Evaluating Bt cotton (Gossypium hirsutum L.) under different management practices

Abstract

Removal of early fruiting branches with optimum/higher nitrogen and potassium dose can cause more source and no sink at early stages leading to delay in onset and progression of senescence in Bt cotton. The present investigations were carried out to find out interactive effect of square/fruiting branch removal in Bt cotton cultivar IR-3701 using different nitrogen and potassium doses. Two experiments were planted during 2011 and repeated during 2012 at the Agronomic Research Area, University of Agriculture Faisalabad. First experiment comprised of manual alteration of plant architecture i.e. F1: no fruiting branch removal, F2: removal of first fruiting branch, F3: removal of first and second fruiting branch, F4: removal of all squares (floral bud) from first fruiting branch, F5: removal of all squares from first and second fruiting branch; and three nitrogen rates i.e. N1: 175, N2: 225 and N3: 275 kg ha-1. Removal of first and second fruiting branch and removal of all squares from first and second fruiting branch along with increasing nitrogen dose improved yield, yield components and quality of cotton as well as helped in delayed onset of senescence and in increasing Cry1Ac concentration in boll pericarp; but on the basis of marginal rate of return, removal of first and second fruiting branch with medium level of nitrogen application (225 kg N ha-1) was the best treatment combination. In second experiment manual alteration of plant architecture (same treatments as in experiment 1) was combined with three potassium rates i.e. K1:50, K2: 100 and K3: 150 kg K ha-1. Results showed that removal of first and second fruiting branch and removal of all squares from these branches at higher level of potassium application (150 kg K ha-1) improved yield, yield components and quality traits, reduced premature senescence and also improved Bt gene expression in late season by increased uptake of N and K in plant. Highest BCR as well as maximum MRR were obtained by supplying the crop with 150 kg K ha-1 and removing first and second fruiting branches at early stages.