Water Use Efficiency of Soybean under Water Stress in Different Eroded Soils

Soil erosion could change the effective storage of soil moisture and affected crop water use efficiency (WUE). To quantitative study differences in the WUE of soybean and the crop’s response to water stress for soils with different degrees of erosion in northeastern China, three erosion degrees—(1) lightly, (2) moderately and (3) severely—eroded black undisturbed soils and four years (from 2013 to 2016) of soybean pot experiments were used to control soil water content (100%, 80%, 60%, and 40% field capacity (FC)) and observe the crop growth processes. To study the relationships between erosion–water use–productivity, the following results were achieved: (1) the optimal water content was 80% FC for lightly eroded soil (L) and 100% FC for both moderately (M) and severely (S) eroded soil. Yield (Y) was best in M with the value of 3.12 t ha−1, which was 4.6% and 85.5% higher than L and S, respectively. Under the conditions of adequate water supply, there was no significant change in Land M, but the values were significantly different for the S ( p < 0.05). (2) Y and biomass (B) were sensitive to water stress except in the branching stage. (3) The values of WUEY and WUEB for the three eroded soils were the best at 80% FC. The stress coefficient (SF) values of the three eroded soils were not significantly different. In the flowering and pod formation stage, the SF reached the maximum under waterlogging stress. While the water shortage stress reached the maximum in the seed filling stage, the soil water content decreased by 10%, and the WUEB decreased by 15%, which was 2.5 times more powerful than the waterlogging stress. This study indicated the change in soybean growth with respect to the water response caused by soil erosion, and provided a scientific basis and data for the reasonable utilization of black soil with different erosion intensities. The results also provided important parameters for the growth of simulated crops.