Economics of Residues Incorporation and Phosphorus Application for Direct Seeded Rice and Wheat under Saline Soil

Two-year long field study was conducted using a permanent layout to investigate the economics of crop residues incorporation (2 t∙ha−1) and P application (0, 40, 80 and 120 kg P2O5 ha−1) to directly sowing of rice and wheat crops gown under naturally salt-affected calcareous soil (ECe = 4.59 dS m−1; pHs = 8.38; SAR = 6.57 (mmolc L−1)1/2; CaCO3 = 3.21%; Extractable P = 4.07 mg∙kg−1; sandy clay loam) at farmers field in district Hafizabad during the year 2012-13. Split plot design (crop residues in main plots and P application in sub plots) was followed with three replications. Agronomic data on growth and yield were collected at the time of each crop maturity. Maximum growth and yield of both the crops were harvested from the plots where P2O5 was applied @ 80 kg∙ha−1 along with crop residues incorporation. On an average of two years, maximum paddy (3.26 t∙ha−1) and wheat grain (3.56 t∙ha−1) yield were produced with P application @ 80 kg P2O5 ha−1 along with crop residues incorporation. Although, the yield harvested with this treatment (80 kg P2O5 ha−1 + crop residues) performed statistically equal to 120 kg P2O5 ha−1 without crop residues incorporation during both the years, however, on an average of two years, grain yield of directly sowing rice and subsequent wheat was significantly superior (22% and 24% respectively) than that of higher P rate (120 kg∙ha−1) without crop residues. Overall, continuous two-year crop residues incorporation further increased (17%) paddy yields during the follow up year of crop harvest. Economic analyses of both the crops were carried out to choose the best treatment with adequate economic benefits as compared to those without crop residue incorporation. Maximum net benefit of Rs = Corresponding author. I. A. Mahmood et al. 935 108,680/for direct seeded rice and Rs = 99,362/for wheat grown with 80 kg P2O5 ha−1 application under crop residues incorporation was determined. Among P application treatments without crop residues incorporation, the maximum net benefit (Rs = 75,874/and Rs = 65,725/-) and highest residual values (49,809 and 39,160) for direct seeded rice and wheat respectively, were obtained with extended P application rate (120 kg P2O5 ha−1) which was not again as much as that of 80 kg P2O5 ha−1 application with crop residues incorporation.


Introduction
With world population now more than seven billion is a timely moment for such an assessment to boost up the grain production for fulfilling the mounting demands.Population growth and economic burden are exerting the pressure on arable lands.Intensive cropping are exhausting nutrients from soil equilibrium gradually which is among the major constraints to get optimum yields.The specter of possible changes in traditional agriculture could be a step forward to release these pressures.It is the time to consider how we can move "towards sustainability" towards a vision of natural resources management that supports current population's demands otherwise leaving the future generations on an equitable soil degradation owing to gradual nutrient depletion.Soil is critical component of the resource base upon which a successful agriculture depends.To move towards sustainability, agriculture and natural resource management interests must recognize that they are equal partners in the effort.The challenges are to adapt and extend our knowledge about soil health to develop economically productive, culturally appropriate and environmentally sound systems.A flexible ongoing process is necessary to set research priorities to support inherently dynamic agricultural techniques.
In Pakistani, totals extents off salt-affected areas is 6.3 mha, of which 1.89 mha is saline, 1.89 mha is permeable saline-sodic, 1.02 mha is impermeable saline-sodic while sodic-soils is only 0.028 mha.Provinces wised distributions off saline's patches outs of 1.89 mha, 0.94 mha is in the Punjab, 0.5 mha in Sindh and 0.45 mha is in Khyber Pakhtun Khawa [1].Soil salinity and P fixation reduce activity of soil microorganisms.Nutrient mining due to intensive cropping and practice of imbalance fertilizers applications is the main examples of soil resources degradation.A significant reduction in the yield of rice and wheat owing to these reasons is 68% and 64%, respectively, causing a loss estimate from 0.3 to 1.0 billion dollar per annum [2].The interrelated apprehensions of rising population definitely impose economic pressures; intensified land use and environmental degradation at local and regional levels are serious issues to concern.Combinations of biological and societal resources are required to make successful agricultural production managements and its sustainability will necessitate the changes in philosophy and operating procedures for improving productivity.A major limitation in the rice-wheat cropping system is the short time between rice harvesting and wheat cultivation and any delay in planting adversely affects crop yields.As the result of improved farm machinery convenience, a large area under rice and wheat crops are being harvested with combined harvester which leaves behind a massive loose straw whose removal or exploitation in a short time period is not so easy.Rice is grown on 2.58 mha with annual straw production of about 4 million tons [3].The situation compels farmers to burn them for preparation their lands for timely sowing of subsequent crops [4] [5].Circumstances after the harvest of wheat crop are also the same.Crop residues are rich source of plant nutrients that farmers demolish through burning which not only causes nutrient losses but also pollutes the environment.In addition to these restrictions, P fixation in our soils due to calcareousness and high pH are other constraints considerably reducing crop yields and under saline conditions, its availability is further declined.The growing crop plants under such environment demand relatively higher nutrition to reach the potential yields.Since the prices of P fertilizers are becoming out of the reach of resource poor farmers day by day as a result they don't be anxious about nourishing their growing crop plants with balanced fertilization [6].The left over residues could be recycled if its burning is discouraged.Generally, a large portion of nutrients taken up by the plants remains in the straw which can be utilized for the growth of subsequent crops through their incorporation [7].In many studies, recycling of crop residues is reported to increase the nutrient status of the soils and hence crop productivity [8]- [10].
Traditionally transplanting of rice is a very hard and difficult process of cultivation which requires expensive labour and extensive machinery tools for puddling as well.Consequently, directly sowing of rice is an option which saves all these expenses and complexities.Keeping all these points in view, two year field study using a permanent layout was conducted under naturally saline soil to investigate the economics of crop residue incorporation as well as P application and their impact on direct seeded rice paddy and wheat grain yields.
Recommended basal dose of N @ 100 kg•ha −1 (half at sowing time and remaining half at tillering stage) and K @ 50 kg•ha −1 as SOP were applied to all the plots at the time of sowing.Soaked seed (for 24 h) of rice cv.Supper-2000 @ 40 kg•ha −1 was broad-casted uniformly.The same inputs were applied to intermediate wheat crop.Effective weedicides were used to control weeds and the crop was grown to upto maturity.All agronomic requirements and plant protection measures were met throughout the growth period whenever required.At maturity, each crop was harvested and direct seeded rice paddy and wheat grain yields were recorded.
The economic analysis of crop residues incorporation and four P application rates to direct seeded rice and wheat crops was computed by using the method as described earlier [11].

