initial to development and flowering to maturity stage. Despite better tolerance capacity of the crop at maturity stage due to deep rooted nature, there is a probability of dry spell to a value of more than 0.4.
Ridging at planting may expose a root zone for drying incase of short dry spells. But, if there is high probability of raining at and few days after planting, this riding practice is highly important since the top soil layer where the roots may have concentrated is highly vulnerable for water logging problems. In th during this stage have imperative implication for the overall growth of the crop.
In conditions of extreme wetting and drying periods, ridging and tied ridging practices normalize the
variation soil water content of the soil.
The yield indeed does not have clear indication on the impact of riding and tied ridging on the yield of sorghum. This may have resulted from the fact Nitrogen fertilizer application which reduces the impact of water logging on sorghum growth (Heluf, 2003).However, the combined yield result showst5 has comparatively higher mean grain yield. This result supports to the theoretically determined time of
cropping -40cm root depth.
Accordingly, this study reveals the optimum time of ridging and tied-ridging period for sorghum growth in North Gonder near and around Gonder zuria wereda. Therefore, for sorghum cropping in the study area, flat at planting and ridging 3 weeks later then tying the ridge 9weeks after planting is recommend to allow the crop an optimum root soil moisture status. This study also recommends further
investigation to be conducted if fertilizer amount reduce the effect of water logging on sorghum
ACKNOWLEDGEMENT
We strongly acknowledge for the Gondar Agricultural Research Center staff who directly or indirectly shared valuable contribution for this study. We also urge to show a gratitude to the Gondar-zuria wereda experts, farmers and other stakeholders who contributed their meaningful efforts to accomplish this study. Last but not least, our great thank goes to ICARDA (International Center of Agricultural Research for Dry Areas) for its financial and technical help and ADC (Austrian Development Cooperation) for supporting this research activity financially.
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