Response of Bt cotton (Gossypium hirsutum) hybrids to irrigation

Abstract

A field experiment was conducted during 2006–07 at New Delhi to study the performance of 2 Bt cotton (Gossypium hirsutum L.) hybrids in relation to irrigation schedules based on irrigation water (IW)/cumulative pan evaporation (CPE) with an IW of 60 mm. Over the years, ‘MRC 6304’ and ‘RCH 317’ gave similar seed cotton yield (2.31 tonnes/ ha) and net returns (Rs 30 165/ha). Irrigation of cotton at 0.6 IW/CPE ratio being on par with 0.4 IW/CPE ratio throughout crop duration recorded taller plants with more boll number (45.4) and higher boll weight (4.34 g), finally resulting in higher seed cotton yield (2.55 tonnes/ha) over 0.2 IW/CPE ratio throughout crop duration (2.20 tonnes/ha) and the crop irrigated at 0.4 IW/CPE ratio till onset of monsoon (2.05 tonnes/ha). The highest stalk yield was recorded with crop irrigated throughout at 0.6 IW/CPE ratio being significantly higher over all other irrigation treatments; the lowest being with crop irrigated at 0.4 IW/CPE ratio till onset of monsoon. Further irrigation 0.6 IW/CPE ratio fetched an additional net income of Rs 1 500/ha over 0.4 IW/CPE ratio throughout crop duration. Irrigation at 0.2 IW/CPE ratio also gave higher productivity and income over post-monsoon rainfed crop (0.4 IW/CPE irrigation from sowing to onset of monsoon). The data on mean consumptive use moisture extraction pattern and water productivity indicate that both the Bt hybrids behaved similarly to these parameters. Increasing IW/CPE ratio from post-monsoon rainfed (0.4 IW/CPE irrigation from sowing to onset of monsoon) to the highest of 0.6 IW/CPE ratio throughout the crop duration increased consumptive use, while water productivity based on consumptive use and quantity of irrigation water applied and marginal productivity were the highest with post-monsoon rainfed crop. Cotton irrigated at 0.4 and 0.6 IW/CPE ratio recorded more water extraction from top 60 cm, while crop irrigated throughout at 0.2 IW/CPE and post-monsoon rainfed crop extracted more water from deeper layers of soil (60–180 cm).