Effects of long-term chemical fertilization on soil physical properties of slope lands in the Loess Hilly Region

Based on 17 years field experiments, the effects of long-term located application of chemical fertilizer on soil physical properties were studied in cultivated slope lands in the hilly Loess Plateau of China. The results indicate that: under the condition of long-term chemical fertilization, soil physical properties in the surface layer（015 cm）do not show a trend of degradation, and those in the middle layer（1530 cm）and lower layer（3045 cm） are improved in different degrees. The influence of chemical fertilizer on soil water-stable aggregate is stronger than that on soil density or soil porosity. Soil aggregate content and aggregate stability are improved in all the three soil layers, while the soil density and soil porosity are slightly degraded in the surface and lower soil layer, but are improved in the middle layer. The long-term different levels of single-applying fertilization have no significant effect on the soil physical properties, however, the interaction of combined applying of nitrogen and phosphor is obviously higher than that of the single-applying. The rank of the effects of chemical fertilizer on soil physical properties under different fertilizer treatments is combined applying single-nitrogen single-phosphor. The N2P1 is the optimal fertilizer treatment in improving soil properties as well as sustaining soil stability in the research region.