Direct and residual effects of nitrogen management in Bt cotton (Gossypium hirsutum)-wheat (Triticum aestivum) cropping system

A 2-year field investigation was carried out in New Delhi from 2006 to 2008 on a sandy loam soil having 217 kg/ha of available N. In cotton (Gossypium hirsutum L.) 8 treatments comprising combination of 4 N management practices {Control, 100% recommended dose of N (150 kg/ha) through urea (RDN), 75% RDN through urea + 25% RDN through FYM N and 50% RDN each through urea and FYM) and 2 cropping systems - sole cotton and cotton + groundnut (Arachis hypogaea L.) intercropping in 1:3 additive series. N management in cotton-wheat cropping system were tested in RBD with 3 replications. For comparison, sole groundnut with recommended N and phosphorus fertilizers was also grown. In rabi, cotton plots were sub-divided in to 4 to accommodate levels of N (0, 50, 100 and 150 kg/ha) to wheat. Groundnut as an intercrop enhanced the productivity of cotton by 0.25 tonne/ha and succeeding wheat by 0.16 tonne/ha. These increases in productivity of cotton and wheat coupled with additional intercrop groundnut yield (0.47 tonne/ha) together enhanced the productivity of cotton + groundnut - wheat systems in seed cotton equivalent yield by 0.58 tonne/ha and net returns by Rs 14,421/ha over cotton-wheat system. Among N management practices, substitution of 25% RDN through FYM in cotton gave the highest system productivity (4.82 tonne seed cotton equivalent yield/ha) and B: C ratio (2.09) than all N through urea and 50% N through each source. However, net returns and soil N balance were in favour of 50% RDN substitution through FYM besides (Rs 72,748/ha). Wheat crop responded to100 kg N/ha fertilization. It was therefore inferred that integration of groundnut as intercrop along with FYM besides 50% N of cotton along with 100 kg fertilizer N/ha to wheat was the most profitable and sustainable N management system.