Indigenous Nutrient Supplying Capacity of Vertisols under Cotton and Soybean

This project was aimed at determining the response of cotton and soybean to major nutrients, and understanding the extent of spatial and temporal variability of yield responses across the soybean and cotton-growing regions of Maharashtra. The study compared four treatments: 1) ample NPK (nitrogen, phosphorus, and potassium) 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. The study determined the nutrient uptake pattern, nutrient use efficiency and residual soil fertility through the nutrient omission technique. The results of the study contributed to the development of the Nutrient Expert® fertilizer decision support tools for cotton and soybean.

Average yield data pooled over three years indicated that the ample NPK treatment produced the highest soybean (2.1 t/ha) and cotton (2.4 t/ha) yields. The lowest soybean yield was recorded with the P omission (1.6 t/ha), a yield reduction of 22% over the ample treatment. The yield reductions due to N and K omission were 18% and 9%, respectively. The lowest seed cotton yield was recorded with N omission (1.9 t/ha), and the yield reductions over the ample treatment were 19% for N omission, followed by K (13%) and P (9%) omission. The highest soybean and seed cotton yields in the ample NPK treatment was associated with high N, P, and K uptakes, 132.7, 22.8, and 59.6 kg/ha and 85.4, 23.9, and 92.3 kg/ha, respectively.

Agronomic efficiency (AE: kg grain per kg nutrient applied) of N, P, and K were 12.3, 4.6, and 2.4 for soybean; and 2.4, 2.9, and 3.3 for cotton, respectively. The low agronomic efficiencies observed is typical for omission plot studies where nutrients are applied in ample quantities to ensure none of the nutrients are limiting except the intended ones. The study was concluded in 2016 and the results of the study were used for the development of Nutrient Expert for soybean and cotton.