Response of American cotton (Gossypium hirsutum) to methods of irrigation and levels of phosphorus under shallow ground water-table condition.

Afield experiment was conducted during the rainy (kharif) seasons of 2002-04 at Khetawali Distributary, Hanumangarh, Rajasthan to study the yield, benefit: cost ratio and water-use efficiency of 'RS 2013' American cotton (Gossypium hirsutum Linn.) variety under high ground water-table conditions. Among the methods of irrigation, flood irrigation gave significantly highest seed cotton yield (2.44 tonnes/ha), monopodials/plant (8.7) and sympodials/plant (14.6) compared to furrow, alternate furrow and alternate furrow in rotation irrigation treatments. Height (170.3 cm), boll/plant (80.5) and boll weight (3.39 g) recorded with flood irrigation were higher but at par with furrow irrigation and superior to rest of the irrigation treatments. Similarly, flood irrigation gave the highest water use (384.3 mm), benefit: cost ratio (3.70) and sustainability yield index (86.54%) than all other irrigation methods. However, highest water-use efficiency of 6.55 kg/ ha-mm was recorded with furrow irrigation in rotation. Between the 2 phosphorus levels 22.5 kg P/ha gave significantly higher seed cotton yield (2.19 tones/ha), sympodial/plant (13.3), boll/plant (75.3), boll weight (3.30) and higher sustainability yield index (79.82%) and benefit: cost ratio (3.25). Water-table depth was the lowest at sowing in most of the years, thereafter water-table went down up to end of October and then it fell suddenly at harvest. Electrical conductivity (EC) of soils at harvest was highest with irrigation in alternate furrow, followed by alternate furrow in rotation, furrow and flood irrigation method. EC of groundwater was slightly higher at furrow irrigation in alternate rows, and furrow irrigation in alternate rows in rotation compared to flood and furrow irrigation treatments. The pH of the soil at harvest and groundwater at active growing stage was not affected by irrigation methods.