Duan Zheng-hu

Effects of soil properties on ammonia volatilization

Abstract By using a small culture dish located above a large-sized closed dish with soil samples to trap emissions as well as applying multivariate analysis methods, the influence of soil properties on ammonia volatilization and their correlation was studied. The results showed that the ammonia volatilization rates were positively correlated with the soil pH, CaCO3, and total salt contents but negatively correlated with the organic matter content, CEC, and clay content. Of the three negative correlation factors, the CEC was most highly correlated with ammonia volatilization, while among the three positive correlation factors, the pH predominated. These results enabled to assess the magnitude of ammonia volatilization from soils. According to the correlation equation of ammonia volatilization versus pH and CEC, the potential of ammonia volatilization of some soils in China was determined and the soils were divided into four groups. It was concluded that by increasing the application rate of organic matter ammonia volatilization might decrease.

Abiotic Soil Crust Formation on Dunesin an Extremely Arid Environment: A 43-year Sequential Study

The spatial and temporal patterns of soil crust formation on stabilized dunes at Shapotou, northwestern China, were studied on a time sequence of 0, 18, 35, and 43 years. The spatial pattern of soil formation was estimated by measuring the thickness of accumulated sand fractions on the stabilized dune surface and by analyzing the particle size distribution of soil crust. The results showed that the materials forming the embryonic crusts did not come entirely from atmospheric dustfall, but more likely originated from the deflation process of shifting sand and were related to the characteristics of shifting sand particles. Irrespective of the age, all crusts contained a relatively large proportion of 0.01-0.05 mm particles, suggesting that the 0.01-0.05 mm particles provide a material basis and are a prerequisite to the formation of soil crusts. The formation of crust was a sorting and accumulation process of 0.01-0.05 mm particles. Simultaneously, the formation of stable soil crust apparently tended to be subjected to aggregation processes that include aggregation of inorganic particles themselves and aggregation of organic and inorganic particles. The soil crust was in a constantly alternating process of formation and disruption. The alternation period was about one year. Through this alternation, the fine soil layer beneath the crust can be continuously widened and thickened with increasing stabilization time.