Soil conditions in a small catchment on the Loess Plateau in China

This article presents the results from soil surveys carried out within the framework of a soil conservation research project with several components: soil erosion modelling, land evaluation and participatory planning. The study area was a small catchment (3.5 km(2)), ranging in altitude between 1085 and 1370 in, in the vast Loess Plateau area in northern China. It is continuously affected by soil erosion by water, to a certain extent due to the unprotected slopes resulting from cultivation of subsistence food by the land users. The information on variability of soil properties in the study catchment was required as a basis for development of land use scenarios opting for ecological and economical sustainable production for the land users in the future. Soil profiles to I-m depth were described, using FAO guidelines, at 17 sites along two transects covering the different facets of the morphology: hilltop, hillslope, valley bottom. Samples were collected from each horizon in the soil profiles for laboratory determination of physical and chemical properties. It was found that the nutrient status of the soils was poor, with ranges in contents of: sand=6.5-30.0%, silt=53.5-74.5%, clay=11.1-29.0%, organic matter=0.11-1.32%, available P=0.1-11 ppm, available N=5-56 ppm. The extremely high pH values, ranging between 8.7 and 9.3, effectively restricted the availability of nutrients. The soils have a high available water storage capacity so that, during years with a good supply of rain water, fair yields of crops can be achieved if the soil is fertilised. However, during dry years, when the soil dries out, the soils are vulnerable to drought and the crops fail. A divide at approximately 1200 to 1225 in above sea level was found between stratified and unstratified loessial soils. Above this altitude, the soils were yellowish, homogeneous silt loams with no or few restrictions for tillage, root penetration or water percolation. Below this altitude, layers that were more reddish (due to soil processes during climatically wetter periods),. slightly cemented or higher in clay content, although still having a silt loam texture, were found in the soil profiles. These layers could cause problems at tillage, and could give rise to some restrictions to root penetration and water percolation, thereby increasing the erosion risk. A partitioning into characteristic soil types is proposed, to be used in the other parts of the project: erosion modelling, land evaluation and participatory planning. (C) 2003 Elsevier Science B.V. All rights reserved