ELSEVIER Agriculture, Ecosystems and Environment 61 (1997) 59-67

Agriculture Ecosystems & Environment

Energy-use patterns in sub-tropical rice-wheat cropping under short term application of crop residue and fertilizer

Apurba Sarkar System Management Section, Project Directorate for Cropping Systems, Research, Modipuram, Meerut 250 110 (UP). India

Accepted 23 May 1996

Abstract

Rice-wheat cropping in the sub-tropics is energy intensive, requiring a major input from fossil fuel. These crops produce lots of residue, part of which is often wasted in burning, the incorporation of which is beneficial when applied with fertilizer. Reserves of fossil fuel is decreasing at an increasing rate. Therefore, it is more important to know the effect of application of residue production from these crops in the light of recycling of energy and its output. Keeping this in view in a field experiment between 1990 and 1992, three levels of residue incorporation: (i) nil, (ii) half, (iii) full of residue production from one crop to the other were combined with two levels of mineral fertilizer: (i) no fertilizer, (ii) standard level of 120, 60, 60 kg N, P205 and K20 per hectare as treatments. The trade-off studies showed that applications of half the crop residue with fertilizer consistently produced the highest grain yield of rice and wheat. Addition of residue without fertilizer had little benefit while application of fertilizer without residue had moderate effects. The combined application of half the residue with fertilizer proved to be the best combination providing the maximum production of crop per unit use of fossil fuel.

The highest labour productivity (crop production/hour of labour) was also found under the same treatment. But further addition of residue with fertilizer declined the crop production per unit area, per unit of fossil fuel or per hour of labour. So keeping in view the fast depleting commercial energy sources, incorporating half the residue production of the crop with recommended fertilizer in a rice-wheat cropping may be a wise practice in solving the energy problem for higher production in this part of the subtropics.

Keywords: Energy; Sub-tropics; Rice; Wheat; Crop residue; Fertilizer

1. Introduct ion

From time immemorial , the human being had been using energy from renewable sources. With population pressure, it turned towards non-renewable sources like fossil fuel. Its reserves are dwindling rapidly and their prices are sky-rocketing. By the turn of the century, world population will be around six billion. We can expect that fossil fuel dependant crop production technology will experience increas- ing difficulty in feeding such teeming billions. So

human should reduce the dependency of food supply on fast disappearing oil stocks, more so far a popu- lous nation like India. It is estimated that by 2000 AD India will require 1370 X 106 GJ of energy for its crop production of which 880X 106 GJ will come from commercial source and 490 x 106Gj from non-commercial sources (Pal et al., 1985). Naturally, it is imperative to look into the trade-offs related to the source of energy for crop production. In this respect, crop residue shows high promise as renew- able source of energy. To study such trade-offs use

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60 A. Sarkar / Agriculture, Ecosystems and Enoironment 61 (1997) 59-67

in this paper, the following parameters: (i) crop yield per unit area; (ii) dependency of crop supply on fossil energy measured in kg of crop produced per MJ input of fossil energy; (iii) productivity of labour measured in kg of crop per hour of labour are considered. Crop yield may be measured both in term of kg grain/ha or kg of total biomass (grain + straw)/ha.

Rice-wheat cropping shares a major part of com- mercial energy in India (Singh et al., 1990). Both the crops produce a lot of crop residue, a part of which is wasted in burning. However, a number of workers like Gotah and Onikuru (1991), Mishustin et al. (1975), Hwang et al. (1989), Will et al. (1989), Wold et al. (1989), Verma et al. (1989) and Stott et al. (1990) have reported the good effect of crop residue application in rice-wheat cropping. Usually incorpo- ration of such residue is beneficial in the long run (i.e., after a number of seasons of residue addition, say six or more) particularly in combination with fertilizer (Vlek, 1990). But reserve of fossil fuel is declining at a faster rate. So it is more important to know whether there is a short term (i.e., after one or two seasons of residue addition) effect of application of residue production from these crops at all in the light of recycling of energy and its output. Keeping this in view the present programme was initiated.

