湿润速度和累积降雨对土壤表面结皮发育的影响

土壤表面强度和微结构显微照片是研究表土结皮的重要指标和直接表征。以两种典型的土壤(垆土和黑土)为研究对象,采用2mmh-1(慢速)和50mmh-1(快速)两种速度湿润后进行雨强为60mmh-1的降雨,研究不同湿润速度和累积降雨对结皮发育的影响。结果表明:湿润速度对垆土结皮发育过程的影响不明显,土壤表面强度主要由累积降雨打击夯实引起;快速湿润对黑土结皮发育有显著的影响,慢速湿润后黑土在60min降雨过程中没有明显的结皮,累积降雨的打击起次要作用;湿润速度和累积降雨的对结皮发育的影响取决于土壤团聚体稳定性。

Effects of wetting rate and cumulative rainfall on crust formation

Surface seals and crusts, formed as a result of aggregate disintegration and compaction during a rain or irrigation event, are higher in shear strengths, greater in bulk density, finer in pore and lower in infiltration rate than the underlying soil. Soil surface strength and micromorphological photos are important indices and direct representations in the research on soil crust. Two soils, Lu Soil and Black Soil, typical of arable soils in China, were used to investigate effects of wetting rates (WR) of (2 (low) or 50 (high) mm h~(-1)) and cumulative rainfall on crust formation, under simulated rainfall with intensity of 60 mm h~(-1). The experiment indicated that the effect of WR was negligible, but that of cumulative rainfall was significant on crust formation of Lu Soil. The crust formation processes of Black Soil were affected mostly by WRs. High WR had much greater effect than the low WR. Disintegration of soil aggregates plus rainfall of high intensity led to formation of crusts of high surface strength. Thus, the relative importance of WR and rain depth depends on stability of soil aggregates. For soils with stable aggregates, the impact of raindrops impact alone is not sufficient to destroy aggregates and form crusts. Fast wetting of dry soil is essential for aggregate breakdown and crust formation. For soils with unstable aggregates, the impact of raindrops is sufficient for seal formation.