Dynamic changes of soil nutrient and enzyme activities under accelerated soil erosion conditions caused by deforestation during the past 100 years

Taking croplands located at sunny hillslopes with different years of deforestation as a case study, dynamic changes of soil nutrient and soil enzyme activities following 100 years of deforestation were analyzed. Results showed that after 100 years of deforestation, soil organic C, total N, alkaline phosphates and invertase activities obviously decreased in both 0-20 cm and 20-40 cm layers of soil profile as deforested years increased. Compared with corresponding forestlands, soil organic C, total N, alkaline phosphates and invertase activities in 0-20 cm layer of soil profile reduced by 26.6%-84.4%,17.6%-76.9%, 15.7%～73.8% and 37.6%-68.6%, respectively; soil organic C, total N, alkaline phosphates and invertase activities in 20–40 cm layer of soil profile reduced by 30.7%-81.0%, 8.3%-71.9%, 17.3%-96.9% and 51.1%-92.6%, respectively. The reduction rates of soil organic C, total N, alkaline phosphates and invertase activities in the earlier years of deforestation were greater than those in the late years of deforestation. Meanwhile, the differences of soil organic C and total N between 0-20 cm and 20-40 cm of soil profile became less and less as deforested year increased. Soil urease activities increased in the earlier years of deforestation, then decreased in the later years of deforestation as deforested year increased. Soil urease activities were highest in the 9th year of deforestation. Due to P fertilizer application rates in top soil, change trend of soil available P in 0-20 cm layer of soil profile was fluctuant; but soil available P in 20-40 cm layer of soil profile decreased slightly with deforested years.