退化沙质草地开垦和封育对土壤理化性状的影响

Cultivation and Enclosure Effects on Soil Physicochemical Properties of Degraded Sandy Grassland

分析了退化沙质草地开垦耕种2年和围封恢复5年后土壤理化性状的特征和变化。结果表明:(1)开垦后2年的耕作,使0～15cm耕作层<0.1mm细颗粒组分下降了23.8%,其中0～2.5cm表层和2.5～7.5cm亚表层0.1～0.05mm的细沙损失了38.1%和27.0%,土壤的粗粒化程度已接近于流沙;土壤有机碳、全氮、全磷分别下降了38.4%,28.0%和18.4%,下降幅度随土层深度而减小。(2)围封恢复5年后,粒级分布的变化仅发生在0～2.5cm的表层土壤,极细沙(0.1～0.05mm)、粉粒(0.05～0.002mm)和粘粒(<0.002mm)含量分别提高了43.1%,11.1%和32.5%;土壤有机碳和氮磷养分的显著提高发生在0～2.5cm表层和2.5～7.5cm亚表层,7.5cm土层以下没有变化。(3)草地开垦引发了强烈的风蚀作用,使富含营养的细微颗粒吹蚀,导致有机碳和氮磷养分的损失;采取围封措施后,植被的恢复对土壤养分产生明显的截存和保护效应。

The changes of some selected physicochemical properties of degraded sandy grassland due to 2 years of cultivation and 5 years of enclosure for vegetation restoration were studied. The results were as follows: (1) Cultivation and subsequently shortterm tillage practices of sandy grassland resulted in 23.8% decrease in the proportion of fine particle size fractions (<0.1 mm) of 0~15 cm plough layer, 38.4%, 28.0% and 18.4% decrease in organic C, total N and total P compared to the adjacent grazing grassland soil due to accelerated wind erosion. The particle size distribution of 0~2.5 cm surface layer and 2.5~7.5 cm subsurface layr developed towards that of shifting sand. (2) After 5 years of enclosure, vegetation got restoration. Significant changes of particle size distribution and bulk density were observed only in the 0~2.5 cm surface layer, the proportion of very fine sand (0.1~0.05 mm), silt (0.05~0.002 mm) and clay (<0.002 mm) was increased by 43.1%, 11.1% and 32.5%, and bulk density decreased by 19.7% compared to the grazing grassland. Significant changes of the concentrations of organic C, N and P nutrients were found in 0~2.5cm and 2.5~7.5cm layer. This changes resulted from the return of great quantities of litters, and the sequestration and conservation effects of vegetation on soil organic matter and windblown fine particles. (3) The changes of characterization of particle size fractions and organic C reflected strong wind erosion in the study region, and irrational cultivation no doubt accelerated wind erosion and exacerbated soil properties. Therefore, there is a need to develop sustainable soil management and livestock grazing practices (i.e. to fence degraded grassland for rotation grazing, to stop conversion of sandy grassland, and to give up cultivation of the degraded rainfed farmland) to combat the ongoing soil degradation and desertification in the Horqin sandy land. 