Effect of phosphorus and sulphur application on their dynamics and nodulation in soil under black gram [Vigna mungo (L.) Hepper] crop

Pulses are included in cropping systems to improve soil health and its fertility status. The productivity of pulses mainly depends on proper management of nutrients particularly phosphorus and sulphur. Low organic matter content in light textured soils coupled with low and imbalanced application of nutrients to crop limits the full potential of yield and is the main barrier in the production of crops (Ghosh et al., 2003). Pulses are commonly grown in soils with low fertility status or with the application of small amount of organic and inorganic sources of plant nutrients, which in turn resulted in deterioration of soil health and crop productivity (Kumpawat, 2010).
 
Black gram [Vigna mungo (L.) Hepper] is one of the important pulse crops grown throughout the country. In northern parts of the country, it is commonly grown in summer and rainy season. It is a protein rich (25%) food, containing protein almost three times that of cereals. It supplies protein requirement of vegetarian population. Black gram accounts for 10% of the total pulse production in India. In Jammu and Kashmir, the total area under pulses is 28.7 thousand ha with an average productivity of 584 kg ha^-1, which is well below the national level productivity of 905 kg ha^-1 (Anonymous, 2016). One of the important factors responsible for its low yield is no or inadequate use of plant nutrients particularly phosphorus and sulphur.
 
Proper fertilization is essential to improve the productivity of black gram. It can meet its nitrogen requirement by symbiotic fixation of atmospheric nitrogen. The nutrients, which need attention, are phosphorus and sulphur (Thakur and Negi, 1985; Nandal et al., 1987). Black gram being a pulse crop requires high amount of phosphorus, which is among the essential macronutrients required for plant growth and development. It plays a key role in photosynthesis, metabolism of sugars, energy storage and transfer, cell division, cell enlargement, transfer of genetic information, root growth, nodulation and nitrogen fixation in plants. It serves as energy currency within plants and helps in root development and grain formation. Increase in yield brought by phosphorus application is significant and economically viable owing to its wide spread deficiency in soils of India in general and in soils of Jammu and Kashmir particularly. Motsara (2002) reported that 42, 38 and 20% samples of Indian soil were low, medium and high in available phosphorus, respectively. Accordingly, 80% of the soils in India need phosphorus application at recommended rate, whereas, the application of some quantity of phosphorus fertilizers would be essential to arrest phosphorus mining from the soil so as to sustain higher yield of crops. Similarly, most of the soils of Jammu region were tested low to medium in available phosphorus, except some patches and thus, they require phosphorus fertilization for optimum crop production.

Black gram also responds well to sulphur fertilization in sulphur deficient soils. Sulphur has a profound influence on protein synthesis by the pulses and is a part of cystein, cystine and methionine amino acid. Wide spread sulphur deficiency has been observed on larger areas due to the use of high analysis sulphur free fertilizers like urea and diammonium phosphate (DAP) in high yielding varieties and intensive cropping, and is more conspicuous in light textured soils low in organic matter (Sinha et al., 1995). Kour et al., (2010) reported that available sulphur in soils of Jammu region ranges between 2.42 to 5.1 mg kg^-1, which is below the critical limit.
 
In fact, sulphur is the second most important plant nutrient after phosphorus for pulses. A significant response of black gram to the application of phosphorus and sulphur has been reported earlier. Both phosphorus and sulphur can improve the quality and quantity of the crop. Sulphur interacts with phosphorus as phosphate ion is more strongly bound with clay complexes than sulphate (Hegde and Murthy, 2005). Phosphorus fertilizer application results in increased anion adsorption by phosphate, which releases sulphate ions in the soil solution (Tiwari and Gupta, 2006). Thus, it may be subjected to leaching if it is not taken up by the plant roots. Application of phosphorus influences the absorption and assimilation of a number of other essential as well as non-essential elements present in the soil. Its addition may have favourable (synergistic) or depressing (antagonsitc) effect on the availability of other nutrients. Generally, phosphorus and sulphur interaction was found to be synergistic on dry matter yield of different crops at their lower levels of application, but at their higher levels of application, there was antagonistic interaction effect (Aulakh et al., 1990; Islam et al., 2006).
 
The interaction of these elements may affect the critical levels of available phosphorus and sulphur, below which, the crop response to their application could be observed. Information on the effect of combined application of phosphorus and sulphur on their dynamics and nodulation in soil under black gram crop is rather limited in the subtropical zone of Jammu. It was very much essential to develop a strong workable and compatible package of phosphorus and sulphur management for black gram based on scientific facts and local conditions. However, the combined effect of phosphorus and sulphur on black gram has not yet been studied adequately in subtropical zone of Jammu. Keeping in view the above facts, the present study was undertaken to investigate the interaction effects of phosphorus and sulphur application on their dynamics and nodulation in soil in subtropical zone of Jammu.

