Productivity, Profitability and Quality of Soybean [Glycine max (L.) Merrill] Influenced by Phosphorus and Sulphur Fertilization

Soybean [Glycine max (L.) Merrill] is an important oilseed and food grain legume crop. It has paramount importance in human and animal nutrition, because it is a major source of edible vegetable oil and high protein feed as well as food in the world. It is highly nutritious containing higher amount of 22-24% protein, 1.3% fat and 60% carbohydrates on dry weight basis and it is rich source of calcium and iron. On the national basis, soybean occupied an area of 12.09 million ha with production and productivity of 11.22 metric tonnes and 928 kg ha^-1, respectively (Anonymous, 2020). Soybean is grown as a major oilseed crop mainly in south-eastern parts of Rajasthan during kharif season. It covers 1.12 million ha with an annual production and productivity of 0.52 metric tonnes and 469 kg ha^-1, respectively in the state (DAC and FW, 2019-20).

Emergence of multiple-nutrient deficiencies due to poor recycling of organic resources and unbalanced use of fertilizers are important factors to be considered for low productivity of soybean (Chaturvedi et al., 2010 and Jadon et al., 2019). It is an established fact that amongst nutrients, NPK and S are considered to be the most important for exploiting genetic potential of soybean crop.

Improved application technology of phosphorus fertilizer are required to optimize crop yields and reduce the environmental impacts of phosphorus. The soybean yield attributes were significantly influenced by the phosphorus fertilizer source in addition to zinc. Its uptake and utilization by soybean are essential for ensuring proper nodule formation and improving yield and quality of the crop. Phosphorus fertilizer sources have been shown to positively influence on soybean yields (Gonyane and Sebetha, 2022).

Sulphur is essential for synthesis of proteins, vitamins and sulphur containing essential amino acids and is also associated with nitrogen metabolism. The good yield of soybean can be achieved by balanced and adequate supply of phosphate, sulphur and other deficient, nutrients (Suman et al., 2018). Sulphur is used as soil amendment for amelioration, as plant nutrient for increasing yield and quality of crop produce. Still the studies on effect of sulphur in soybean are very meagre. The sulphur is required in high amount by the oilseeds and hence has been identified as key nutrient responsible for high production. The present investigation was therefore initiated to work out the response of phosphorous and sulphur levels on productivity, yield and quality of soybean

The experiment conducted during kharif 2021 at Instructional Farm, College of Agriculture, Ummedganj, Kota (Rajasthan), which is situated at Humid South Eastern Plains of Rajasthan. This zone possesses typical sub-tropical conditions with maximum and minimum temperatures ranged between 30.2°C to 42.3°C and 20.3°C to 23.0°C during kharif, 2021. The total rainfall received during crop season was 1229 mm. The soil of experimental site was clay loam in texture, slightly saline in reaction. Soil was medium in available nitrogen (264 kg ha^-1) and phosphorus (21.7 kg ha^-1) while high in potassium (388 kg ha^-1) and sufficient in DTPA extractable micronutrients with pH (7.61) and EC (0.52 dS m^-1). Recommended dose of fertilizer 20:40:40:30 (NPKS kg ha^-1) along with Rhizobium japonicum culture seed inoculation. Among these nitrogen and potassium was applied as basal dose through urea and muriate of potash, whereas phosphorus and sulphur were applied through TSP and elemental sulphur according to treatments as basal dose.

An experiment was laid out in factorial randomized block design with three replications The twelve treatments combinations was comprised four levels of phosphorus viz., 0, 20, 40 and 60 kg ha^-1 and three levels of sulphur viz., 15, 30 and 45 kg ha^-1. Data on yield parameters like number of pods per plant, seed per pod, seed index, straw yield, biological yield and grain yield were recorded as per standard procedures. Plant samples (grain and straw) were collected after harvesting from each plot. Protein content in seed was obtained by multiplying the per cent nitrogen content by 6.25 (Simson et al., 1965). Oil content  in soybean seed was determined by Soxhlet’s Ether Extraction method (AOAC, 1965). The data were statistically analysed by adopting appropriate method of standard analysis of variance (Gomez and Gomez, 1984). 

Effect of phosphorus application
 
Yield attributes and yield
 
Data regarding to the yield attributes and yields of soybean was significantly increased with increasing levels of phosphorus up to 60 kg ha^-1 (Table 1).



