Indigenous Nutrient Supplying Capacity of Vertisols under Cotton and Soybean

A set of on-farm trials were initiated during 2015 in Rahit and Donad villages in Barshitakli tehsil and Warudi, Dhotardi, and in Waki village in Akola tehsil, Akola district, Maharashtra to assess the N, P and K responses in soybean and cotton. The trials compared four treatments: 1) ample NPK and other limiting nutrient application, 2) omission of N from the ample treatment, 3) omission of P from the ample treatment, and 4) omission of K from the ample treatment. Soybean was grown under rainfed conditions, while cotton was grown under both rainfed as well as with supplementary irrigation.
The grain yield of soybean varied from 1.2 to 2.6 t/ha across locations and treatments. Highest mean grain yield (2.0 t/ha) was recorded in the ample NPK treatment, followed by K omission (1.8 t/ha). The highest grain yield reduction (22%) was observed in the P omission treatment followed by N omission (14.5%). This indicates that the soybean grain yield was influenced mostly by P. The highest plant height (58 cm), pods (39) and nodules (37) were recorded in the ample NPK treatment, while omission of N, P, and K significantly reduced these parameters. The highest N uptake (147 kg/ha), P uptake (19 kg/ha), and K uptake (64 kg/ha) was also observed in the ample NPK treatment. The available N (230 kg/ha), P₂O₅ (15 kg/ha), K₂O (450 kg/ha), and S (16 kg/ha) in the post-harvest soil samples were recorded in the ample NPK treatment. Seed cotton yield ranged from 1.2 to 3.0 t/ha at all the locations and highest mean seed cotton yield (2.4 t/ha) was recorded in the ample NPK treatment, while the lowest was under N omission (2.0 t/ha). A significantly higher number of bolls and boll weight were also recorded in the ample NPK treatment, while they were lowest under N omission.

Cotton and soybean are major crops cultivated on large tracts in India. Unbalanced and inadequate nutrient application in these crops are a major concern as it affects profitability of smallholder farmers. The current work is a part of the initiative to develop the Nutrient Expert® fertilizer decision support tool for these crops that are now being supported by multiple research partners in India.