The experiment comprising of four levels of phosphorus, i.e., 0, 20, 40 and 60 kg ha^-1 and three levels of sulphur, i.e., 0, 15 and 30 kg ha^-1, was conducted at Research Farm of the Division of Soil Science and Agricultural Chemistry, SKUAST-J, Main Campus, Chatha during summer of 2015-16 to investigate the interaction effect of phosphorus and sulphur application on their dynamics in soil. The crop was sown on April 6, 2015. The treatments were laid in randomized block design (Factorial) and replicated three times. The experimental site was subtropical endowed with hot and dry summer, hot and humid monsoon season and annual rainfall 1050-1133 mm, of which, about 75% was received from June to September. During the crop-growing period from April to July, the minimum temperature was 17.1°C and maximum 37.6°C, rainfall 173.22 mm and relative humidity 58.5%. The soil was sandy clay loam in texture, low in organic carbon, nitrogen and sulphur and medium in phosphorus and potash with pH 8.2 and EC 0.16 dSm^-1. The representative soil samples were collected from a depth of 0-15 cm. The soil samples were dried under shade and ground with a pestle-mortar and then sieved through 2 mm sieve and stored for further analysis. The physico-chemical properties (Table 1) of the soil were determined according to standard methods (Page, 1982; Bingham et al., 1982). The seed of black gram cv. Uttara was sown @ 20 kg ha^-1 in a plot size of 3 × 2 m², keeping a line spacing of 30 cm. All the recommended package and practices were adopted time to time for raising a healthy crop. In order to assess the dynamics of available and organic phosphorus and available and organic sulphur in experimental soil, a 200 g representative sample of soil from each treatment was collected 20 and 40 days after sowing and at maturity. The available phosphorus was estimated by using the method of Olsen et al. (1954) and organic phosphorus by hydrogen peroxide method of Jackson (1973). Available sulphur was estimated by turbidimetric method of Chesnin and Yien (1951) and organic sulphur as per the method of Williams and Steinbergs (1959) and sulphur in filtrate by turbidimetric method of Chesnin and Yien (1951). Five plants from each treatment was harvested at the time of flowering and root nodules from each plant were counted and average per plant was worked out. The data so obtained for available phosphorus, organic phosphorus, available sulphur, organic sulphur and number of root nodules plant^-1 were subjected to statistical analysis by using the method of Steel and Torrie (1980).
 

Available phosphorus (kg ha^-1)
 
The data shown in Table 2 indicate that the application of phosphorus significantly increased the available phosphorus at 20 DAS of black gram. The percent increase in available phosphorus with successive application of phosphorus 20, 40 and 60 kg ha^-1 over control in the absence of sulphur fertilization at 20 DAS of black gram was 63.17, 131.95 and 211.46, respectively. The maximum available phosphorus (63.85 kg ha^-1) was obtained at phosphorus level 60 kg ha^-1.
 

 
Further, the scrutiny of data depicts that available phosphorus showed decreasing trend after 40 days of black gram sowing at each successive phosphorus dose of 20, 40 and 60 kg ha^-1 over control in the absence as well as in the presence of sulphur fertilization. Data presented in Table 2 reveals that the application of each successive dose of sulphur had no significant effect on available phosphorus content at each successive dose of phosphorus at 20 and 40 DAS and at maturity of black gram.
 
The effect of different levels of phosphorus and sulphur application on available phosphorus (kg ha^-1) in soil is presented in Table 2. The higher values of available phosphorus with each successive application of phosphorus are attributed to higher availability of phosphorus.
 
Further, the scrutiny of data depicts that available phosphorus showed decreasing trend after 40 days of black gram sowing at each successive phosphorus dose of 20, 40 and 60 kg ha^-1 over control in the absence as well as in the presence of sulphur fertilization due to continuous uptake by black gram and fixation in soil. However, the application of successive doses of sulphur had no significant effect on available and organic phosphorus at each successive dose of phosphorus application at 20 and 40 DAS and at maturity of black gram. These results were in conformity with results of Randhawa and Arora (1997), Deshbhratar et al. (2010), Yadav (2011) and Dhage et al. (2014).
 
Organic phosphorus (kg ha^-1)
 
The effect of different levels of phosphorus and sulphur application on organic phosphorus (kg ha^-1) in soil is presented in Table 3. It is evident from the data that the application of phosphorus significantly increased the organic phosphorus in soil at 20 DAS of black gram. The percent increase in organic phosphorus with successive application of phosphorus (20, 40 and 60 kg ha^-1) over control in the absence of sulphur fertilization at 20 DAS of black gram was 7.89, 14.51 and 22.33, respectively. The maximum organic phosphorus (261.35 kg ha^-1) was obtained at phosphorus application of 60 kg ha-1.
 

