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

Abstract

A 2-year field investigation was carried out in New Delhi from 2006 to 2008 on a sandy loam soil having 217 kglha of available N. In cotton (Gossypium hirsutum L.) 8 treatments comprising combination of 4 N management practices {Control, 100% recommended dose of N (1 50 kglha) 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 tonnetha and succeeding wheat by 0.16 tonnetha. These increases in productivity of cotton and wheat coupled with additional intercrop groundnut yield (0.47 tonnelha) together enhanced the productivity of cotton + ground- nut - wheat systems in seed cotton equivalent yield by 0.58 tonnetha and net returns by R s 14,421 /ha over cot- ton-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 yieldlha) 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 sub- stitution 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 fer- tilizer N/ha to wheat was the most profitable and sustainable N management system.