丘陵区耕地土壤剖面有机质含量分布特征及其影响因素分析

为了进一步了解耕地有机质剖面信息，基于325个剖面（0~60 cm）采样数据，运用经典统计学探讨了重庆市耕地有机质剖面分布特征，并通过多因素方差分析对比了成土母质、土地类型、海拔对土壤有机质剖面分布的影响。结果表明：（1）基于成土母质、土地类型、海拔的CART树模型对0~20、20~40、40~60 cm土层有机质变异解释率分别为57%、44%、35%。（2）土壤有机质随土壤深度增加而减少，表现出较强的表聚性，0~20 cm土壤有机质均值是20~40 cm的1.5倍，是40~60 cm的2倍。（3）成土母质、土地类型、海拔均对0~20 cm土壤有机质含量变化产生显著影响，海拔对20~40 cm土壤有机质含量变化产生显著影响，成土母质对40~60 cm土壤有机质含量变化产生显著影响。（4）海拔和成土母质的交互作用对不同深度土壤有机质变化均产生显著影响，冲积母质、石灰岩母质发育的土壤在500~1 000 m的海拔区间上有机质含量最高，紫色母质发育的土壤有机质含量与海拔呈正相关关系。

Distribution Characteristics and Influence Factors of Organic Matter Content in Cultivated Soil in Different Horizons in Hilly Areas

A total of 325 samples collected from cultivated land profiles were analyzed to investigate the factors affecting soil organic matter (SOM) variability in different horizons (0-20 cm, 20-40 cm, and 40-60 cm). Factors including parent materials, land types, and elevation were examined by classical statistics and classification and regression trees (CART). The results showed that the CART models could explain 57%, 44%, and 35% variability of SOM in 0-20 cm, 20-40 cm, and 40-60 cm, respectively. SOM decreased with the increase of soil depth. More specifically, the mean value of SOM in the 0-20 cm soil horizon was 1.5 times higher than that in the 20-40 cm, and 2 times higher than that in the 40-60 cm. The factors affecting SOM variability differed with soil horizons. The most important parameters were parent material, land type, and elevation for 0-20 cm. Elevation was the critical variable for 20-40 cm and parent material was the key one for 40-60 cm. The interaction between elevation and parent material had a significant effect on the variation of SOM in different horizons. Soils developed from alluvial and limestone parent material had higher values of SOM content at an elevation range of 500-1 000 m. Elevation was positively significantly correlated with SOM in soils developed from purple parent material.