Effects of long-term continuous cropping, tillage, and fertilization on soil organic carbon and nitrogen of black soils in China

Cultivation and tillage practices alter soil properties and often lead to decline of soil quality. Adoption of appropriate agricultural management systems, however, may maintain soil productivity. This research examined the effects of long-term continuous cropping, tillage, and fertilization on soil organic carbon (C) and nitrogen (N) contents of black soils in China. Soil samples from 11-year tillage, 11-year continuous cropping, and 16-year fertilization experiments were analyzed. Soil organic carbon (SOC) and N declined with depth in all treatments. Compared with a wheat-corn-soybean rotation, continuous cropping of wheat, corn, or soybean reduced SOC and N contents, particularly SOC content. Continuous cropping of corn reduced SOC more than that of soybean or wheat in topsoil layers. Moldboard plowing significantly reduced SOC and N contents, whereas integrated tillage (i.e., moldboard plow for wheat, deep tillage (subsoiling) for soybean, and rotary tillage for corn) increased SOC and N relative to conventional tillage. Use of chemical fertilizers [N, phosphorus (P), and potassium (K)] along with return of crop residues resulted in a substantial increase in SOC and N in topsoil layers. It is proposed that the best management for maintaining soil productivity in the study area would be crop rotation along with the integrated tillage and addition of crop residues and chemical fertilizers.