2. Materials and methods

During 1990-1992, the experiment was con- ducted on a sandy loam soil (Helpludult), at the Project Directorate for Cropping Systems Research, Modipuram (29°4'N, 77°46"E). The pH of the soil was 8.0 (1 soil: 2.5 water). It has 1.58 g m /cm 3 bulk density, 4 m eg /1 0 0 g m CEC (Cation Exchange Ca- pacity), 0.38% organic carbon, 12ppm available P and 90 ppm available K. Six treatments (see Table 1 for details) were tested in a randomised block design with four replications. Straw at harvest of crop be- came the crop residue for the succeeding crop. Min- eral P (single super phosphate), K (Muriate of potash) and residue were broadcast before planting and ploughed down to 20 cm depth. Urea N (46% N) was given in three dressings, half at sowing, 1 /4 30d after and the rest after 45 d of sowing. The rainfall was 700mm during the growing season of 1990- 1991 and 685 mm 1991-1992 respectively. Rice cul- tivar 'Govind' was directly seeded on 15th July each year @ 120kg seed/ha in rows 20cm apart. It was harvested on 2nd November, 1990, 1991. Wheat cultivar HD-2285 was sown on 20th November 1990 and 1991 @ 120kg seed/ha in rows 20cm apart. It was harvested on 22nd April, 1991, 1992. Rice and wheat were given 8 and 5 irrigations respectively.

Table 1 Description of treatment chosen for rice and wheat

Treaments On rice

Crop residue Mineral fertilizer of previous (kg/ha)

wheat crop N P205 K20

On wheat

Crop residue Mineral fertilizer of previous (kg/ha)

rice crop N P205 K20

1. Central (No crop residue and no mineral fertilizer) 2. Half residue-alone Half (Half the residue added) 3. Full residue-alone Full (Only full of the residue added) 4. Fertilizer-alone (Only mineral fertilizer added) 5. Half residue-fertilizer Half (Half the residue added with mineral fertilizer) 6. Full residue-fertilizer Full (Full of the residue added with mineral fertilizer)

120 60 60

120 60 60

120 60 60

Half

Full

Half

120 60 60

120 60 60

Full 120 60 60

A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67 61

Table 2 Equivalents for different sources of energy used in energy calcula- tions

Source of energy Unit Equivalent energy (M J)

Human labour hour 1.96 Seed (rice, wheat) Kg 14.70 Crop residue (straw of rice, wheat) Kg 12.50 Diesel Litre 56.31 Fertilizer Nitrogen Kg 60.00 P205 Kg I 1.10 K20 Kg 6.70 Chemicals a. Superior chemicals Kg 120.00 b. Inferior chemicals Kg 10.00 C. Machinery Electric motor Kg 64.80 Prime movers (other than Kg 68.40 electric motor) Farm machinery Kg 62.70

Source: Mittal et al. (1985). a. Materials requiring dilution at the time of addition. b. Materials requiring no dilution at the time of addition. c. Assuming that the use of the machinery occurs equally over the total life span of the machinery (in hours).

The fuel consumed for a particular field operation in the case of tractor or engine was measured by top-filled method. Irrigation, threshing, removal or incorporation of residue were done through diesel operated engine. For trade-off parameters: The grain and straw yield at harvest are reported in kg/ha; dependency of crop supply on fossil fuel energy is measured in kg of grain or biomass (grain + straw) per MJ of fossil fuel used in production; productivity of labour is measured in kg of grain or biomass (grain + straw) per hour of labour. The energy equivalents used for energy calculation are given in Table 2.

