SOIL ORGANIC CARBON AND NITROGEN FRACTIONS AND WATER-STABLE AGGREGATION AS AFFECTED BY CROPPING AND GRASSLAND RECLAMATION IN AN ARID SUB-ALPINE SOIL

This paper investigates effects of cropping abandonment and perennial grass growing oil soil organic C and N pools and aggregate stability, by comparing soils under native grassland. crop Cultivation. perennial grass growing and cropping abandonment, in degraded cropland at a sub-alpine site in north-western China. The pools of total and particulate organic C (115 and 37 Mg ha(-1)) in the 0-30cm soil layer of native grassland were reduced by 31 and 54% after 30 years of crop cultivation. After 4 years of conversion from cropland to perennial grass growing total and particulate organic C pools were increased by 29 and 56%, whereas 4 year cropping abandonment increased particulate organic C by 36%. Rapid increases in total and particulate N were also found in perennial grass growing and cropping abandonment soils. The native grassland soil and soils of cropping abandonment and perennial grass growing had higher carbohydrate C concentrations in the 0-10cm layer than the cropped soil. The rapid recovery of particulate organic fraction and carbohydrates in the re-vegetated soils were probably due to higher plant biomass inputs and lower organic matter decomposition compared with those in the cropped soil. Aggregate stability of the 0-30cm soil layer was significantly decreased by crop cultivation but showed a good recovery after 4 year re-vegetations. This Study suggests that reduction of soil organic matter and aggregate stability under crop cultivation may be remedied by cropping abandonment or perennial grass growing. Copyright (C) 2008 John Wiley & Sons, Ltd.