 
The data further illustrate that organic phosphorus showed decreasing trend after 40 days of black gram sowing at each successive dose of phosphorus (20, 40 and 60 kg ha^-1) over control in the absence as well as in the presence of sulphur fertilization.
 
A perusal of data presented in Table 3 further reveals that the application of successive doses of sulphur had no significant effect on organic phosphorus at each successive dose of phosphorus at 20 and 40 DAS and at maturity of black gram.
 
The effect of different levels of phosphorus and sulphur application on organic phosphorus (kg ha^-1) in soil is presented in Table 3. The successive application of phosphorus significantly increased the organic phosphorus at 20 DAS of black gram. The percent increase in organic phosphorus with successive application of phosphorus (20, 40 and 60 kg ha^-1) over control in the absence of sulphur fertilization at 20 DAS of black gram was recorded as 7.89, 14.51 and 22.33, respectively. The maximum organic phosphorus (261.35 kg ha^-1) was obtained at phosphorus application of 60 kg ha-1. The higher values of organic phosphorus with successive application of phosphorus are attributed to higher availability of phosphorus with increasing dose.
 
Further, the scrutiny of data depicts that organic phosphorus showed decreasing trend after 40 days of black gram sowing at each successive dose of phosphorus application (20, 40 and 60 kg ha^-1) over control in the absence as well as in the presence of sulphur fertilization due to continuous uptake by black gram and fixation in soil. However, the application of successive doses of sulphur had no significant effect on organic phosphorus at each successive dose of phosphorus application at 20, 40 DAS and at maturity of black gram. Similar results were also reported by Deshbhratar et al. (2010), Yadav (2011) and Dhage et al. (2014).
 
Available sulphur (kg ha^-1)
 
The effect of different levels of phosphorus and sulphur application on available sulphur (kg ha^-1) in soil is presented in Table 4. It is indicated from the data that the application of sulphur significantly increased the available sulphur in soil at 20 DAS of black gram. The percent increase in available sulphur with sulphur application of 15 and 30 kg ha^-1 over control in the absence of phosphorus fertilization at 20 DAS of black gram was 112.71 and 238.90, respectively. The maximum available sulphur of 30.96 kg ha^-1 was obtained at sulphur application @ 30 kg ha^-1.
 

 
Further, the scrutiny of data portrays that available sulphur showed decreasing trend after 40 days of sowing and at maturity of black gram at each successive dose of sulphur (15 and 30 kg ha^-1) over control in the absence as well as in the presence of phosphorus fertilization. A perusal of data presented in Table 4 further reveals that the application of successive doses of phosphorus had no significant effect on available sulphur at each successive dose of sulphur @ 20 and 40 DAS and at maturity of black gram.
 
The effect of different levels of phosphorus and sulphur application on available sulphur (kg ha^-1) in soil is presented in Table 4. It is indicated from the data that successive application of sulphur significantly increased the available sulphur at 20 DAS of black gram. The higher values of available sulphur with the successive application of sulphur are attributed to higher availability of sulphur with increasing dose of sulphur.
 
Further, the scrutiny of data depicts that the available sulphur started decreasing after 40 days of black gram sowing at each successive sulphur dose of 15 and 30 kg ha^-1 over control in the absence as well as in the presence of phosphorus fertilization due to the continuous uptake by black gram and fixation in soil. However, the application of successive doses of phosphorus had no significant effect on available sulphur at each successive dose of sulphur at 20 and 40 DAS and at maturity of black gram. Similar results were also reported by Randhawa and Arora (1997), Deshbhratar et al. (2010), Yadav (2011) and Dhage et al. (2014).
 
Organic sulphur (kg ha^-1)
 
The data in Table 5 apparently show that the application of sulphur significantly increased the organic sulphur at 20 DAS of black gram. The per cent increase in organic sulphur with the successive application of sulphur (15 and 30 kg ha^-1) over control in the absence of phosphorus fertilization at 20 DAS of black gram was 3.26 and 6.96, respectively. The maximum organic sulphur of 301.67 kg ha^-1 was obtained when sulphur was applied @ 30 kg ha^-1.
 

 
A perusal of data depicts that organic sulphur showed decreasing trend after 40 days of black gram sowing at each successive dose of sulphur (15 and 30 kg ha^-1) over control in the absence as well as in the presence of phosphorus fertilization. Further, the scrutiny of data presented in Table 5 reveals that the application of successive dose of phosphorus had no significant effect on organic sulphur at each successive dose of sulphur at 20 and 40 DAS and at maturity of black gram.
 
The effect of different levels of phosphorus and sulphur application on organic sulphur (kg ha-1) in soil is presented in Table 5. It is indicated from the data that successive application of sulphur significantly increased the organic sulphur at 20 DAS of black gram. The higher values of available and organic sulphur with the successive application of sulphur are attributed to higher availability of sulphur with increasing dose.
 
