Influences of Long-term Crop Cultivation and Fertilizer Management on Soil Aggregates Stability and Fertility in the Loess Plateau, Northern China

Long-term crop cultivation and fertilizer management practices are rapidly emerging techniques in the Loess Plateau, northern China. However, little is known regarding their impacts on the soil aggregate stability and how they affect soil mechanical composition and fertility. In this study, soil samples were collected from three soil depths (0-10, 10-20, and 20-30 cm) of six cultivation treatments and three fertilization treatments in the Loess Plateau. The six cultivation treatments included continuous wheat (WH), continuous maize (MA), continuous alfalfa (AL), wheat and alfalfa rotation (WAR), wheat and maize rotation (WMR), and abandoned plot (CK). Three fertilization treatments included no fertilization (CK), NP (120 kg N ha(-1) and 60 kg P2O5 ha(-1)), and NPM (additional cow dung 75 t ha(-1)). All the study field and treatments were established in 1984. In 0--20-cm layer of AL; the silt and clay particles were significantly higher than other plots. Significantly higher water-stable aggregates and root biomass were observed at 0-20 cm in AL plot also, while in 20--30-cm layer the water-stable aggregates were higher in MA, WAR, and WMR plots. With respect to the mean weight diameter (MWD), it followed the pattern of AL > MA > WMR > CK > WAR > WH for the 0--10-cm layer, AL > WAR > WMR > MA > WH > CK for the 10--20-cm layer, and WAR > WMR > MA > WH > CK > AL for the 20--30-cm layer. Similarly, to the fractal dimension (D), the treatments ranked as WH > WAR > CK > WMR > MA > AL for the 0--10-cm layer, WH > MA > CK > MAWMR > WAR > AL for the 10--20-cm layer, and WH > AL > CK > MA > WMR > WAR for the 20-30 cm, respectively. The soil organic carbon (SOC) and phosphorous (P) decreased with soil depth in all plots except WMR. The total N (TN) and phosphorous (P) observed in AL plot were significantly higher than other plots at all depths. The correlation analyses showed that TN and SOC had a positive correlation with aggregate stability, geometric mean diameter (GMD) and clay content, whilst the content of water-stable aggregates has a positive correlation with MWD and GMD. These findings suggest that long-term legume/alfalfa cultivation significantly improved aggregate stability, soil mechanical composition, and fertility.