南方典型红壤区旱地与水田土壤酸度的剖面差异性

为探明红壤区不同耕地利用类型下土壤酸度的剖面变化特征及其主要影响因素，选取江西省余江县和湖南省祁阳县的典型水田、旱地两种耕地利用类型下、第四纪红土母质发育的红壤，分5层（0-20、20-0、40-60、60-80 cm 和 80-100 cm）测定土壤pH、交换性铝、有效阳离子含量及有机质含量等指标，分析剖面酸度特征及其相互关系。结果表明：土壤pH均随土层深度的增加呈增加趋势，不同耕地利用类型下以水田剖面pH较高，范围为5.80-6.43，旱地剖面pH较低，范围为4.68-5.41。土壤交换性铝含量以水田含量较低，范围为0.16-1.56 cmol/kg，旱地的含量较高，范围为4.22-7.02 cmol/kg，水田的交换性铝含量随土层深度的增加呈降低趋势，旱地则呈现相反的变化趋势。0-20 cm土层的交换性铝与有机质含量呈显著负相关，40-100 cm土层的交换性铝与有效阳离子含量呈显著负相关。耕地利用类型是影响土壤酸度的主要因素之一，旱地土壤酸度强于水田。增加耕层土壤有机质含量可能是减缓酸化、降低交换性铝含量的原因之一。

Changes in pH at Different Depths of Red Soils Under Paddy Field and Dry Land

To investigate the changes in pH and potential influencing acidification indicators at different depths of red soil under different vegetations is significant for preventing soil acidification and improving soil quality. A series of soil samples were collected at depths of 0-20, 20-40, 40-60, 60-80 and 80-100 cm across two sites (Qiyang County of Hunan Province and Yujiang County of Jiangxi Province) from Quaternary red earth under two land use types (paddy field, dry land). Soil pH, organic matter, exchangeable base cation and exchangeable aluminum were determined, and their inner relationship was analyzed. The results show that pH of red soil profiles from Quaternary red earth is below 6.50, and increases with the increase of soil depth at 0-100 cm. Under different land use types, pH follows the order of paddy field (5.80-6.43)> dry land (4.68-5.41), the concentration of soil exchangeable aluminum follows the order of dry land (4.22-7.02) > paddy field (0.16-1.56), and it decreases with the increase of soil depth at 0-100 cm under paddy field, while dry land shows the opposite tendency. Soil exchangeable aluminum is negatively correlated with soil organic matter at 0-20 cm layer, and negatively correlated with soil exchangeable base cation at 40-100 cm layer. This study indicates that land use type is one of the important factors influencing soil acidity, and dry land has stronger acidity than paddy field. Increasing organic matter in 0-20 cm may be one of the measures to slow down acidification and reduce soil exchangeable aluminum.