3. Results and discussion

3.1. Crop yield (grain, residue and biomass)

Application of residue (half or full) or fertilizer alone increased the rice grain yield compared to that of control, but significantly so with the application of only the fertilizer (Table 3). A combination of half

Table 3 Crop yield (grain, straw and biomass) of rice and wheat under different treatment

Treatment

Rice 1990 Wheat 1990-1991

Grain Residue Biomass Grain Residue Biomass yield yield yield yield yield yield (kg/ha) (straw) (grain + straw) (kg/ha) (straw) (grain + straw)

(kg/ha) (kg/ha) (kg/ha) (kg/ha)

Control 2400 1860 4260 1500 1640 3140 Half residue-alone 2900 2380 5280 1600 3026 4626 Full residue-alone 3300 2640 5940 1700 3016 4716 Fertilizer-alone 4700 3810 8510 3000 3710 6710 Half residue-fertilizer 5800 4620 10420 3700 4380 8080 Full residue-fertilizer 4800 3770 8570 3000 4320 7320 C.D.5% 1000 672 1798 550 560 1194

1991 1991-92 Control 1850 1870 3720 1200 2490 3690 Half residue-alone 2470 2560 4970 1300 3060 4360 Full residue-alone 2700 2770 5470 1500 3170 4670 Fertilizer alone 4660 4820 9480 4000 6740 10740 Half-residue ferti. 5700 6290 11990 4800 8110 12910 Full residue-fertilizer 4800 4880 9600 4500 8000 12500 C.D. 5% 800 982 1625 750 1202 2155

N.B. Wheat residue yield before the 1990 rice were 1500, 3006, 3006, 3604, 4360 and 4310 kg/ha, respectively for the six treatments, which were added accordingly before the sowing of 1990 rice.

62 A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67

Table 4 Operational energy requirement for raising upland direct seeded rice and wheat under different treatments

Operations Energy equivalents (MJ ha- J

Rice Wheat

Seedbed preparation 1225 1226 Sowing 251 251 Irrigation 11605 7253 Weeding 565 282 Fertilizer application 63 63 Harvesting 251 251 Threshing 1273 1273 Transportation 153 153 Post harvest activities 29 29 Total 15415 10781

The corresponding energy under control is 15399 and 10765MJha-~ for rice and wheat respectively.

the crop residue and fertilizer markedly increased the grain yield over all other treatments. But application of full residue with fertilizer significantly declined the yield. Rice residue and biomass yield followed the similar trends.

Similar trends were also noted in case of wheat crop yield (i.e., grain, residue and total biomass).

3.2. Operation-wise energy requirement

The total operational energy requirements were 15415 and 10781MJ/ha (Table 4) for rice and

wheat, respectively. Rice required more because of more energy consumption in irrigation and weeding compared with wheat. Irrigation required the highest energy for both the crops (75%, 67%) followed by threshing (8%, 11%) and seed-bed preparation (8% and 11%), It is worth mentioning here that rice was grown under irrigated upland condition and required 8 irrigations against only 5 for wheat. The operations like irrigation and threshing required diesel operated pump or machinery. Energy consumption for control treatment was a bit less in the absence of fertilizer application.

3.3. Source-wise energy requirement

Tables 5 and 6 contains a detailed source-wise energy requirement under different treatments. For check plots, diesel fuel required the largest energy input followed by seed in both the crops. Crop residue required the largest input energy followed by diesel fuel in residue treated, plots, more when the entire quantity of residue was added than only half the residue addition. When fertilizer was the only treatment, diesel required the largest share of input energy for both the crops followed by fertilizer. Crop residue again required the largest input energy fol- lowed by diesel and fertilizer in residue plus fertil- izer treated rice and wheat plots, more in full residue fertilizer plots than in half residue-fertilizer plots. So

Table 5 Source-wise input energy requirements for rice under different treatments

Treatments Energy equivalent (MJ ha- 1 ) rice 1990

Human Seed Diesel Fertilizer Crop residue Chemicals Machinery

Control 1349.5 Half-residue-alone 1365.3 Full residue-alone 1365.5 Fertilizer-alone 1366.1 Half-residue-fertilizer 1366.5 Full residue-fertilizer 1366.1

1991 Control 1349.5 Half-residue-alone 1365.3 Full-residue-alone 1365.5 Fertilizer-alone 1366.3 Half-residue-fertilizer 1367.3 Full-residue-fertilizer 1366.5

1764 13441 1764 13745 18787 1764 13754 37575 1764 13799 8340 1764 13828 8340 27250 1764 13796 8340 53875

1764 13447 1764 13751 18912 1764 13756 37700 1764 13807 8340 1764 13858 8340 27375 1764 13813 8340 54000

150 150 150 150 150 150

150 150 150 150 150 150

396 396 396 396 396

396 396 396 396 396 396

A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67 63

four important input energy sources were found namely, crop residue, diesel, fertilizer and seed. But wherever crop residue was involved, it required the highest share of input energy. For, added quantity of crop residue far exceeded those of other inputs. And it was more so when the entire quantity was added either alone or in combination with fertilizer.

