半干旱典型草原区退耕地土壤结构特征及其对入渗的影响

坡地土壤降雨入渗、径流和侵蚀过程与土壤结构密切相关.试验样地为宁夏固原云雾山自然保护区的坡耕地、退耕6a、退耕11 a(前8 a放牧,后3 a禁牧)和退耕16 a坡地,室内测定土壤结构指标,野外采用基于径流-入流-产流方法的新型降阿仪器在17、43和56 mm/h雨强下观测坡地土壤的入渗性能,分析土壤结构特征对入渗的影响.对土壤结构的稳定性指标、孔隙性指标和分形维数指标进行分析,结果表明,随着退耕年限的延长,土壤团聚体稳定性增强,土壤结构孔隙状况得到明显改善.模拟降雨结果显示,随着雨强的增大,退耕地的土壤入渗率增加,但坡耕地反而降低.退耕11 a样地受放牧牲畜践踏影响,入渗性能最差.通过逐步同归分析可知,在17 mn/h和56 mm/h阿强下,影响土壤稳定入渗率的土壤结构因子主要是容重和有机碳含量,而在43 mm/h雨强下主要是毛管孔隙度和非毛管孔隙度.土壤有机碳含量和孔隙状况的差异致使土壤结构特征不同,从而对入渗性能和过程产生明显的影响.

Soil structural characteristics and its effect on infiltration on abandoned lands in semi-arid typical grassland areas

Soil rainfall infiltration, runoff and erosion are closely correlated with soil structure. Based on a new simulated rainfall method (run off-on-out method) and apparatus soil infiltration on abandoned slope lands of Yunwu Mountain in Guyuan of Ningxia were measured. The experiments were operated on slope farmland, 6 years, 11 years (graze 8 years and enclose 3 years) and 16 years abandoned lands under 17 mm/h, 43 mm/h, 56 mm/h rainfall intensities. Soil structural indices were determined in laboratory and evaluated the effects of soil structural characteristics on infiltration capability. Soil structural stability indices, pore indices and fractal indices indicated that as the years of abandoned lands increased, soil aggregate stability and porosity were significantly increased. With increasing simulated rainfall intensity, soil infiltration rates under abandoned lands increased while decreased under slope farmland. Top layer of 11 years abandoned land tightened by grazing had poor infiltration capability. By step-regression analysis soil steady infiltration rates under 17 mm/h and 56 mm/h rain intensities were mainly effected by bulk density and soil organic carbon content, and by capillary porosity under 43 mm/h rain intensity. Overall, the results indicated that soil structural characteristics controlled by soil organic carbon contents and pore characteristics largely influenced soil infiltration capability and processes.