Growth and Yield of Direct Seeded Rice and Wheat Crops
On an average of two years data, maximum paddy (3.26 t•ha −1 ) and wheat grain (3.56 t•ha −1 ) yields were produced with P application @ 80 kg P 2 O 5 ha −1 alongwith crop residues incorporation (Table 1) which was comparable with higher P rate (120 kg•ha −1 ) under no crop residues incorporation.The paddy and wheat grain yields produced by this treatment showed 22% and 24%, respectively additional yield over control (0 kg P ha −1 + crop residues).Under crop residues incorporation, further increase in P application (120 kg P 2 O 5 ha −1 ) caused 6% paddy yield reduction as compared to the P application @ 80 kg P 2 O 5 ha −1 .Crop residue incorporation positively contributed in grain yield of direct seeded rice and subsequent wheat particularly during second year.This was most probably due to complete decomposition and mineralization of added crop residues that enriched the soil with mineral nutrients in addition to improvement in soil physical condition by ameliorating toxic effects of saline ions.Moreover, water and P retention capacity might have also been improved due to added crop residues that retained comparatively excess moisture and P availability for a longer time.Besides, production of acid farming substances by microbial activities and partial pressure of CO 2 released during crop residues decomposition decreased soil pH and enhanced P availability and other necessary plant nutrients which encouraged healthy plant growth and hence yields.Similar points of view have also been documented by [12] [13].Further, adequate P fertilization promoted vigorous plant growth that ultimately improved number of grains per panicle resulting in increased yields of direct seeded rice and succeeding wheat crop [14] [15].The increase in yield due to crop residues incorporation as well as P application has also been well documented by [16]- [20].

Partial/Budget Analysis of Direct Seeded Rice and Wheat Crops
Partial budget analysis for P application rates (Table 2 and Table 3) showed that all P application rates under crop residues incorporation gave higher benefit than that of without crop residues incorporation.However maximum net benefit for direct seeded rice and wheat crops was calculated from P application @ 80 kg P 2 O 5 ha −1 with crop residues incorporation under saline soil.This treatment for direct seeded rice and wheat again performed to be superior than that of elevated P application rate (120 kg P 2 O 5 ha −1 ) without crop residues incorporation.Whereas, minimum net benefit was obtained from the plots receiving 40 kg P 2 O 5 ha −1 without crop residues incorporation.Correspondingly, P application @ 80 kg P 2 O 5 ha −1 with crop residues incorporation also demonstrated the highest Cost Benefit Ratio (CBR) for direct seeded rice and wheat.