3.4. Parameters for studying the trade-offs: Kg crop / MJ of fossil fuel

Check plot (Table 7) produced 0.178 and 0.138 kg rice grain/MJ of fossil fuel used in 1990 and 1991, respectively. Applications of crop residue (half or full) alone did not make much difference contrasting to that of applying only the fertilizer (0.341 and 0.338). But application of half the crop residue with fertilizer consistently increased the rice grain yield per MJ of fossil fuel used (0.419 and 0.411, respec- tively in 1990, 1991) comparing those of all other treatments. But applying full of the residue produc- tion with fertilizer significantly declined it.

Application of half the crop residue with fertilizer was markedly the most economic user of fossil fuel producing more biomass (0.136 and 0.178kg more/MJ of fossil fuel used) than produced apply- ing only the fertilizer. Such crop production per unit expenditure of fossil fuel declined with the applica- tion of fertilizer with entire quantity of the residue.

The wheat crop showed similar trends in this respect. Wheat check plot produced 0.162 and 0.130kg grain per unit expenditure of fossil fuel in 1990-1991 and 1991-1992, respectively. Crop residue addition alone made only marginal difference unlike applying only the fertilizer (0.314 and 0.417). But obviously, the combined application of half the residue and fertilizer outshone all other treatments combinations. It produced 0.072 and 0.085 kg more wheat grain/MJ of fossil fuel than produced apply- ing only the fertilizer in 1990-1991 and 1991-1992, respectively. Of course, applying the entire residue with fertilizer had little benefit. Wheat biomass yield/MJ of fossil fuel also followed the same trends.

3.5. Labour productivity

Rice check plots had the least productivity of labour (Table 7) producing only 3.5 and 2.7kg grain/hour of labour in 1990 and 1991, respectively. Application of only the residue (half or full) had little effect contrasting to applying only the fertilizer (6.8 and 6.7). But application of half the crop residue together with fertilizer was the most economic in the use of labour producing 8.3 and 8.2kg rice grain/hour of labour during 1990 and 1991, respec- tively. Application of the entire residue with fertil- izer, however had no further benefit. Labour produc- tivity in terms of rice biomass yield had the similar

Table 6 Source-wise input energy requirements for wheat under different treatments

Treatments Energy equivalent (MJ ha - I ) wheat 1990-1991

Human Seed Diesel Fertilizer Crop residue Chemical Machinery

Control 1019.9 1764 9212 Half residue-alone 1036.5 1764 9544 14875 Full residue-alone 1036.3 1764 9533 33000 Fertilizer-alone 1036.8 1764 9597 8340 Half-residue fertilizer 1037.2 1764 9595 8340 28875 Full residue-fertilizer 1037.0 1764 9584 8340 47125

1991-1992 Control 1020.4 1764 9229 Half-residue-alone 1036.5 1764 9544 15625 Full-residue-alone 1036.5 1764 9539 34625 Fertilizer-alone 1037.0 1764 9589 8340 Half residue-fertilizer 1038.0 1764 9640 8340 39313 Full residue-fertilizer 1037.4 1764 9601 8340 61000

150 150 150 150 150 150

150 150 150 150 150 150

314 314 314 314 314 314

314 314 314 314 314 314

64 A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67

Table 7 Kg of c rop /MJ of fossil fuel and productivity of labour (kg c rop /h of labour) in rice and wheat under different treatment

