Site Specific Nutrient Management for Increasing Soybean Production

The field experiment was conducted in field at Regional Research Center, Amravati during kharif season in 2018-19. The experiment was laid out in Randomized block design with three replications consisting of seven treatments. Based on inputs nutrient application rate 25:32:32 kg/ha N:P2O5:K2O comprising of T1: SSNM basal recommendation through nutrient expert (35:49:43 NPK kg/ha), T2: T1 – N Omission (00:32:32 NPK kg/ha), T3: T1 – P Omission (25:00:32 NPK kg/ha), T4: T1 – K Omission (25:32:00 NPK kg/ha), T5: RDF (NPKS) (30:75:30:20 NPK S kg/ha), T6: Farmers practice (23:58:00 NPK kg/ha), T7: Absolute control. The observation on Yield attributes viz., pods per plant, seed index, seed yield kg/ha, straw yield kg/ha and harvest index was recorded at the time of harvesting. Significantly highest no. of pods per plant (19.00) was recorded with application NPK. The mean of test weight was (10.73 g) found to be highest with the ample application of NPKS. The significantly highest seed yield (1718 kg ha -1 ) was recorded with application of NPKS followed by omission of K (1517 kg ha -1 ) while lowest seed yield (1115 kg ha -1 ) was recorded under absolute control and omission of Phosphorus (1296 kg ha -1 ). The mean straw yield recorded was significantly highest (2111 kg ha 1 ) under combined application of NPKS whereas lowest straw yield (1443 kg ha-1) was registered in treatment absolute control. The treatment with RDF (NPKS) recorded higher net returns and higher B: C ratio.


INTRODUCTION
Soybean has already established as one of the substitute crop for major kharif cash crop. The improved production technology has increased the productivity of soybean. There are various package of practice has developed for increasing soybean production. Now a day's most of the farmers are alert regarding adoption of recommended dose of fertilizer, incorporation of FYM, compost and crop residues as well as seed treatment with biofertilizers etc. for getting maximum yield. The major concern today is the low productivity of soybean and one of the major concerns of low productivity is declining soil fertility.
Continuous use of imbalance fertilizers has resulted in macro and micro nutrient deficiencies and is consider as the most important factor for low productivity of soybean after water management. The existing fertilizer recommendation for soybean often consists of fixed rates and timing of N, P and K for vast areas of production. Such recommendations are constant over the years over large areas. But crop growth and crop need for supplemental nutrients are strongly influenced by crop growing conditions, crop and soil management and climate which can vary greatly among field, season and year (Umesh et al., 2014).
The SSNM (Site Specific Nutrient Management) approach does not significantly aim to either reduce or increase fertilizer use. Instead, it aims to apply nutrients at optimal rates and times in order to achieve high yield and high efficiency of nutrient use by the crop, leading to high cash value of the harvest per unit of fertilizer invested (Shankar & Umesh, 2008). Considering the fertilizer cost and availability, this limited resource needs to be saved for sustainable crop production through improving the nutrient use efficiency by site specific application. The concept of site specific nutrient management (SSNM) for crop emerged in the mid-1990s. Site specific nutrient management (SSNM) is a set of scientific principles for optimally supplying essential nutrients (Umesh et al., 2014). We need SSNM mainly for increasing nutrient use efficiency and profitability. Therefore, an experiment was conducted with the objective to study the bridging yield gap of soybean through site specific nutrient management (SSNM).
After seed bed preparation, sowing Soybean cv JS-95-60 was done by dibbling. The net plot size was 5.0 m x 2.7 m. The observation on Yield attributes viz., pods per plant, seed index, seed yield kg/ha, straw yield kg/ha and harvest index was recorded at the time of harvesting.

RESULTS AND DISCUSSION Yield attributes
The number of pods per plant ranged 14.53 to 19.00. Significantly highest no. of pods per plant (19.00) was recorded with application NPKS followed by omission of K (17.60) while lowest number of pods per plant (14.53) was recorded under absolute control and omission of Phosphorus (14.73). The seed index of soybean seed at harvest stage varied from 9.71 to 10.73. The mean of test weight was (10.73 g) found to be highest with the ample application of NPKS. The test weight of soybean seed in NPK omission treatments indicated that the nutrients are required in balanced quantity. Nath et al. (2012) reported similar results with the application of NPK.
Growth and biomass production were strongly influenced by indigenous nutrient supply and the nutrients supplied through fertilizers. This was reflected in yield parameters, seed and straw soybean yield ( Table 1). The seed yield of soybean ranged from 1151 to 1718 kg ha -1. The significantly highest seed yield (1718 kg ha -1 ) was recorded with application of NPKS followed by omission of K (1517 kg ha -1 ) while lowest seed yield (1115 kg ha -1 ) was recorded under absolute control and omission of Phosphorus (1296 kg ha -1 ). Thus indicates the importance of phosphorus in soybean crop and its sensitivity to phosphorus. The seed yield was decrease due to omission phosphorus, omission of nitrogen and omission of potassium over combined application of NPK.
Highest yield gap over SSNM treatment was observed in control treatment of P omission treatment i.e. 206 kg/ha while least yield gap over RDF was noticed in K omission treatment (-201 kg/ha) ( Table 2). The higher seed yield with the combined application of NPK could be attributed to adequate supply of nutrients through balanced nutrient management system which helped for proper growth and yield attributes and led higher grain yield. Kolo et al., (2012) also reported similar findings. Katkar et al. (2012) and Janjilwad et al. (2019) recorded significantly highest yield of soybean by the application of NPK. The straw yield of soybean at harvest stage varied from 1443 to 2111 kg ha -1 . The mean straw yield recorded was significantly highest (2111 kg ha -1 ) under combined application of NPKS whereas lowest straw yield (1443 kg ha-1) was registered in treatment absolute control. The highest straw yield in balanced NPK might be ascribed due to enhanced nutrient uptake and efficiency of nutrients. The results are in line with the findings reported by Singh et al. (2001). The highest harvest index was observed in K omission treatment.

Economics in soybean
Economics is an important factor that determines practical utility/ feasibility of the technology in crop production. Different nutrient management practices increased seed yield accordingly net returns and benefit cost ratio. The treatment with RDF (NPKS) recorded higher net returns and higher B: C ratio. Need based application of fertilizers to the crop under SSNM might have led to the higher production. Hence higher net returns and B: C ratio than control were observed under NPKS approach. Biradar et al. (2006) made similar observation in wheat, rice and chickpea crops. Lower net returns and B: C ratio was recorded in Absolute control.