Effects of tillage patterns on soil moisture and soybean yield in sloping fields

Due to the differences in farming habits, geographic and climatic environment, there are great discrepancies in the cultivation methods in different rainfed agricultural areas of China. In order to study the effect of different tillage patterns on soil moisture characteristics and crop yields in sloping field of the low hilly areas in northern China. 12 standard experimental plots were set as 12 m ×5 m in the soybean fields with sloping field of 10 degree. The long sides of each plot were perpendicular to the contour lines, and the slopes were facing the same direction. In this paper, we set up four treatments: traditional tillage (CT), no-tillage (ZT), no-tillage straw mulch (NT) and Cross Ridge (CR). The bottom of each plot was equipped with a runoff pool. The vertical and horizontal variations of soil moisture content at 0-100 cm depth under different treatmentsat different growth stages of soybean were monitored. The runoff, yield and water use efficiency of soybean in different slopes were measured. The results showed that: 1) in different growth stages of soybean, the soil moisture content of each treatment in 0-40 cm was NT > ZT > CR > CT. When the soil depth exceeded 40 cm, the relationship among different treatments in soil moisture content fluctuated. Compared with the CT treatment, ZT and NT treatments could obviously increased soil moisture content by 25.34% to 35.57% in 0-50 cm. 2) The relationship between CT and ZT treatments in soil water content was slightly affected by the total rainfall during soybean growth period, which showed as follows: downhill position > midslope position > uphill position, and downhill position ≈ middle slope position > uphill position, and the relationship between NT and CR treatments in soil moisture content slightly varied with the total rainfall during the soybean growth period. 3) The spatial distribution of soil moisture in profile of each treatment showed the characters of upper wetting and down drying. The wet soil layers (volumetric moisture content ≥11.6%) in CT and CR treatment were located at 40-100 cm from the bottom of slope and 40-100 cm from the top of slope, respectively, while dry soil layers (volumetric moisture content ≤ 8.6%) were located at 10-30 cm from the top of slope and 10-20 cm from the bottom of slope, respectively. The wet soil layer (volume moisture content ≥ 12%) in ZT treatment was poorly distributed, and wet soil layer in NT treatment has centralized distribution with the largest range, occupying the 40-100 cm depth range of the whole slope. 4) The effects of three factors on soil water content were as follows: tillage pattern > depth of profile > slope position. 5) During the 2yr's experiment, compared with the CT treatment, soybean yield in CR, ZT and NT treatments increased by 8.77%, 15.68% and 26.74%, respectively, and water use efficiency increased by 6.32%, 11.6% and 20.61%, respectively. Therefore, NT cultivation mode should be preferred in soybean cultivation in the study area.