The maximum pods (45.72 plant^-1) were recorded with the application of 60 kg P₂O₅ ha^-1 in soybean over 20 kg P₂O₅ ha^-1 (36.06 plant^-1) and control (32.00 plant^-1). However, it was found at par with 40 kg P₂O₅ ha^-1 (43.33 plant^-1). Application of 60 kg P₂O₅ ha^-1 gave significantly higher number of seeds (2.52 pod^-1) which was found at par with 40 kg P₂O₅ ha^-1 (2.39 pod^-1). Application of 60 and 40 kg P₂O₅ ha^-1 were found at par in respect of test weight (128.56 and 126.26 g) of soybean. However, it was found significantly superior over 20 kg P₂O₅ ha^-1 and control, respectively. The application of 60 kg P₂O₅ ha^-1 produced maximum seed yield (1942 kg ha^-1) which was statistically superior over 20 kg P₂O₅ ha^-1 and control (1566 and 1462 kg ha^-1), respectively. The seed yield (1839 kg ha^-1) remained at par with 40 kg P₂O₅ ha^-1 of soybean. The highest straw yield (3305 kg ha^-1) was observed under application of 60 kg P₂O₅ ha^-1 which was remained at par with 40 kg P₂O₅ ha^-1 (3137 kg ha^-1), but it was found significantly superior over 20 kg P₂O₅ ha^-1 and control, respectively. Application of 60 kg P₂O₅ ha^-1 gave maximum biological yield (5247 kg ha^-1) over 20 kg P₂O₅ ha^-1 and control. However, it was found at par with 40 kg P₂O₅ ha^-1 (4976 kg ha^-1) biological yield of soybean.

Phosphorous application accelerated the production of photosynthates and their translocation from source to sink, which ultimately gave the higher values of yield contributing characters. Increase in yield contributing characters has also been reported by Meena et al., (2006) and Kumar et al., (2007). This was mainly due to fact that the better availability of nitrogen and phosphorus caused well developed root system having higher nitrogen fixing capacity resulting better growth and development of plants and better diversion of photosynthates towards sink to source (Singh et al., 2017).
 
Quality parameters
 
A reference to data presented in Table 2 revealed that the maximum protein content (41.41 per cent) in soybean seed was recorded with application of 60 kg P₂O₅ ha^-1 over 20 kg P₂O₅ ha^-1 and control. However, it was found at par with 40 kg P₂O₅ ha^-1 (41.18 per cent) protein content. The application of 40 and 60 kg P₂O₅ ha^-1 was found at par with each other in terms of protein yield (807 and 760 kg ha^-1) over 20 kg P₂O₅ ha^-1 and control. The highest oil content (20.53 per cent) was recorded with application of 60 kg P₂O₅ ha^-1. It registered remarkable increase in oil content in soybean seed to the tune of 3.47 and 4.53 per cent higher over 20 kg P₂O₅ ha^-1 and control. However, it was found at par with 40 kg P₂O₅ ha^-1 (20.32 per cent) oil content. Significantly highest oil yield (400 kg ha^-1) was recorded with application of 60 kg P₂O₅ ha^-1 over 20 kg P₂O₅ ha^-1 and control. However, it was found at par with 40 kg P₂O₅ ha^-1 (375 kg ha^-1) soybean oil yield.

The increase in oil content with phosphorus application could be due to the fact that phosphorus helped in synthesis of fatty acids and their esterification by accelerating biochemical reactions in glyoxalate cycle (Dwivedi and Bapat, 1998). The maximum protein and oil content were recorded with a treatment combination of 80 kg P₂O₅ and 40 kg sulphur ha^-1. Similar findings were also observed on soybean by Jahangir et al., (2009).


 
Economics
 
It is obvious from the data presented in Table 2 that the application of 60 kg P₂O₅ ha^-1 provided the highest net returns (₹ 48497 ha^-1). It registered remarkable increase in net returns to the tune of 46.2 and 66.73 per cent higher over 20 kg P₂O₅ ha^-1 and control, respectively. However, it was found at par with 40 kg P2O5 ha-1 (` 44575 ha-1). Significantly highest B: C ratio (1.39) fetched under application of 60 kg P₂O₅ ha^-1. It registered remarkable increase in B:C ratio to the tune of 43.2 and 53.0 per cent higher over 20 kg P₂O₅ h^a-1 and control, respectively. However, it was found at par with 40 kg P₂O₅ ha^-1 (1.29).

Application of 60 kg P₂O₅ ha^-1 showed mark improvement in seed yield and thus gaining more profit in terms of net returns and benefit: cost ratio. The findings are in agreement with that of similarly, the monetary gains in terms of gross return and net return increased consistently and significantly with varying levels of phosphorus (Dhage et al., 2014). The computation of cost of cultivation is important because it decides the option for the farmers to choose the production practices, according to their investment capacity. Similar findings were also reported by Munda et al., (2018) and Raghuveer et al., (2017). 

