Sustaining cotton productivity and soil fertility through in situ management of green manure and crop residues in semi-arid irrigated condition of Tamil Nadu

A field experiment was undertaken between 2004 and 2007 in upland cotton (Gossypium hirsutum L.) on alkaline black clay loam Typic haplustalfs soil with low fertility at Coimbatore under irrigated condition to explore the suitability of burying of cotton residues vis-à-vis green manure (GM) sunnhemp (Crotalaria juncea L.) in situ. The treatments to cotton ‘Surabhi’ included in situ growing and burying of GM crop, recycling of cotton residues and addition of farmyard manure (FYM) alone and in all combination (@ 5 t/ha of FYM, 2.5 t/ha of crop residues or GM @ 15 kg seed/ha), along with conventional practice of crop nutrition with and without a N:P:K dose of 60:13:25 kg/ha as the controls. Results revealed that simultaneous planting of sunnhemp and cotton under ridge-furrow system, followed by burying of sunnhemp @ 2.5 t/ha in situ before flowering followed by earthing up was optimum for higher cotton productivity (1.70 t/ha), net return (Rs 23,240/ha), B:C ratio (1.37) and fibre productivity efficiency (FPE, 9.40 kg/ha-day). However, grain yield of rotational finger millet [Eleusine coracana (L.)] ‘CO 13’ crop grown on the residual fertility was not influenced by the treatments.The system (cotton-finger millet) productivity (2.46 t/ha) was also favoured by GM treatment. Soil fertility parameters after the trial indicated that in situ incorporation of GM also resulted in higher OC (0.53, 0.55%) and N:P:K (200:23.5:599 and 194:18.3:590 kg/ha) availability in 0–15 cm and 15–30 cm soil respectively at the end of 3 years of cropping over absolute control. Climatologically favourable year (2007) played a significant role in realization of higher boll weight, seed cotton yield, net return, B:C ratio and system productivity over others. The present study suggests that in situ incorporation of sunnhemp GM substitute inorganic fertilizers in cotton.