Further, the scrutiny of data depicts that organic sulphur showed decreasing trend after 40 days of  black gram sowing at each successive dose of sulphur (15 and 30 kg ha^-1) over control in the absence as well as in the presence of phosphorus fertilization due to the continuous uptake by black gram and fixation in soil. However, the application of successive doses of phosphorus had no significant effect on organic sulphur at each successive dose of sulphur at 20 and 40 DAS and at maturity of black gram. Similar results were also reported by Deshbhratar et al. (2010), Yadav (2011) and Dhage et al. (2014).
 
Number of root nodules plant^-1
 
The significant increase in number of nodules with the increasing levels of phosphorus and sulphur were observed  in black gram. A perusal of the data in Table 6 revealed that the number of root nodules of black gram varied from a lowest value of 9.12 in control when no phosphorus and sulphur was applied to a highest of 23 when phosphorus 60 kg ha^-1 and sulphur 30 kg ha^-1 was applied in combination. The per cent increase in mean number of root nodules with the successive application of phosphorus @ 20, 40 and 60 kg ha^-1 over control was 24.24, 38.57 and 56.13, per cent respectively. The maximum mean number of root nodules plant^-1 of black gram (20.55) was obtained at phosphorus application of 60 kg ha^-1. These results were in agreement with the findings of Nawange et al., (2011) in chickpea, Yadav et al., (2012) in clusterbean, Togay et al., (2014) in lentil and Sarkar et al., (2017) in broad bean.
 

 
In the same way, the application of sulphur also significantly increased the number of nodules and the maximum mean number of nodules plant^-1 of black gram (20.04) was recorded at sulphur application of 30 kg ha^-1. Yadav (2011) in cluster bean also reported results in the same line indicating that the application of 40 kg P₂O₅ ha^-1 increased the number of nodules plant^-1 by 10.2 and 31.9% over 20 kg P₂O₅ and control and application of sulphur @ 20 kg ha^-1 increased number of nodules plant^-1 significantly over control and sulphur application of 10 kg ha^-1. The increase in number of nodules was 16.6% over control and 9.6% over sulphur application of 10 kg ha^-1. Similar results were also reported by Kachhava et al., (1997) and Chandra Deo and Khaldelwal (2009) in chickpea, Srinivasan et al., (2000) in black gram and Munshi et al., (2001) in groundnut.
 
Further, the data of Table 6 revealed that a significant interaction was found between phosphorus and sulphur and the optimum number of nodules plant^-1 of black gram i.e. 23.00 was recorded with combined application of phosphorus 60 kg ha^-1 and sulphur 30 kg ha^-1. The increase in number of nodules plant^-1 might be due to better root biomass with increasing levels of these nutrients. Phosphorus, being the constituent of nucleic acid and different forms of proteins, might have stimulated cell division resulting in increased growth of plants. Choudhary and Das (1996) reported beneficial effect of sulphur by lowering soil pH and improving physical condition of the soil. Yadav (2011) in the same crop found that interaction of phosphorus and sulphur significantly influenced number of nodules plant^-1. He reported maximum number of nodules plant^-1 at the highest level of phosphorus (40 kg P₂O₅ ha^-1) along with sulphur (30 kg S ha^-1). These findings are substantially close with those reported by Trivedi (1996), Tanwar et al., (2003), Chettri et al., (2004), Singh et al., (2006), Khatkar et al., (2007), Singh et al., (2008), Thesiya et al., (2013) and Kumawat et al., (2013) in black gram and Teotia et al .(2001), Das, S.K. (2017) and  Patel et al. (2018) in green gram.

Based on the results, it is concluded that the available phosphorus and organic phosphorus in soil increased significantly with the successive application of phosphorus but it started decreasing after 20 days of black gram sowing. The application of successive doses of sulphur had no significant effect on available and organic phosphorus. Similarly, the available sulphur and organic sulphur in soil increased significantly with the successive application of sulphur but it showed decreasing trend after 20 days of black gram sowing. The application of successive doses of phosphorus had no significant effect on available and organic sulphur. Number of nodules plant^-1 also increased significantly with increasing levels of phosphorus and sulphur up to highest level and the optimum values were recorded with combined application of phosphorus 60 kg ha^-1 and sulphur 30 kg ha^-1. Hence, it can be recommended to the farmers that the combined application of phosphorus 60 kg and sulphur 30 kg ha^-1 is the best option in addition to nitrogen 16 kg ha^-1 to improve the productivity of black gram and sustainability of soil in subtropical zone of Jammu division.

Authors are highly thankful to the Division of Soil Science and Agricultural Chemistry, SKUAST-Jammu for providing all necessary facilities to conduct this experiment.