黄土高原风蚀水蚀交错带沟岸对柠条林地土壤水分的影响

The most serious erosion on the Loess Plateau of China exists in the wind-water erosion crisscross region where the annual precipitation is about 400 mm, the ecological environment is very fragile, and water is the key limiting factor for improving the environment. In this study, changes of soil moisture content for Caragana korshinskii Kom. shrubland in the gully bank of the Loess Plateau were studied using the methods of soil sampling and neutron probe. A typical gully （75 m long, 28 m wide, and 10 m deep） was selected, and six neutron probe access tubes （6 m long） were installed at points 50, 100, 200, 300, 400, and 500 cm from the gully border for obtaining soil moisture data from July to October 2004 at approximately 10 d intervals. Soil samplings were simultaneously carried out for moisture determination at the six points. Results showed that the soil moisture of the shrubland in the gully bank significantly varied between 300 and 400 cm in the horizontal direction and up to 600 cm in vertical direction of the gully. Seasonal changes in soil moisture revealed a curve with a single peak that occurred at the end of August or early September. A linear regression equation was fit for soil water storage and the distance from the gully border, with coefficients depending on rainfall characteristics, sampling point, and time of measurement.

Impact of gully on soil moisture of shrubland in wind-water erosion crisscross region of the Loess Plateau

Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems.Cypermethrin and its metabolite 3-phenoxybenzoic acid (PBA) have exerted adverse biological impacts on the environment; therefore,it is critically important to develop different methods to enhance their degradation.In this study,incubation experiments were conducted using samples of an Aquic Inceptisol supplied with nitrogen (N) in the form of NH4NO3 at different levels to investigate the effect of nitrogen on the degradation of cypermethrin and PBA in soil.The results indicated that appropriate N application can promote the degradation of cypermethrin and PBA in soil.The maximum degradation rates were 80.0% for cypermethrin after 14 days of incubation in the treatment with N at a rate of 122.1 kg ha-1 and 41.0% for PBA after 60 days of incubation in the treatment with N at a rate of 182.7 kg ha-1.The corresponding rates in the treatments without nitrogen were 62.7% for cypermethrin and 27.8% for PBA.However,oversupplying N significantly reduced degradation of these compounds.Enhancement of degradation could be explained by the stimulation of microbial activity after the addition of N.In particular,dehydrogenase activities in the soil generally increased with the addition of N,except in the soil where N was applied at the highest level.The lower degradation rate measured in the treatment with an oversupply of N may be attributed to the microbial metabolism shifts induced by high N.