Enhancing Bt cotton productivity through in-situ green Manuring, optimized irrigation regimes and micronutrient management in Vertisols of the Malaprabha command area

Abstract

The study was undertaken to evaluate the effects of in-situ green manuring, irrigation regimes, and micronutrient management on yield, water use efficiency, and soil fertility status of Bt cotton grown in a Vertisol of the Malaprabha Command Area. A long-term factorial experiment was conducted from 2014- 15 to 2017- 18 at the AICRP on Irrigation Water Management Research Centre, Belavatagi, using a split-plot design. The experiment comprised three irrigation levels in the main plots, namely I1 and I2 at 0.8 and 0.6 IW/CPE ratios, respectively, and I3 based on critical growth stages. Sub-plots consisted of five nutrient management treatments: F1 (100% recommended dose of fertilizers with FYM at 10 t ha⁻¹), F2 (F1 plus one row of sunhemp grown between two rows of Bt cotton), F3 (F2 plus application of ZnSO₄ at 25 kg ha⁻¹, FeSO₄ at 25 kg ha⁻¹, and borax at 5 kg ha⁻¹), and F4 and F5 which included 75% and 50% RDF, respectively, along with FYM at 10 t ha⁻¹, biofertilizers, one row of sunhemp between Bt cotton rows, micronutrients (ZnSO₄, FeSO₄, and borax at the above rates), and maize stalk incorporation at 10 t ha⁻¹. Pooled results indicated that irrigation level I1 (0.8 IW/CPE) recorded a significantly higher kapas yield (19.01 q ha⁻¹) compared to irrigation scheduled at critical stages (I3), which yielded 16.17 q ha⁻¹. Among nutrient management practices, F3 resulted in significantly higher kapas yield (21.65 q ha⁻¹) and water use efficiency (3.69 kg ha⁻¹ mm⁻¹). Soil analysis data collected during 2016- 17 and 2017- 18 revealed no significant differences in soil pH and electrical conductivity; however, significant improvements were observed in organic carbon content and the availability of P₂O₅, K₂O, and zinc under integrated nutrient management treatments.