Effects of residual film on maize root distribution, yield and water use efficiency in Northwest China

With the extensive use of plastic film, a large number of residual film accumulated in the farmland, bringing a huge negative impact on agricultural production. Studying the effect of residual film on roots is helpful to understand the damage mechanism of residual film on crop growth. Thus, a two-year field experiment was conducted with 0 (M0), 90 (M90), 180 (M180), 360 (M360), and 720 (M720) kg ha−1 residual film, and sine and logistic functions were used to simulate root growth and vertical distribution of maize. Results showed that root length decreased with residual film increasing and was more sensitive to residual film at tasseling, filling and maturity stages than at seedling and jointing stages. The results of the sine function fitting the total root length showed that the potential maximum root length was decreased and the rooting time was delayed, and the root growth time was shortened with the amount of residual film increasing. M90 had no significant effect on root length but residual film equal to or greater than 180 kg ha−1 had significant negative effects on root length. M180, M360 and M720 significantly reduced the actual total root length by 13.7%, 23.8% and 33.3%, and reduced the potential root length by 9.4%, 17.1% and 21.8%. M360 and M720 significantly shortened the growth time by 3.8% and 6.6%. The logistic function fit the vertical root distribution well. Residual film decreased the root length in deep soil and gathered roots in the soil layer near the depth of d50 at which 50% of the root length was accumulated. Residual film decreased the soil depth where 50% and 95% root length were accumulated and increased the proportion of root length in 0–30 cm soil layer. This adverse effect increased with residual film amount increasing. The dry matter of stems, leaves and ears decreased with residual film increasing. M90 reduced the above-ground dry matter insignificantly and the other treatments with residual film had significant effects. At the maturity stage, the above-ground dry matter in M90, M180, M360 and M720 was reduced by 2.4%, 14.2%, 22.2% and 29.4%, compared with M0. Residual film decreased evapotranspiration (ET), grain yield and water use efficiency (WUE) significantly except M90. ET, yield and WUE were reduced by 1.7%, 3.0% and 1.1% in M90, and 2.5%, 17.1% and 16.1% in M180, and 6.2%, 27.1% and 23.4% in M360, and 8.5%, 34.7% and 30.8% in M720, respectively. In summary, the residual film beyond 180 kg ha−1 had a significant negative effect on summer maize. This information will be useful to better understand and respond to residual film pollution and ensure safe agricultural production.