Effect of sulphur application
 
Yield attributes and yield
 
Data pertaining to various yield attributes and yields were presented in Table 1. Aapplication of 45 kg sulphur ha^-1 produced the maximum pods (42.60 plant^-1) which was higher of 22.8 per cent over 15 kg sulphur ha^-1. However, it was found at par with 30 kg sulphur ha^-1 (40.54 plant^-1) pods of soybean. Significantly higher number of seeds pod^-1 (2.45) was recorded under application of 45 kg sulphur ha^-1 which was found at par with 30 kg sulphur ha^-1 (2.33 seeds pod^-1) over application of 15 kg sulphur ha^-1. The application of 45 kg sulphur ha^-1 gave significantly higher test weight (128.43 g) by 8.4 per cent over 15 kg sulphur ha^-1. However, it was found at par with 30 kg sulphur ha^-1 (126.11 g) test weight of soybean. Application of 45 kg sulphur ha^-1 gave significantly higher seed yield (1870 kg ha^-1) over 15 kg sulphur ha^-1. The seed yield (1773 kg ha^-1) remained at par with 30 kg sulphur ha^-1. Application of 45 kg sulphur ha^-1 attained the maximum straw yield of soybean (3179 kg ha^-1) and remained at par with 30 kg sulphur ha^-1 (3028 kg ha^-1) over 15 kg sulphur ha^-1. Application of 45 kg sulphur ha^-1 gave significantly higher biological yield (5048 kg ha^-1) over 15 kg sulphur ha^-1 (3971 kg ha^-1). However, it was found at par with 30 kg sulphur ha^-1 (4800 kg ha^-1) biological yield of soybean.

The yield increased under sulphur fertilization might be ascribed to increased pods plant^-1 and seeds pod^-1 with heavier seeds. Thus, significant improvement in yield obtained under sulphur fertilization seems to have resulted owing to increased concentration of sulphur in various parts of plant that helped maintain the critical balance of other essential nutrients in the plant and resulted in enhanced metabolic processes. Vyas et al., (2006) also noticed increased yield of soybean with application of sulphur. Sulphur plays a vital role in improving vegetative structure for nutrient absorption, strong sink strength through development of reproductive structures and production of assimilates to fill economically important sink (Sharma and Singh, 2005).
 
Quality parameters
 
A perusal of data presented in Table 2 showed that the maximum protein content was recorded under application of 45 kg sulphur ha^-1 (40.70 per cent), which was found at par with 30 kg sulphur ha^-1 (40.55 per cent) over 15 kg sulphur ha^-1 (37.16 per cent) in soybean seed. Significantly higher protein yield (764 kg ha^-1) was recorded with application of 45 kg sulphur ha^-1, which was found at par with 30 kg sulphur ha^-1 (723 kg ha^-1) over 15 kg sulphur ha^-1 (547 kg ha^-1). The maximum oil content (20.53 per cent) was recorded with application of 45 kg sulphur ha^-1 which was found at par with 30 kg sulphur ha^-1 (20.15 per cent). The extent of increase in oil content in soybean seed due to application of 45 kg sulphur ha^-1 was 4.8 per cent higher than application of 15 kg sulphur ha^-1. Significantly highest oil yield (384 kg ha^-1) was recorded with application of 45 kg sulphur ha^-1 over 30 and 15 kg sulphur ha^-1 (358 and 287 kg ha^-1) in soybean seed.

It might be due to involvement of sulphur in the synthesis of fatty acids and also increases protein quality through the synthesis of certain amino acids such as cysteine, cystine and methionine. The results supported to the earlier findings of (Pable and Patil, 2011) and (Devi et al., 2012) in soybean. Increase in oil content due to sulphur application can be attributed to the key role played by sulphur in biosynthesis of oil in oilseed plants. The increase in protein content may be accounted for the increase in synthesis of sulphur containing amino acids. Such beneficial effects of sulphur fertilization were also reported by Nath et al., (2018).
 
Economics
       
A critical examination of data presented in Table 2 showed that the maximum net returns (₹ 44193 ha^-1) were recorded under application of 45 kg sulphur ha^-1 which was closely followed by 30 kg sulphur ha^-1 (₹ 41868 ha^-1). The extent of increase net returns due to application of 45 kg sulphur ha^-1 was 45.2 per cent higher over 15 kg sulphur ha^-1. Significantly highest B:C ratio (1.23) was recorded under application of 45 kg sulphur ha^-1, which was closely followed by 30 kg sulphur ha^-1 (1.22). The extent of increase in B:C ratio due to application of 45 kg sulphur ha^-1 was 30.8 per cent higher over 15 kg sulphur ha^-1.

The determination of economics is the most important to evaluate the effect of treatments from farmers as well as planners’ point of view. Application of 45 kg sulphur ha^-1 showed mark improvement in seed yield and thus gaining more profit in terms of net returns and B:C ratio over application of 15 kg sulphur ha^-1. The findings are in agreement with the sulphur application is highly profitable as shown by value cost ratio in soybean under field condition (Tandon et al., 2007).

It is concluded that the application of 40 kg phosphorus ha^-1 and 30 kg sulphur ha^-1 is profitable dose for obtaining higher seed yield of soybean, net returns and B: C ratio in the experiment. The quality parameters of soybean also showed considerable increment due to application of 40 kg phosphorus ha^-1 and 30 kg sulphur ha^-1. Hence this dose of phosphorus and sulphur is proved as productive and beneficial. These levels of phosphorus and sulphur fertilizer may be passed on to the farmers for obtaining higher returns in the clay loam soils of zone Vth of Rajasthan.

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