Soil nutrients in relation to land use and landscape position in the semi-arid small catchment on the loess plateau in China

Characterizing spatial variability of soil nutrients in relation to site pr operties, including climate, land use, landscape position and other variabl es, is important for understanding how ecosystems work and assessing the ef fects of future land use change on soil nutrients. In order to assess the e ffects of land use and landscape position on soil nutrients consisting of s oil organic matter (SOM), total N (TN), total P (TP), available N (AN) and available P (AP), soil samples were collected in August and October 1998 an d July 1999 from three transects in a small catchment on the loess plateau, China. The three transects consisted of typical land use structure from th e top to foot of hillslope in the study area: fallow land - cropland - wood land - orchard (Tl), fallow land - shrub land - fallow land - cropland - wo odland - orchard (T2) and intercropping land - woodland (T3). Significant d ifferences among land uses were found for SOM, TN and AN. Woodland, shrub l and and grassland had the higher levels for them compared to fallow land an d cropland. Use of soil deterioration index showed that soils deteriorated moderately ( - 17.05%) under orchard and seriously (ranging from -29.91% to -20.32%) under fallow land, cropland and intercropping land, while soils h ad no deterioration ( - 0.74%) under shrubland and ( - 0.69%) grassland. Th is study indicated that the cultivated hilly lands must be abandoned before a critical minimum SOM of 0.492%. Soil nutrient responses to landscape pos itions were variable depending on transect and the location of land use typ es. The highest levels in SOM, TN and AN were observed at middle slope posi tion on T1, while they occurred at foot slope position on T3. However, an i ncreasing trend from upper slope to foot slope for five nutrients were foun d on T2. (C) 2001 Academic Press.