Treatment Rice 1990 Wheat 1990-1991

Kg of c rop/MJ of fossil Kg of c rop /h of Kg of crop/MJ of fossil Kg of c rop /h of fuel labour fuel labour

Grain Biomass Grain Biomass Grain Biomass Grain Biomass

Control 0.178 0.316 3.5 6.2 0.162 0.341 2.9 6.1 Half-residue-alone 0.211 0.384 4.2 7.6 0.167 0.485 3.0 8.8 Full-residue-alone 0.229 0.432 4.7 8.5 0.178 0.495 3.2 8.9 Fertilizer-alone 0.341 0.617 6.8 12.2 0.314 0.701 5.7 12.7 Half-residue-fertilizer 0.419 0.753 8.3 14.9 0.386 0.842 7.0 15.3 Full-residue-fertilizer 0.347 0.621 6.9 12.3 0.313 0.764 5.7 13.8 C.D. 5% 0.072 0.132 1.42 2.55 0.061 0.133 1.1 2.38

1991 1991-1992 Control 0.138 0.277 2.7 5.4 0.130 0.400 2.3 7.1 Half-residue-alone 0.179 0.361 3.5 7.2 0.136 0.457 2.5 8.3 Full-residue-alone 0.196 0.397 3.8 7.8 0.157 0.489 2.8 8.8 Fertilizer-alone 0.338 0.687 6.7 13.6 0.417 1.120 7.6 20.3 Half-residue-fertilizer 0.411 0.865 8.2 17.2 0.497 1.339 9.1 24.4 Full-residue-fertilizer 0.347 0.695 6.9 13.8 0.469 1.302 8.5 23.6 C.D. 5% 0.050 0.178 1.2 2.76 0.078 0.229 1.4 4.13

trends. Such productivity of half-residue fertilizer plots was the highest (14.9 and 17.2 kg biomass/hour of labour).

In case of wheat, 2.9 and 2.3 kg wheat grain/hour of labour were noted in check plots during 1990- 1991 and 1991-1992, respectively. Most economy in labour use was noted when half the residue was applied with fertilizer (7.0 and 9.1 kg wheat

Table 8 Source-wise biophysical inputs for rice under different treatments

grain/hour of labour, respectively in 1990-1991 and 1991-1992). Further benefit was not found in the economy of the labour use when the entire residue was applied with fertilizer. Labour productivity in terms of wheat biomass yield had the same trends as for grain. Significantly the most economic use of labour was found with the application of half the residue coupled with fertilizer (15.3 and 24.5kg

Treatments Input per hectare on rice, 1990

Human (h) Seed (Kg) Diesel (1) N Fertilizer (Kg) Crop Chemical Machinery

P205 K 20 residue BHC (Kg) Tractor (h) Pump (h)

Control 688.5 120 238.7 Half-residue alone 696.6 120 244.1 1503 Full-residue alone 696.7 120 244.3 3003 Fertilizer-alone 697.0 120 245.1 120 60 60 Half-residue-fertilizer 697.2 120 245.6 120 60 60 2180 Full-residue-fertilizer 697.0 120 245.0 120 60 60 4310

1991 Control 688.5 120 238.8 Half-residue-alone 696.6 120 244.2 1513 Full-residue-alone 696.7 120 244.3 3016 Fertilizer-alone 697.1 120 245.2 120 60 60 Half-residue-fertilizer 697.6 120 246.1 120 60 60 2190 Full-residue-fertilizer 697.2 120 245.3 120 60 60 4320

15 15.50 160 15 17.64 160 15 17.70 160 15 18.02 160 15 18.22 160 15 18.00 160

15 15.50 160 15 17.67 160 15 17.73 160 15 18.05 160 15 18.55 160 15 18.20 160

1. Life span of each piece of machinery is assumed to be 15000h.

A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67 65

wheat biomass/hour of labour during 1990-1991 and 1991-1992, respectively).

