Methods of cotton (Gossypium hirsutum) establishment and zinc fortification in cotton-based cropping systems: Direct and residual effect on onion (Allium cepa) and system productivity of cotton-onion cropping system

A field experiment was conducted during rainy (kharif) and winter (rabi) seasons of 2013–14 and 2014–15 at New Delhi, to evaluate the effect of 2 methods of cotton establishment (direct sowing and transplanting) and 5 zinc-levels (control, 2.5, 5.0, 7.5 kg Zn/ha and 0.5% zinc sulphate foliar spray at 60 and 90 days after planting) on cotton (Gossypium hirsutum L.) and their residual and direct effect of 5.0 kg Zn/ha in place of foliar treatment on the succeeding wheat [Triticum aestivum (L.) emend. Fiori & Paol.] and onion (Allium cepa L.) crop. In this research paper residual effect of treatments applied to cotton and direct effect of Zn on onion has been presented along with system productivity and resource-use efficiency. Productivity of cotton and onion was higher during 2013–14 than 2014–15. Onion recorded significantly higher economic parameters and nutrient uptake after transplanted cotton than direct sown. Onion produced statistically similar growth and yield attributes, bulb yield, gross and net returns and nutrient uptake, due to direct application of 5.0 kg Zn/ha and residual effect of 5.0 and 7.5 kg Zn/ha to cotton, which were significantly superior to control and residual effect of 2.5 kg Zn/ha. Based on 2 years average, gain in net returns was 40, 350, 43, 200 and 47, 950/ha due to residual effect of 5.0/7.5 kg Zn/ha and direct effect of 5.0 kg Zn/ha over control. Both residual and direct effect of Zn found to enhance the quality of bulb in terms of Zn enrichment and on an average 32.0, 31.8% and 36.2% increase in Zn uptake was recorded due to residual effect of 5.0/7.5 kg Zn/ha and direct effect of 5.0 kg Zn/ha respectively. Based on 2-years average, system productivity in terms of seed cotton equivalent yield (9.45 t/ha), production efficiency (27.0 kg/ha/day), economic efficiency (736.9 /ha/day) and irrigation water productivity (1.16 kg/m³) of transplanted cotton-onion cropping system was significantly greater than the direct sown cotton-onion system. Successive increase in Zn-levels caused significant increase in system productivity, production efficiency, economic efficiency and irrigation water productivity up to application of 5.0 kg Zn/ha. So based on the study it is concluded that in Bt cotton-onion cropping systems 5.0 kg Zn/ha to Bt cotton is sufficient to meet the zinc requirement of both the crop and transplanted cotton is better than direct sown cotton.