Erosion effect on the productivity of black soil in Northeast China

Continuous soil erosion has caused serious land degradation in the black soil area of Northeast China. The primary objective of this study was to determine the effects of accelerated erosion on soil productivity, as measured by soybean (Glycine max L. Merr.) yields. Eight erosion levels, 0, 10, 20, 30, 40, 50, 60, and 70 cm, were simulated by imitating the integrated process of natural erosion and tillage activity. Each erosion level had two sub-treatments: conventional fertilization and no fertilization. Soil erosion was found to affect survival probability and to cause remarkable reductions in the Leaf Area Index (LAI), plant height, pod number, biomass, and yield. Soybean yield was exponentially decreased with the increase of soil erosion depth. Compared to erosion depth of 0 cm, erosion levels of 10, 20, 30, 40, 50, 60, and 70 cm experienced reductions in soybean yield by 28.8%, 37.8%, 43.5%, 52.6%, 53.1%, 52.9%, and 64.1% respectively when fertilized whereas the reductions at those levels were 32.6%, 42.2%, 53.0%, 54.0%, 65.8%, 69.7%, and 72.6%, respectively, when unfertilized. At the erosion depths of 10, 20, 30, 40, 50, 60, and 70 cm, the yield reductions per 10 cm of soil eroded when fertilized were 28.8%, 18.9%, 14.5%, 13.2%, 10.6%, 8.8%, and 9.2%, averaged 14.9%, but when unfertilized they were 32.6%, 21.1%, 17.7%, 13.5%, 13.2%, 11.6%, and 10.4%, averaged 17.1%. The results also showed that chemical fertilizers could enhance the yields of eroded soil, but could not recover the yields to the pre-erosion level. Additionally, the results indicated that the primary reason for the decrease in soybean yield with increasing erosion depth was the loss of soil organic matter, soil N and P. These results may aid in selecting effective soil erosion control strategy, forecasting land degradation, establishing soil erosion tolerance, and evaluating the economic cost of soil erosion in the black soil region in Northeast China.