Nutrient requirement of Bt. cotton (Gossypium hirsutum)

Abstract

A field experiment was conducted on Ver tisols of Dharwad, Karnataka during the rainy seasons of 2007 and 2008, to ascertain the nutrient requirement of Bt cotton ( Gossypium hirsutum L.) with the recommended dose of fertilizer (RDF, 1206060 kg N P O K O/ha) advocated to the conventional non-Bt cotton hybrid. The investiga- 2 5 2 tion focused on varying the recommended nitrogen application levels into 7 splits10% as basal, remaining 90% in equal splits at 30, 60, 75, 90, 105 and 120 days after sowing (DAS)with entire dose of P and K coupled with the soil application of MgSO @ 25 kg/ha, foliar nutrition of urea (2%), DAP (2%), MgSO (1%), KNO (2%), calcium 4 4 3 nitrate (1%), multimicronutrient (1%), Cytokinin (2 ppm) and polyethylene mulching (100 micron thickness). Bunny Bt (NCS 145) cotton genotype was sown with 90 cm 60 cm spacing. Foliar application of KNO 2%, soil 3 and foliar application of MgSO @ 25 kg/ha and 1% respectively, and soil application of MgSO @ 25 kg/ha alone 4 4 increased the seed-cotton yield by 25.0, 24.4 and 24.3% respectively, over the RDF. Sympodial branches and total number of bolls/plant followed the similar trend. At 120 DAS, increase in leaf potash content (1.02%) was recorded with foliar application of 2% KNO and the increase in leaf magnesium (1.86%) was noticed with soil and foliar ap- 3 plication of MgSO @ 25 kg/ha and 1% respectively. Significantly increased 2.5% span length (33.1 mm) and 4 bundle strength (24.8 g/tex) were observed with foliar application of KNO (2%) over the other treatments. Foliar 3 application of KNO (2%) (3 sprays on 15 October, 1 November and 31 November) significantly increased the 3 seed-cotton yield (2.54 t/ha), gross returns ( 56.2 103/ha), net returns ( 27.8 103/ha) and benefit: cost ratio (1.98).