黄土丘陵沟壑区不同年限苜蓿地土壤水稳性团聚体分布特征及稳定性研究

为了探索种植苜蓿对土壤质量的影响,选取黄土高原丘陵沟壑区3、7、12 a和18 a生苜蓿草地0～60 cm土层土壤为研究对象,以农田为对照(CK),采用湿筛法研究了不同种植年限苜蓿草地土壤团聚体分布特征及其稳定性。结果表明:黄土丘陵沟壑区土壤水稳性团聚体组成随着粒径减小呈阶梯式递增态势,增幅为1.22%～61.43%,以<0.25 mm的微团聚体占据优势级别,其比例达60.83%～79.72%。当农田更替为苜蓿草地后,在0～20 cm土层,随种植年限增加至12 a,土壤团聚化递增趋势明显,>2 mm、1～2 mm、0.5～1 mm和0.25～0.5 mm粒径的土壤水稳性团聚体分别为农田对照的2.03～2.75倍、1.98～2.72倍、1.31～1.65倍和1.15～1.36倍;平均重量直径(MWD)、几何平均直径(GMD)在0～20 cm土层均表现为12 a>18 a>7 a>3 a>CK,变化范围分别为0.34～0.70和0.18～0.26;分形维数(D)变化虽然较小,但在0～20 cm土层也呈现出了不同年限苜蓿草地均小于农田的规律性,变化范围为2...

Distribution characteristics and stability of water|stable soil aggregates in different alfalfa growth years in Loess Hilly|Gully Region

In order to explore the effects of alfalfa planting on soil quality, a range of different lengths of growth years (3,7,12 a, and 18 a) and a tract of farmland nearby were selected in loess hilly|gully region as objects for investigating soil aggregates size distribution in 0~60 cm soil layer. Soil samples were analyzed for fractionation of soil aggregates with wet|sieving methods. The results showed that the proportion of water|stable soil aggregates increased by 1.22%~61.43% with the decrease of particle size in studied area, and the dominant particle size was 60.83%~79.72% with micro aggregates (<0.25 mm). The topsoil (0~20 cm) in alfalfa grassland displayed a pronounced aggregation trend with the planting age to 12 a, which embodied the proportion of >2, 1~2, 0.5~1 mm, and 0.25~0.5 mm water|stable aggregates of grassland soil was 2.03~2.75 times, 1.98~2.72 times, 1.31~1.65 times, and 1.15~1.36 times of farmland soil, respectively. Both mean weight diameter (MWD) and geometric mean diameter (GMD) in 0~20 cm soil were 12 a>18 a>7 a>3 a>CK, and the variation ranges were 0.34~0.70 and 0.18~0.26, respectively. Compared with farmland,alfalfa grassland fractal dimension (D) decreased significantly in 0~20 cm soil,ranging from 2.31 to 2.43. Correlation analysis showed that the proportion of >0.25 mm water|stable aggregates (WSAP_0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) were positively correlated with soil total organic carbon (TOC). While there were no significant correlation between soil clay, CaCO₃ content and indexes of soil aggregates. Our results confirmed that organic matter was the main cementing material for soil aggregation and alfalfa plantation could promote soil aggregation and increase the stability of soil aggregates in loess hilly|gully region.