Study on soil fertility evolvement of farmland in Daxing’an rainfed farming hilly regions

Soil fertility plays an important rule in the soil resource utilization. The better understanding of both the soil fertility evolvement laws and its contributing factors is critical for agricultural conservation and management. The main aim of this study is to estimate the recent soil change in Daxing’an rainfed farming hilly regions. Data used in this study are mainly from the second national soil census conducted in 1980-1982 and the soil surveys on the concerned spot taken place in 2002-2007. Through the comparisons of soil fertility indices in years between 1982 and 2007, it is showed that total nitrogen, alkali-hydrolyzable nitrogen and readily available potassium of soil are decreased since 1982, while soil available phosphorus is increased. We find that the changing spectrums of these indices are different. The decreased organic matter content and total nitrogen content of meadow soils are larger than those in dark brown soils and black soils. The decreased alkali-hydrolyzable nitrogen content of black soils is larger than that of dark brown soils, while for meadow soils it is less than that of dark brown soils. Available phosphorus content is decreased through the years in dark brown soils, which is larger than that of black soils and meadow soils. Readily available potassium is declined in dark brown soils, which is the most among all three types of soils. According to our findings, abundant medium elements such as exchangeable calcium, exchangeable magnesium, available sulfur and available silica, and microelements, such as zinc, copper, iron and manganese remain consistently in soils of the study regions. Additionally, we find that 87.2% of the soils in the arable lands of study areas are short of boron, and 78.2% of those are in molybdenum deficiency.