3.6. Appraisal of the experiment

Incorporation of only the residue either half or full increased the yield of rice (560 or 825Kg more/ha) and wheat (100 or 250 Kg more/ha) grain (Table 3) than that of its removal (in check plot), but less than that of fertilized plot (fertilizer alone, 2555 Kg more rice and 2150Kg more wheat/ha over the check plot). Residue incorporation (residue only) might have encouraged immobilization of available plant nutrients in soil (specially N) due to enhanced microbial activity leading to low crop yield. This has also been reflected on Kg crop/MJ fossil fuel and on labour productivity (0.8, 1.2, 3.6 Kg more of rice grain/hour of labour and 0.15, 0.4, 4.1 Kg more of wheat grain/hour of labour as resulted from the incorporation of half of residue, full of residue and applied fertilize over the check plot yield (Table 7). In contrast, application of fertilizer had a direct effect on crop yield enhancing it to a great extent.

But the superiority of the addition of half the residue with fertilizer may be caused by synergistic effect of that much amount of crop residue (i.e., half) and fertilizer. This resulted in higher grain produc-

tion (3065Kg more of rice and 2800Kg more of wheat/ha) than when half the residue was applied alone or 1070Kg more of rice and 750Kg more of wheat/ha than when fertilizer was applied alone. Corresponding values of Kg crop/MJ fuel and labour productivity are also associated with those of grain yield. Thus in this experiment residue (half) applied with fertilizer was beneficial under short term appli- cation (2 seasons in this case) while it benefits usually in the long run (after six or more seasons) as reported by others (Vlek, 1990). Note that under this combination (half residue-fertilizer) averagely only 2.19 and 2 .7t /ha crop residue were added to rice and wheat respectively. This means only a marginal addition of plant nutrients. So improvement must have come through better physico-chemical condi- tions of soil like bulk density, water holding capac- ity, porosity, organic matter content, soil tempera- ture, soil biology, etc (monitoring not done in this experiment since it deserves detailed study in a separate experiment).

Marginal differences between removal (followed by burning) and incorporation of residue (either half or full) in terms of labour and fuel consumption are noted (Tables 8 and 9). The residue production under these treatments varied between 2.4 to 6.2 t /ha for rice and 3-8 t / ha for wheat (Table 3) respectively.

Table 9 Source-wise biophysical input for wheat under different treatments

Treatments Input per hectare on wheat 1990-1991

Human (h) Seed (kg) Diesel (1) Fertilizer Crop residue Chemical Machinery

N P205 K2 ° (kg) BHC(kg) Tractor(kg) Pump(kg)

Control 520.4 120 163.6 Half-residue-alone 526.8 120 169.5 Full residue-alone 528.7 120 169.3 Fertilizer-alone 529.0 120 169.9 Half-residue-fertilizer 529.2 120 170.4 Full-residue-fertilizer 529.1 120 170.2

1991-1992 Control 520.6 120 163.9 Half-residue-alone 528.8 120 169.5 Full-residue-alone 528.8 120 169.4 Fertilizer-alone 529.1 120 170.3 Half-residue-fertilizer 529.6 120 171.2 Full-residue-fertilizer 529.3 120 170.5

15 15.44 100 1190 15 17.80 100 2640 15 17.74 100

120 60 60 15 18.00 100 120 60 60 2310 15 18.17 I00 120 60 60 3770 15 18.15 100

15 15.58 100 1250 15 17.8 100 2770 15 17.75 100

120 60 60 15 18.08 100 120 60 60 3145 15 18.61 100 120 60 60 4880 15 18.30 100

1. Life span of each piece of machinery is assumed to be 15000 h. Wt of tractor = 2500 kg. Wt of pump = 320.kg. So for energy calculation viewpoint, the input energy from machinery ranged between 2.58 to 3.09 for tractor and 3.36 kg for pump, respectively for rice in both the years and the corresponding figures for wheat were between 2.57 to 3.10 and 2.1 kg.

