The characteristics and evolution of soil nutrient in artificial black locust (Robinia pseudoacacia)forest land in the hilly Loess Plateau

In order to know the soil nutrient condition and its evolution in artificial forest land in the hilly Loess Plateau region, the soil characteristics and its temporal and spatial variation in artificial black locust (Robinia pseudoacacia) forest land with different ages were studied systematically through the approach of substituting the temporal serial with spatial serial. The result showed that the soil nutrient content of artificial forest land in the region was at the low level. The spatial variability of soil organic matter and phosphorous content was larger than that of the other nutrient in topsoil of artificial forestland. The environment factors,such as gradient, aspect and position of the slope, had effect to some extent on soil nutrient. The nutrient content of total nitrogen(TN), organic matter(OM), available nitrogen(AN), available potassium(AK) and soil nutrient index(SNI) increased with the increasing of land use years. A significant correlation was found between the nutrient content in artificial forest land and its land use years except total potassium(TK) and total phosphorus(TP). The SNI was also significantly correlated with land use years. The correlation could be simulated with the following formula: y=axb. No significant increase of OM and AN was found with the increase of land use year. However, AK increased significantly every 10years. TP and available phosphorus(AP) kept a relatively stable content in different land use years. The content of OM, TN, AN and AK and SNI increased with land use year at a rate of 0.201g/kg、0.010g/kg、0.69mg/kg、2.27mg/kg and 0.4 per year respectively in artificial forestland. In the hilly Loess Plateau region, OM, TN, AV and SNI could reach to the middling nutrient level of the region after 50years and AK could reach to the middling to up level after 30 years in artificial forestland.