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Summary In the Loess Plateau of northwestern China, a system for dry farming has evolved based on the employ of gravel mulch. A couple of lab experiments were conducted to study the influences of mulch stratum thickness and gravel grain size on water vapor flow, with a focus on resistance to evaporation in gravel mulch stratum. In Experiment 1, six treatments included mulching with gravel of different thickness (2 cm, 4 cm, 6 cm, 8 cm and 10 cm) plus no mulching (control) were studied. In Experiment 2, the 10 cm thick mulch layer consisted of different grain size gravel [2–5 (A), 5–20 (B), 20–40 (C), 40–60 (D) and 60–80 (E) mm], plus three mixture treatments. Compared to bare soil, mulched soils had significantly lower accumulated evaporation, and gravel mulch significantly increased resistance to evaporation. The aerodynamic resistance to evaporation in bare soil is higher than that in mulched treatments and the relationship between equivalent grain size and aerodynamic resistance in mulched surface can be described by a line function. The relationships between mulch resistance and mulch stratum thickness or grain size of gravel, were represented by logistic curves. The findings showed that equivalent grain size and specific surface area of gravel were sensitive indicators of mulch resistance. Based on the results of laboratory experiments, we put forward a new calculated model of mulch resistance, but further research is needed for verification and exact parameterization of this model under field conditions. [ABSTRACT FROM AUTHOR]

The use of gravel–sand mulch is a traditional water-conservation technique in the semi-arid Loess Plateau of North-western China. In this study, we investigated the 16-year effects of this mulch on soil physicochemical properties (total organic C, N and P; bulk density; Ca, Cu, Fe, Mg, Mn and Zn; soil texture; pH), microbial biomass C, N and P and enzymatic activities (peroxidase, dehydrogenase, invertase,β-glucosidase, alkaline phosphomonoesterase and urease) in a field trial in China's Gaolan County. We examined how these parameters changed after 7, 11 and 16 years of mulching. After 16 years, soil bulk density and sand content increased significantly. Soil Ca and Cu contents did not change significantly during the study period, but Fe, Mg, Mn and Zn contents all decreased significantly after 16 years. The total N increased significantly after 11 years, but total C and N both decreased dramatically and significantly after 16 years (by 22% and 13%, respectively, compared to the control). The mulch significantly increased microbial biomass C (by 29% after 11 years), with similar results for N and P, but these positive effects were lost after 16 years. Enzyme activities revealed changes in the soil microbial community over time; the mulch increased enzyme activities until 11 years, followed by a significant decrease that suggested degradation of soil quality after long-term mulching. The positive effects of the mulch (increasing soil temperature) could explain the high microbial biomass and enzyme activities after 11 years. However, long-term increases in soil bulk density and sand content (caused by mixing of the mulch layer with the surface soil) and a lack of inputs of organic matter (caused by the barrier created by the mulch layer) led to degradation of the soil after 16 years. [ABSTRACT FROM AUTHOR]

Three basic multiple-linear regression models with different sets of more readily observed environmental variables (land use, topographic and meteorological factors) were developed for the prediction of soil moisture content in space and time. The model performances were evaluated in the Danangou catchment (3.5 km2) on the Loess Plateau, China, with soil moisture content measurements. The soil moisture content measurements were performed biweekly at five depths in the soil profile (0–5, 10–15, 20–25, 40–45 and 70–75 cm) from May to October 1998 and from May to September 1999, using a Delta-T theta probe. It was indicated that the regression models could describe the relationships of soil moisture content with environmental attributes. It was found that the spatiotemporal-SM model showed the best goodness of fit since it explained the greatest fraction of soil moisture variation in both space and time, and the predicted mean, standard deviation, minimum and maximum soil moisture were closest to the observed values. This model was also either the most precise or the most economical in prediction of soil moisture content in space and time since it gives the lowest values in mean absolute error of prediction (MAE) and Akaike information criterion (AIC). There is little difference in performance and cost-benefit between the spatial-GM model and landuse-GM model. The superior robustness of the spatiotemporal-SM model over the other two models is most significant in the prediction of soil moisture content at 0–5 cm, and decreases with increasing soil depth. [Copyright &y& Elsevier]

Understanding of the characteristics of soil organic matter (SOM) and soil nutrients at the field and catchment scale is important for refining agricultural management practices and for improving sustainable land use. In order to analyze on SOM and nutrient differences among different land use types and their relationships between land use, landscape position and slope aspect, 94 sampling sites including 7 land uses were selected along 6 transects in the Danangou catchment with an area of 3.5 km2 on the Loess Plateau of China. Significant differences in SOM, total N (TN), available N (AN) and available P (AP) among these land uses were found. Higher values in SOM, TN and AN were measured in soils from woodland and grassland, but lower values in the soils from fallow land and cropland. Compare SOM and TN with cropland, intercropping land had high contents. The adjusted R2 values of regression models for SOM and nutrients with land use, landscape position and slope aspect ranged from 0.501 (SOM) to 0.134 (AP). A comparison between average predicted and measured values for SOM and each soil nutrient revealed that the predicted values in TP and AN for each land use, in SOM and TN except for fallow land and in AP except for intercropping land, shrub land and woodland, fell with in a 95% confidence interval about the measured values. The simplified predicted models of soil nutrients combined with the key value of SOM for soil quality can serve to improve agricultural practices and to provide useful information on sustainable land use. Improvement in SOM and nutrients would be expected from more C inputs including manure and crop residues and alternative cultivation practices such as developing intercropping system, building terrace for soil and water conservation, return the cropland with SOM content less than a key value of 0.44% to the grassland and woodland on the hilly areas similar to the Loess Plateau of China. At the same time, it is recommended that nitrogen fertilization addition could be decreased in the foot slope and increased on the upper slope. [Copyright &y& Elsevier]

Presents a study which examined the effects of land use and its patterns on soil moisture and nutrients in the hilly area of Loess Plateau in China. Description of the study area; Comparisons of soil moisture among land uses for wet and dry years; Effects of landscape position on soil nutrients.

Soil moisture plays a critical role in both crop growth and vegetation restoration in semiarid environments. Its spatial and temporal variability results from topography, soils, vegetation and land uses. However, little knowledge exists about the effects of land use structure on soil moisture variability. In order to analyze soil moisture variations in relation to land use patterns, five land use structures and seven land use types were selected to monitor soil moisture. Soil moisture measurements were performed biweekly at 26 locations in a small catchment on the Loess Plateau of China from May to October 1998. The measurements were taken using a Theta-Probe at five depths of soil profile (0–5, 15–20, 25–30, 45–50 and 70–75 cm). These data were analyzed for soil moisture variations in space and time for seven land use types. Three peaks and three troughs of soil moisture variations during the growing season were found. The influence of shrubland on mean soil moisture within 0–70 cm was significantly different from that of cropland, orchard and intercropping land. Three types of soil moisture changes in profile were classified as increasing, decreasing and waving types. An analysis of the differences in soil moisture for five land use structures indicated that the influences of land use patterns on soil moisture were complex. This study provides an insight into the implications for hydrological modeling, runoff and erosion control in this area. [Copyright &y& Elsevier]