Yield, nutrient uptake and soil enzyme activity of Bt cotton to intra row spacing and nitrogen management

Cotton cultivation has been steady in Telangana state since 2016. A field experiment was conducted at College farm, Professor Jayashankar Telangana Agriculture University, Rajendranagar, Hyderabad, Telangana during kharif to determine the effects of Bt cotton under varied plant densities and nitrogen levels on yield, plant nutrient uptake and soil enzyme status under high density planting system. The experiment was laid out in RBD with factorial concept consisting of four levels of planting densities of spacings viz., 90×15 cm2, 90×20 cm2, 90×30 cm2 and 90×60 cm2 as factor I treatments and 4 levels of nitrogen viz., 90, 120, 150,180 kg N ha-1 as factor II treatments and replicated thrice. The result shows that with the wider spacing of 90 x 60 cm (18,518 plants ha⁻¹) recording the highest boll weight (5.10 g), while the closer planting of 90 x 15 cm (74,074 plants ha⁻¹) resulted in the lowest boll weight (4.41 g). However, seed cotton yield per hectare increased with planting density, with 90 x 15 cm spacing showing a 34.1% higher yield compared to 90 x 60 cm. Nutrient uptake was also highest at 90 x 15 cm spacing, recording 57.8, 29.0 and 117.9 kg ha-1 of nitrogen, phosphorus, and potassium, respectively at the first picking stage. Regarding nitrogen levels, the application of 150 kg N ha-1 resulted in significantly higher boll weight (4.87 g) and seed cotton yield (2072 kg ha-1). While, higher nutrient uptake was recorded with 180 kg N ha-1 compared to 90 kg N ha-1. Seed cotton yield projected an increase of 13.4% to 21.5% with the higher nitrogen doses, though further increases in nitrogen beyond 150 kg N ha-1 did not significantly improve yields. Soil enzyme activities, including urease and dehydrogenase, showed minimal variation with planting density, although higher enzyme activity was observed at the closer spacing of 90 x 15 cm and at higher nitrogen levels, reflecting improved soil nutrient availability and microbial activity. The interaction between planting density and nitrogen levels was found to be non-significant for all measured parameters.