Abstract:
Abstract: Cotton is an important cash crop widely planted in the northwest arid area of China where plastic films have long been coupled with drip irrigation in crop cultivation to keep soil moisture and raise crop yield. However, as plastic films are difficult to degrade, the so-called white pollution caused by film residuals left in the soils has become an ever severer issue in cotton fields in arid areas due to long time use of plastic films and ineffectiveness of the recycle measures. In contrast to plastic films, liquid mulch, an organic polymer, is environmental friendly because it degrades naturally. To find out the feasibility of replacing plastic films with liquid mulch in drip irrigated cotton fields and the appropriate dosage of liquid mulch for optimal plant physiological characteristics and in turn crop yield, a bucket experiment was conducted on drip irrigated cotton. A total of five treatments were set up including 3 treatments with liquid mulch at different dosages, 1900 kg/hm2 (LFD1), 2200 kg/hm2 (LFD2), and 2500 kg/hm2 (LFD3), one treatment with common plastic film (PFD) and a bare soil control (CK) without liquid mulch or common plastic film. The influence of liquid mulch on the physiological characteristics (i.e., leaf net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO2 concentration), water use efficiency (WUE), yield components (i.e., boll number per plant and single boll weight) and cotton yield was monitored and analyzed. The results showed that liquid mulch dosage had important influence on the physiological characteristics indexes, WUE and cotton yield. With increase in liquid mulch dosage, leaf net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration and yield increased and became closer to those in PFD. The influence of liquid mulch on the physiological characteristics of drip irrigated cotton was more significant in the early and middle growth stages of cotton when physiological activities were active and became less significant with time in the late growth stage of cotton. Leaf net photosynthetic rate was significantly higher (P<0.05) in the 3 treatments with liquid mulch (i.e., LFD1, LFD2 and LFD3) than in CK at all the measuring times; liquid mulch at different dosages had different influences on leaf net photosynthetic rate in different cotton growth stages or at different measuring time periods of a same growth stage. Leaf net photosynthetic rate in LFD1, LFD2 and LFD3 measured at 14:00 of June 26 when cotton was in its bud stage with relatively vigorous physiological activities was 11.12%, 29.76% and 40.20% higher, respectively, than in CK but 24.96%, 12.38% and 5.33% lower, respectively, than in PFD; WUE, boll number per plant, single boll weight and yield in treatments with liquid mulch were significantly higher (P<0.05) than those in CK but these indexes were not significantly different (P>0.05) between the treatment with the highest dosage (2500 kg/hm2) of liquid mulch (LFD3) and PFD. Cotton yield in LFD1, LFD2 and LFD3 was 7.10%, 11.79% and 14.39% higher, respectively, than in CK. Liquid mulch at different dosages had important influences on the WUE and yield of drip irrigated cotton, and liquid mulch influenced cotton WUE and yield by continuously influencing its physiological characteristics. An appropriate amount of liquid mulch (not less than 2500 kg/hm2) coupled with drip irrigation had comparable water-saving and yield-increasing effects (relative to the bare soil control) to plastic film coupled with drip irrigation. Liquid mulch can replace plastic films in drip irrigated cotton fields without sacrificing crop yield. In addition, the natural degradability and pollution-free feature of liquid mulch provides a promising approach to address the white pollution issue in cotton fields of arid and semiarid areas.