Effect of Phosphorus and Sulphur on Yield and Economics of Summer Greengram ( Vigna radiata )

A field experiment was conducted at Krishi Vigyan Kendra

Pulses are the major source of dietary protein in the vegetarian diet of our country. Besides being the source of protein, they maintain soil fertility through biological nitrogen fixation and thus play a vital role in furthering sustainable agriculture (Kannaiyan, 1999). Pulses are also an important component of cropping systems in marginal and sub -marginal areas of dry land farms as 92 per cent of the pulse production in India is realized from dry lands or the areas depending on rains. India is the largest producer of pulses in the world, the per capita consumption over the years has come down from 61 g day-1 in 1951 to 30 g day-1 in 2008 (Reddy, 2009). In India, pulses are grown in nearly 23.28 million hectare area with production status of nearly 14.66 million tonnes at an average productivity level of 630 kg ha-1 (Economic Survey, 2010-11). Green gram is the third most important pulse crop after chickpea and pigeon pea. At the national level it is grown on 3.10 m ha area and produces nearly 0.94 m t with an average productivity of 304 kg ha-1 (Govt. of India, 2010). In Rajasthan, greengram is cultivated on 1.06 m ha land mass with 0.41 m t production at a yield status of 390 kg ha-1 (Govt. of Rajasthan, 2010).
Greengram is generally grown as a rainfed crop during rainy season in Rajasthan either as sole crop or mixed crop with cereals. However, with the enhanced irrigation facility in southern Rajasthan, the cropping intensity has increased to quite an extent. In the canal command areas, this crop is *Corresponding author email: rb_agro@rediffmail.com now raised in summer season in between two main seasons i.e. winter and rainy. This has opened avenues of intensifying crop production in the tribal dominated belt. Perhaps, because of these distinct features and higher economic returns, farmers have shown renewed interest towards this pulse crop (Chadha, 2010).

Materials and Methods
A field experiment was conducted during summer 2010 and 2011 at Krishi Vigyan Kendra, Dungarpur. The soils were sandy clay loam in texture and alkaline in reaction (pH 8.1 and 7.9), low in organic carbon (0.48 g kg-1 soil), available nitrogen (247 kg ha-1), medium in available phosphorus (17.9 kg ha-1), high in available potassium (282 kg ha-1) and low in available sulphur (8.8 ppm). The treatments comprised four levels of phosphorus (0, 20, 40 and 60 kg P2O5 ha -1 ) and four levels of sulphur (0, 15, 30 and 45 kg S ha-1) thereby, making sixteen treatment combinations and were replicated four times in factorial randomized block design. The crop was sown in the same field on March 18, 2010 and March 15, 2011. As per the treatment combinations, phosphorus and sulphur were applied manually through DAP and mineral gypsum at the time of sowing in furrow at 5 cm below the seeding depth, respectively. A recommended dose of 25 kg nitrogen ha-1 was ensured through urea in each treatment. The seed of greengram variety SML-668 was treated with bavistin at 2 g kg-1. It was followed by bacterial culture (Rhizobium phseoli and PSB) treatment. Furrows were opened manually at 25 cm apart and seeds were placed at a depth of 3 to 4 cm, using seed rate 15 kg ha-1 .Weed control, irrigation and plant protection measure were followed as per zonal package. The observations were recorded for the traits viz., grain yield (kg ha-1) and stover yield (kg ha-1). The net return (Rs. ha-1) was calculated by deducting the cost of cultivation from gross realization for each treatment. The benefit cost ratio (B C ratio) was calculated by gross returns (Rs. ha-1) divided by cost of cultivation (Rs. ha-1). The data were subjected to statistical analysis by adopting appropriate method of analysis of variance as described by Cocharan and Cox (1967). Assuming homogenicity in data over two years of experimentation, pooled analysis was also carried out as per Gomez and Gomez (1984).