66 A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67

Table 10 List of fanning activities in the field for removal (followed by burning) of residue, incorporating half residue, incorporating full residue

Treatment Farming Activities

Removal followed by burning) of residue Incorporating residue Total

Human (h) Fuel (1) Human (h) Fuel (1) Human (h) Fuel (1)

Control 0.5 1.25 0.50 1.25 Half-residue alone 0.32 0.8 0.32 0.8 0.64 1.60 Full residue-alone 0.70 1.75 0.7 1.75 Fertilizer alone 1.02 2.55 1.02 2.55 Half residue-fertilizer 0.62 1.55 0.61 1.53 1.22 3.08 Full-residue-fertilizer I 2.5 1 2.5

Rice, 1991 Control 0.5 1.25 0.5 1.25 Half residue-alone 0.34 0.85 0.33 0.83 0.67 1.68 Full residue-alone 0.73 1.83 0.73 1.83 Fertilizer-alone 1.05 2.7 1.05 2.7 Half residue-fertilizer 0.72 1.8 0.83 1.8 1.55 3.6 Full-residue-fertilizer 1.2 2.8 1.2 2.8

Wheat 1991-1992 Control 0.44 1.1 0.44 1.1 Half-residue-alone 0.4 1 0,40 1.0 0.80 2 Full residue-alone 0,74 1.8 0.74 1.8 Fertilizer-alone 1.0 2.45 1.0 2.45 Half-residue-fertilizer 0.59 1.48 0,58 1.45 1.17 2.93 Full-residue-fertilizer 1.15 2.7 1.15 2.7

Wheat 1991-1992 Control 0.58 1.45 0.58 1.45 Half-residue-alone 0.41 1.03 0.4 l 0.81 2.03 Full-residue-alone 0.75 1.9 0.75 1.9 Fertilizer-alone 1.08 2.8 1.08 2.8 Half-residue-fertilizer 0.75 1.9 0.86 1.82 1.61 3.72 Full-residue-fertilizer 1.3 3 1.3 3

Since the work (incorporation or removal) was per- formed by a human driven tractor in this experiment in a small scale (small experimental plots), the labour and fuel consumption differed only marginally for such operation (see Table 10 regarding farming ac- tivities for removal and incorporation of residue).

Some environmental side effects (both beneficial and detrimental) may be expected from the adoption of these techniques, i.e., reduction of wind and water erosion, control of soil temperature (Lal, 1986, Fortin and Pierce, 1990), reduction of bulk density (ICRI- SAT, 1986) coupled with better moisture retention (Papendick and Parr, 1989). Some phytotoxic or- ganic acids like acetic acid, butyric acids etc, may be produced in the decomposition of crop residue in

some anaerobic pockets of the soil (Harper and Lynch, 1981).

4. Conclusions

The following conclusions can be drawn from the study:

(1) In a rice-wheat cropping, rice required more energy (15.4GJ/ha) than wheat (10.8GJ/ha) for farm operation.

(2) Irrigation required the highest energy in all farm operation, i.e., 75% and 67% of total opera- tional energy for rice and wheat, respectively.

(3) Crop residue required the greatest input en-

A. Sarkar / Agriculture, Ecosystems and Environment 61 (1997) 59-67 67

ergy in residue treated plots more when the entire quantity of residue was added than only half the residue addition. Crop residue again required the largest input energy in residue plus fertilizer treated plots, more in full residue-fertilizer plots than in half-residue fertilizer plots.

(4) Application of half the crop residue with fertilizer produced consistently the highest grain yield of rice (averagely 5700Kg/ha) and wheat (aver- agely 4200 Kg/ha).

(5) Application of half the crop residue with fertilizer was the most economic user of fossil fuel producing 0.415Kg of rice and 0.442Kg of wheat grain/MJ of fossil fuel used.

(6) Labour productivity: Application of half the crop residue with fertilizer was also the most eco- nomic user of labour producing averagely 8.25 Kg of rice grain and 8.05 Kg of wheat grain/hour of labour.

