Effects of plastic film residue rate on root zone water environment and root distribution of cotton under drip irrigation condition

Abstract：Plastic film is a key technology of improving agricultural yield in water-shortage area. Root system is an important organ to obtain water and nutrients, and it affects production efficiency of crops through the interaction of root zone environment. The objective of this study was to explore the effects of plastic film residue rate on cotton (Gossypium hirsutum L.) field water environment and root configuration under drip irrigation condition. A field experiment was established with a single factor experiment, completely randomized block design: i.e. 5 levels of plastic film residue rate 0 (A), 225 (B), 450 (C), 675 (D) and 900 kg/hm2 (E) application. The experiment was carried out in Southern Xinjiang in 2014 and 2015. In this area, the groundwater depth was 40-50 m. The soil was silt sand. The cotton variety used in this experiment was Xinluzhong 47. During the experiment, the soil water content was periodically measured. Cotton seed yield was measured. Water use efficiency was calculated based on the evaportranspiration. The cotton root diameter, length, volume and surface area were also determined. The results showed that soil moisture and root distribution were affected by plastic film residue rate. Between 80% and 95% of the root biomass was in the 0 to 30 cm soil depth, which was the area most significantly affected by plastic mulch residue for water distribution and cotton root configuration. The average water content of 0-50 cm soil gradually decreased with the increase of plastic film residue rate, and water dominant flow or water barrier benefit was generated, resulting in different degrees of water deficit appeared in each soil layer during the growth period. The average root biomass, root weight density, root length density, root surface area density, root volume and average root diameter were significantly reduced with increased of plastic film residue rate. The yield and water use efficiency were significantly decreased with the increase in plastic residual film rate. Compared to E, the root biomass of treatment A increased by 119% and 126% in 2014 and 2015, respectively, while the root weight density of A increased by 75.68% and 65.77% in 2014 and 2015, respectively. The root length density of A was 51.9% and 70.8% higher than that of E in 2014 and 2015, respectively while the average root surface area of A was 195% and 238% higher than that of E. The root volume of A was 34.62% and 60.16% higher than that of E in 2014 and 2015, respectively while the root average diameter of A was 81.3% and 84% higher than that of E. The 2-year average of the cotton seed yield and water use efficiency of treatment E was decreased by 18.50% and 13.69% compared with treatment A, respectively. Therefore, reasonable measures should be taken to remove plastic film residue and alleviate the negative influence of residual film pollution, which will be conducive to improving yield and water use efficiency in water limiting region.