Effects of tillage methods and straw mulching on the root distribution and yield of summer maize

Abstract: To explore root distribution and water-use efficiency of summer maize based on different tillage depth and straw mulching, a field experiment with different tillage mode was conducted in the Hetao Irrigation district in 2017 and 2018, respectively. The experiment consisted of 4 different tillage modes. It included conventional tillage mode (CK), straw mulching tillage mode (BF), deep ploughing and straw deep-buried tillage mode (SM), deep ploughing and straw mulching and deep-buried tillage mode (BFSM). The results showed that there was significant that BF treatment increased the horizontal root length density. Compared with CK treatment, the straw mulching tillage mode significantly increased by 24.7% (P<0.05). It was beneficial to the horizontal root growth, but it led to the redundancy of the surface root system. Meanwhile, there was no significant effect on the root length density of the deep root system, and it was not conducive to the growth of the deep root system under the straw mulching tillage mode. It was significant that SM and BFSM treatments increased the root length density of deep soil and they promoted the vertical growth of roots. Compared with CK treatment, the straw deep-buried tillage mode significantly increased by 23.8% (P<0.05), but it was no significant effect on the root length density of surface soil roots. The root length density of BF treatment was only 0.85% higher than CK treatment in the straw inter-layer, which was no significant difference (P<0.05). However, the root length density of SM and BFSM treatments of the straw inter-layer was much higher than BF and CK treatments. The average root length density of BFSM treatment was 3.5% higher than SM treatment, which was no significant difference (P<0.05). It indicated that it could significantly improve the root length density of straw inter-layer and promote the growth of deep root under deep ploughing and straw deep-buried tillage mode. It showed a significant third-order polynomial function relation between root length density of summer maize and normalized root depth of soil under different treatments of 2017. The model was calibrated with the measured data of 2018, which showed good calibration effect. And the Coefficient of Determination (R2) was above 0.96 between the simulated value and the measured value, and the Root Meant Square Error (RMSE) was between 0.1 and 0.2. So, it was well to describe the distribution of root length density of summer maize under different tillage modes. Compared with CK treatment, the mean of the dry root weight and the root-shoot ratio of BF, SM, and BFSM increased by 14.2%, 32.8%, 36.6%, and 3.8%, 20.8%, 26.4% (P<0.05), respectively. There was no difference in dry root weight and the root-shoot ratio of SM and BFSM treatments in the same year, but SM treatment in rainy years (in 2018) significantly increased by 6.5% on average (P<0.05) of root-shoot ratio compared with less rainy years (in 2017). Compared with CK treatment, the yield of summer maize under BF, SM, and BFSM treatments increased by 8.6%, 19.5%, and 19.7%, and water-use efficiency of summer maize increased by 13.6%, 32.3%, and 34.8% on average (P<0.05). There was no significant difference between SM and BFSM of yield and water-use efficiency, but the difference was significantly higher than that of BF and CK treatments in rainy years (in 2018). The indicators of production increased to different degrees, but the water consumption in agriculture was incremental and the water-use efficiency under 4 treatments was decreased by 9.1%, 9.1%, 6.5%, and 4.9%, respectively. The research preliminarily revealed a response mechanism which was the effect of different depths of the straw returned and tilling on the root distribution, yield, and water-use efficiency of summer maize in the Hetao irrigation district. It could achieve the goal that was saved water and stable yield based on the deep ploughing combined with straw deep-buried tillage mode, which had certain theoretical and practical significance for suitable tillage mode for agricultural production in the Hetao irrigation district.