Cost Benefit Ratio (CBR), Net Benefit (NB) and Marginal Rate of Return (MRR)
The data in Table 4 and Table 5 indicates that maximum CBR (4.9) for direct seeded rice was calculated with 80 kg P 2 O 5 ha −1 under crop residues incorporation and it was 4.8 with higher rate of P 2 O 5 (120 kg•ha −1 without crop residues incorporation).Similarly, the highest CBR of 4.5 for wheat was calculated with 80 kg P 2 O 5 ha −1 under crop residues incorporation and it was 4.4 with higher rate of P 2 O 5 (120 kg•ha −1 without crop residues incorporation).Generally, all P application rates along with crop residues incorporation showed much higher NB and highest residual value being the maximum NB with 80 kg P 2 O 5 ha −1 application to direct seeded rice (Rs = 108,680/-) and wheat (Rs = 99,362/-) crops.Among P application treatments without crop residues incorporation, the maximum NB (Rs = 98,990/-and Rs = 90,125/-) and highest residual values (72,925 and 63,560) for direct seeded rice and wheat respectively, were obtained with higher P application rate (120 kg P 2 O 5 ha −1 ) which were not again as much as that of 80 kg P 2 O 5 ha −1 application with crop residues incorporation.Similarly Table 6 showed that highest MRR (4063) for direct seeded rice was computed with 40 kg P 2 O 5 ha −1 under crop residues incorporation and while it was 3950 with 80 kg P 2 O 5 ha −1 without crop residues incorporation).Whereas Table 7 indicated, the highest MRR (3114) for wheat was calculated with 40 kg P 2 O 5 ha −1 under crop residues incorporation and it was (4179) with 80 kg P 2 O 5 ha −1 without crop residues incorporation).
On the basis of this investigation, it is concluded that crop residues incorporation is the best choice rather it's   burning to improve direct seeded rice and wheat yields with 80 kg P 2 O 5 ha −1 application under slightly saline soil.

Residual Analysis for Direct Seeded Rice and Wheat Crops
Residual analysis is done to verify the results of marginal analysis.The results of residual analysis (Table 8 and Table 9) demonstrate that the highest residual values of direct seeded rice and wheat were observed with (80 kg P 2 O 5 ha −1 and crop residues incorporation) followed by 120 kg P 2 O 5 ha −1 without crop residues incorporation.The improvement in their economics is definitely attributed to continuous P application and crop residues incorporation that might have altered the soil physical conditions due to which P availability and its utilization was enhanced.Consequently, the nutrient utilization efficiency positively happened to be a factor for healthy growth and yield of direct seeded rice and wheat crops under adverse soil condition.This could be supported by the findings of [20]- [24], who had documented similar points of view regarding better correlation between nutrients and plant growth under improved soil physical conditions.The similar trend in economic analysis results of mungbean cultivars and P application rates have been reported by [25].Performance of green gram and response functions as influenced by different levels of nitrogen and phosphorous was computed by [26].Similarly the results of [27] showed that application of inorganic fertilizers and organic manures enhanced nutrients availability and improved economical production of mungbean.On the basis of all economic analyses of research work data   (2011-2012), the incorporation of crop residues and 80 kg P 2 O 5 ha −1 could be recommended to farmers to get maximum return by growing direct seeded rice and wheat on marginally salt-affected soils.The findings could also be supported by the results of [28].

Conclusion
Our results indicated that P application @ 80 kg P 2 O 5 ha −1 along with crop residues incorporation (2 ton•ha −1 ) was found to be superior to rest of the treatments in term of producing maximum grain yield of both direct seeded rice and wheat crop grown under marginally saline soil.

Table 2 .
Partial budget analysis for direct seeded rice grown with and without CR under saline soil.

Table 3 .
Partial budget analysis for wheat grown with and without CR under saline soil.

Table 4 .
Cost Benefit Ratio (CBR) for direct seeded rice grown under saline soil.

Table 5 .
Cost Benefit Ratio (CBR) for wheat grown under saline soil.

Table 6 .
Marginal Rate of Return (MRR) for direct seeded rice grown under saline soil.

Table 7 .
Marginal Rate of Return (MRR) for wheat grown under saline soil.Total Cost that Vary; MC = Marginal Cost; NB = Net Benefit; MNB = Marginal Net Benefit; MRR = Marginal Rate of Return; +CR = With Crop Residue; −CR = Without Crop Residue.

Table 8 .
Analysis using Residual for direct seeded rice grown under saline soil.

Table 9 .
Analysis using Residual for wheat grown under saline soil.Total Cost that Vary; NB = Net Benefit; +CR = With Crop Residue; −CR = Without Crop Residue.