Influence of nitrogen management on expression of cry protein in Bt-cotton (Gossypium hirsutum)

To assess the requirements of nitrogen (N), schedule of N application, detopping in Bt-cotton (Gossypium hirsutum L.) and their effects on cry protein concentration, other related parameters and yield were studied by conducting field experiment at Dharwad for 2 years (2005–06 and 2006–07) under irrigated conditions. Present study indicated that N fertilization significantly affected cry protein concentration in leaf at various growth stages. At 60 days after sowing (DAS) increased level of nitrogen from 120 and 160 kg N increased cry protein by 9.3 and 14.8% over 80 kg/ha. Leaf nitrogen concentration and SPAD readings followed same pattern as that of cry protein concentration. Application of N in 7 splits significantly improved the cry protein level (5043 ng/g) over either N applied in 4 splits (4066 ng/g) or recommended practice of three splits (3583 ng/g). Studies also indicated that increasing level of nitrogen from 80 to 120 and further to 160 kg/ha significantly increased seed cotton yield by 12 and 19%, respectively. Application of nitrogen with recommended method of 3 splits (2.27 t/ha) and N applied in 7 splits at 15 days interval (2.24 t/ha) produced on par yields. There was no beneficial and significant effect of detopping in Bt-cotton at different growth stages.