Effect of phosphorus
Application of phosphorus upto 60 kg P2O5 ha -1 resulted in significantly higher grain and stover yield of summer greengram. On pooled basis, application of phosphorus at 60 kg P2O5 ha -1 was responsible for producing 14.39 and 14.08 per cent higher grain and stover yield over control (648 and 1091 kg ha-1), respectively (Table 1). It is an established fact that photosynthesis together with availability of assimilates (source) and storage organs (sink) exert an important regulative function on the complex process of yield formation. The regulatory functions of phosphorus in photosynthesis and carbohydrate metabolism of leaves can be considered to be one of the major factors limiting plant growth particularly during reproductive phase. The level of phosphorus during this period regulates starch/sucrose ratio in the source leaves and reproductive organs (Giaquinta and Quebedeaux, 1980). In many legumes (greengram being not exception to it) poor sink capacity is attributed to low retention of flower to form pods. Three possible explanation have been postulated, first being traditional favorite hormones, the second assumes that other organs compete with flower for want of metabolites, nutrients and last being modification of seconds refer to limitation of vascular system for rapid supply of growth inputs (metabolites and nutrients) from source of sink (Jeswani, 1986). Improvement in yield of summer greengram due to P fertilization was also observed by Bhuiyan et al. (2008) and Ali et al. (2010). Significantly greater net returns and B:C ratio were obtained with the application of 60 kg P2O 5 ha -1 except during second year which was on par with 40 kg P2O5 ha -1 in respect to net return. On pooled basis significantly higher net returns (Rs.16370.03 ha-1) and B:C ratio (2.13) were registered by applying 60 kg P2O 5 ha -1 but on par with 40 kg P2O5 ha -1 in respect to B:C ratio.

Effect of sulphur
Progressive application of sulphur upto 45 kg ha-1 significantly increased the grain and stover yield of summer greengram by 14.41 and 13.07 per cent over control (649 and 1084 kg ha-1), respectively (Table 1). Wareing and Patrick (1975) reported that improvement in yield was attributed to diversion of greater proportion of assimilates to the developing pods of groundnut due to increased sink strength reflected through its larger demand for photosynthesis. Finding of Kaisher et al. (2010) and Patel et al. (2010) are provided support to the findings of the present investigation Across the years of study and on pooled basis, an application of 45 kg S ha-1 resulted in significantly higher net returns and B:C ratio but on par with 30 kg S ha-1 in case of B:C ratio during first year of investigation. Pooled data (Table 1) indicate that application of 45 kg S ha-1 registered 24.34 and 10.66 per cent increase in net returns and B:C ratio over control, respectively.

Interaction effect
Though the effect of phosphorus and sulphur was significant individually the interaction effect was not significant with respect to grain and stover yield.

Net returns:
The interaction effect between the two nutrient elements under study positive trend on pooled basis in respect to net returns. At each level of phosphorus, application of sulphur showed variable response. While at 20 and 60 kg P2O5 ha -1 , application of S to the tune of 45 kg ha-1 gave higher net returns. However, under the influence of no phosphorus and 40 kg P2O5 ha -1 , not return increased by the appreciation sulphur upto 30 kg ha-1. Also variability in significance of phosphorus under different S levels was evident. Under no sulphur application, response of phosphorus was higher only upto 40 kg ha -1 of P2O5 .While the response was higher upto 60 kg P2 O5 ha -1 when sulphur was applied at the rate of 15 to 45 kg ha-1. The highest net returns (Rs.18869 ha-1) were registered by conjoint application of 60 kg P2O5 ha -1 and 45 kg S ha-1 which was higher over rest of the treatment combinations (Table 2).  (Table 3) showed that the interaction was seen on pooled basis with respect to B C ratio of summer greengram. Pooled analysis show that combined application of 60 kg P2O5 ha -1 and 45 kg S ha -1 proved to be best economic treatment (2.29) showing 19.27 per cent higher in  92). It was concluded that application of phosphorus at 60 kg P2O5 ha -1 and sulphur at 45 kg S ha-1 alone resulted in significantly higher grain and stover yield of summer greengram. While combined application of 60 kg P2O5 ha -1 and sulphur at 45 kg S ha -1 gave higher net returns and B:C ratio. There is improvement in yield 525 and economics of greengram over the existing general recommended dose of phosphorus.