[Effects of irrigation amount and frequency on soil water distribution and water use efficiency in a cotton field under mulched drip irrigation].

A 2-year (2009 and 2010) field experiment was carried out to investigate the effects of irrigation amount (300, 375, and 450 mm) and irrigation frequency (once every 3-, 7-, and 10 days) on the soil water distribution and cotton water use efficiency (WUE) under mulched drip irrigation in North Xinjiang. When the irrigation amount was 375 mm, irrigation once every 3 days induced a higher water content in surface soil (0-20 cm) in the whole growth season of cotton but made the deeper (below 40 cm) soil not moistened enough. Irrigation once every 10 days benefited the irrigation water penetrated downward or sideways and made the deeper soil have a higher water content; however, this drip irrigation did not replenish water in time, and made the surface soil water content lower. Overall, drip irrigation once every 7 days benefited the uniform distribution of irrigation water in soil profile. Under the same irrigation frequencies, the larger the irrigation amount, the higher the soil water content. The cotton water consumption in all treatments had the similar pattern, i. e., lower at seedling stage (averagely < 1.7 mm x d(-1)), increased gradually since squaring stage and reached the maximum at full bloom stage (about 8.7 mm x d(-1)), and decreased at onen-boll staue (about 1.0 mm x d(-1). Under the natural condition, the total cotton water consumption had close correlation with irrigation amount but poor correlation with irrigation frequency, and the cotton WUE decreased significantly with increasing irrigation amount. When the irrigation amount was 300 mm, the WUE was higher but the yield production decreased markedly, whereas excessive irrigation (450 mm) had no significant yield-increasing effect but wasted water. It was suggested that irrigation with an amount of 375 mm and a frequency of once every 7- or 10 days could be an appropriate drip irrigation mode for the local cotton field under natural condition.