Characteristics and evolution of soil nutrients in apple orchards at the gully region of Loess Plateau

In order to know the soil nutrient condition and its evolution in apple orchards at the gully region of Loess Plateau, the soil characteristics and their temporal variations in apple orchards with different ages were studied systematically through the approach of substituting the temporal serial with spatial serial. The results show that contents of soil total phosphorus (TP), available phosphorus (AP) and available potassium (AK) are at their high levels, while contents of soil organic matter (OM), total nitrogen (TN) and available nitrogen (AN) are at their low levels. The variation coefficients of soil AP and AK are larger than those of the other soil nutrients in different orchards, and the variation coefficients of soil OM and TN are the lowest. Compared with the farmland ecosystem in the region, soil TN content is lower in the orchard ecosystem, while the other soil nutrients in the orchard are significantly higher than those in the farmland ecosystem. The contents of orchard soil nutrients are significantly different with the increase of land use years. A significant correlation is found between the soil fertility index (SFI) in apple orchards and the land use years, and the correlation could be simulated with: y =-0.0011x2+0.0419x+0.2078. In the apple orchards of the loess gully region, SFI could reach to its highest level after 19 year land using, and then decreased rapidly.