The effects of land use and its patterns on soil properties in a small catchment of the Loess Plateau

Due to relatively strong human activities in the hilly area of Loess Plateau, the natural vegetation has been destroyed, and landscape pattern based on agricultural land matrix was land use mosaic composing of shrub land, grassland, woodland and orchard. This pattern has an important effect on soil moisture and soil nutrients. The Danangou catchment, a typical small catchment, was selected to study the effects of land use and its patterns on soil moisture and nutrients in this paper. The results are as follows: The comparisons of soil moisture among seven land uses for wet year and dry year were performed: (1) the average of soil moisture content for whole catchment was 12.11% in wet year, while it was 9.37% in dry year; (2) soil moisture among seven land uses was significantly different in dry year, but not in wet year; (3) from wet year to dry year, the profile type of soil moisture changed from decreasing type to fluctuation-type and from fluctuant type to increasing type; (4) the increasing trend in soil moisture from the top to foot of hillslope occurred in simple land use along slope, while complicated distribution of soil moisture was observed in multiple land uses along slope. The relationships between soil nutrients and land uses and landscape positions were analysed: (1) five nutrient contents of soil organic matter (SOM), total N (TN), available N (AN), total P (TP) and available P (AP) in hilly area were lower than that in other areas. SOM content was less than 1%, TN content less than 0.07%, and TP content between 0.05% and 0.06%; (2) SOM and TN contents in woodland, shrub land and grassland were significantly higher than that in fallow land and cropland, and higher level in soil fertility was found in crop-fruit intercropping land among croplands; (3) soil nutrient distribution and responses to landscape positions were variable depending on slope and the location of land use types.

Hydrological cycle research by D&^(18)O tracing in small watershed in the loess hilly region

The objective of this study was to determine the mechanisms of the hydrologic cycle in the loess area in China.Sixty eight water samples from precipitation,soil water of the 0-4 m layer,surface water in the valley,ground water(spring and well)were collected and the Deuterium(D)and Oxygen-18(^(18)O)of these water samples were analyzed to interpret the relationship among those waters in the watershed in the loess hilly region during 2005-2009.The results show that:the D&^(18)O of precipitation in Yangou was consistent with that of Xi,an,apparently the north migration of water vapor in Xi^an;according to the correlations among the differential waters in D&^(18)O,confirmed that precipitation recharge could account for most of the sources of valley flow,with part of the recharge water going to soil water recharge.The D&^(18)O of groundwater were very close to that of precipitation,likely the soil preferential flow was dominant in groundwater recharge although the infiltration had a certain lag.Under the influence of rainfall and evaporation,the response of the soil moisture profile,and its D&^(18)O profile were different.The soil moisture had the strong influenced layer in the 60-160 cm range,a weak impacted layer in 60 l60 cm,and a stable layer below l60 cm.It was shown that the soil evaporation depth could be up to l60 cm because the D&^(18)O changed in that depth.The study could increase our understanding of the magnitude and pattern of the hydrologic cycle,which should improve water resources management in the watershed scale.