(7) Thus the trade-offs studies showed that addi- tion of only the residue had little benefit, while applying only the fertilizer was moderate in this respect. But a combined application of half the residue with fertilizer proved the best, producing maximum output per unit use of fossil fuel and of labour. But one should not exceed this limit of residue incorporation with fertilizer otherwise there is reduction in such benefit in both the crops. So keeping in view the fast depleting fossil energy sources, incorporating half the residue production of the crop itself with the recommended fertilizer level in rice-wheat cropping may be a wise practice in solving the energy problem for higher production in this part of the sub-tropics. Future research should concentrate on the ways and means for better field decomposition of this organic matter (crop residue) leading to higher crop yield per unit use of fossil fuel and labour even with lesser quantity incorporation.

Acknowledgements

The financial support by the Indian Council of Agricultural Research, New Delhi through Project Directorate for Cropping Systems Research, Modipu- ram for the study is gratefully acknowledged.

References

Fortin, G.C. and Pierce, F.J., 1990, Developmental and growth effects of crop residues on cron. Agron. J. 82: 710-715.

Gotah, S. and Onikuru, Y., 1991. Organic acid in a flooded soil amended with rice straw and their effect on the growth of rice, Soil Sc. and Plant Nutrition, 17 (1): 1-8.

Harper, S.H. and Lynch, J.M., 1981. The kinetics of straw decom- position in relation to its potential to produce the phytotoxic acetic acid. J. Soil Sc. 32: 621-637.

Hwang, S.W., Ryu, I.S. and Park, J.K., 1989. The effect of application of rice straw and gypsum on the chemical proper- ties of the soil and rice growth in saline soil. Res. Rep. of Rural Dev. Adm. Soils and Fert., 31 (1): 37-50.

ICRISAT, 1986. International Crops Research Institute for the Semi-Arid Tropics. Annual Rep. 1985.

Lal, R., 1986. Soil Surface management in the tropics for inten- sive land use and high and sustained production. Adv. Soil Sc. 7, 1-105.

Mishustin, E.W., Vestrov, I.S., Delgikh, Yu. R., Rao, V.R. and Sidorenko, O.D., 1975. The use of rice straw as an organic manure for rice. Agrokhimiya, No. 7:80-87.

Mittal, V.K., Mittal, J.P. and Dhawan, K.C., 1985. Research digest on energy requirements in agricultural sector (1971-82). Coordinating Cell. All India Coordinated Research Project on Energy Requirement in Agricultural Sector, Punjab Agricul- tural University, Ludhiana, 259. pp.

Pal, M., Singh, M., Saxena, J.P. and Singh, H.K., 1985. Energet- ics of cropping systems. Indian J. Agron., 30 (2): i-Lxi.

Papendick, R.I. and Parr, J.F., 1989. The value of crop residue for water management systems for rainfed agriculture in the Su- dano Sahelian zone: Proceedings of an International Work- shop, 7-11 Jan 1987. ICRISAT Centre, India and Niger.

Singh, S., Mittal, J.P., Singh, M.P. and Bakhashi, R., 1990. Unit energy consumption for paddy-wheat rotation. Energy Con- vers. Mgmt., 30 (2):121-125.

Stott, D.F., Stroo, H.F., Elliett, L.P., Papendick, R.I. and Unger P.N., 1990. Wheat residue loss from fields under no till management Agron. J., 54 (1): 92-98.

Verma, U.N., Srivastava, V.C. and Prasad, R.S., 1989. Effect of Zero tillage on wheat (Triticum aestivum) with rice (Oryza sativa) stubble mulching. Indian J. Agric. Sc., 59 (10):669- 671.

Vlek, P.L.G. (1990). Thr Role of Fertilizers in sustaining agricul- ture in Sub-Sharan Africa. Fert. Res., 26: 327-339.

Will, B.R., Norman, R.J. and Helms, R.S. (1989). The effect of fertilization of wheat when wheat follows rice in rotation. Res. Series Arkansas Agril ExptL Stn., No. 385:35-37.

Wold, J.D., Rhotes, G.N. Jr., Groveel, J.G., Gosaver, B.M., Arvin, M.K., and Churck, R.L., 1989. Activity of imazaguin in soil solution as affected by incorporated wheat (Triticum aestivum) straw. Weed Science, 37 (2):254-258.