Mechanism of premature senescence of cotton plants grown under drip irrigation and mulch film : plant growth response and nutrient status

A field experiment was conducted to investigate the mechanism of premature senescence of cotton plants grown under drip irrigation and mulch film (DI) compared with flooding irrigation (FI) in 2009 and 2010. Plants showed severe premature senescence symptoms at advanced growth stages under DI but not under FT. The K content of upper leaves in the canopy was lower under DI than FI. At the late bolls stage, shoot biomass under DI was significantly higher than under FI, whereas root biomass showed the opposite trend. Root length density in the 0-10 cm soil layer was higher under DI than and total root length decreased after 125 DAS under DI. The soil available K content decreased significantly after the onset of flowering. The soil available K content decreased as root length density increased within the range 0-2 m 1000/cm(3). It suggested that the premature senescence under DI was attributable to the increased shoot K demand exceeding the roots' capacity to supply K, and localized soil K deficiency caused by the shallow root distribution coupled with decreased root length, which impeded the K absorption capacity of the plant.