Dynamics Of Soil Organic Carbon, Nutrients And Water In Different Vegetation Restoration And Land Use Types In The Semi-arid Loess Plateau Of China

To evaluate the effect of different vegetation restoration and various land use types on soil organic carbon (SOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), soil microbial biomass carbon (MBC), total N (TN), total of nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N), ammonium nitrogen (NH4-N), total P (TP), and available P (AP), soil water content and aboveground biomass, two restoring succession practices:korshinsk peashrub (a mixture of Caragana korshinskii) shrublands in an age series of 4-,10-,11-,14-and 20 yr and wasterlands occurred for 1-,3-,5-,6-and 11 yr, and four land use types were investigated:cropland, native grassland, seabuckthorn (Hippophae rhamnoides L.) shrubland (ST) and branchy tamarisk (Tamarix ramosissima) shrubland (BT). The results as shown follows:In the restoration process of abandoned lands with an age series of 1-,3-,5-, 6-and 11-yr, soil water content decreased firstly, and then increased. Soil drying was not occurred. Aboveground biomass declined with abandon years (y=-214.17x+2361.1, R2= 0.5475**,P<0.01). SOC (0-20 cm soil layer) increased with abandoned years, and it was accumulated by a rate of 1.072 Mg C ha-1 yr-1. LFOC, HFOC, MBC, TN and NH4-N improved with abandoned years. C/P was widening, and AP decreased with abandoned years. Therefore, native vegetation restoration can increase SOC, improve soil microbial activity and soil nutrients.In the restoring process of korshinsk peashrub (a mixture of Caragana korshinskii) shrubland with an age series of 4-,10-,11-,14-and 20-yr, soil water content decreased firstly and then increased. Aboveground biomass increased with growing years of shrub (y= 279.48x+1040, R2= 0.5662,P=0.001). SOC (0-20 cm soil layer) was accumulated with growing years of shrub at a rate of 0.16 Mg C ha-1 yr-1. LFOC, HFOC, MBC and TN increased with growing years of shrub. NH4-N declined with growing years of shrub. C/P was widening, and AP decreased with growing years.Four land use types were investigated and analyzed:cropland, native grassland, seabuckthorn (Hippophae rhamnoides L.) shrubland (ST) and branchy tamarisk (Tamarix ramosissima) shrubland (BT). The results show that SOC in NG, ST and BT were 13%,28% and 35% higher, respectively, than the cropland. LFOC, C/N and C/P were higher in the shrub land or native grassland than cropland. Cropland had the highest TN, NN, TP and AP due to the use of chemical fertilizers. TN, NN and AP were significantly negatively correlated with TOC and LFOC. MBC in cropland was higher than other land use types. There were significantly positive corelationship between MBC and TN, NN, AP, and significantly negative correlationship between MBC and C/N. Therefore, land use conversion from cropland to shrub land or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.