成土母质和种植制度对土壤pH和交换性铝的影响

pH and the exchangeable aluminum content in acid soils as affected by parent materials and cropping systems

研究了我国南方 3种不同成土母质发育的酸性自然土壤的 p H与交换性铝含量状况和种植不同作物后它们的变化。研究结果表明 ,自然土壤的 p H平均值大小顺序为雷州半岛地区玄武岩发育砖红壤≤粤中花岗岩发育赤红壤 <粤北石灰岩发育红壤 ,土壤交换性铝含量的平均值的大小顺序为粤北石灰岩发育红壤 <雷州半岛地区玄武岩发育砖红壤 <粤中花岗岩发育赤红壤。种植茶树将使这 3种土壤的 p H显著降低 ,交换性铝的含量则将不同程度升高 ,最为明显的是种茶后石灰岩发育的茶园土的 p H在这 3种土壤中变为最低 ,交换性铝数量的增加幅度最大。种植水稻将提高土壤的 p H和交换性铝的含量。轮作花生后土壤的 p H也将上升 。

As a result of high annual average temperature and plentiful rainfall, acidity of soils in south China was intensive and a large number of exchangeable aluminum (Al) was accumulated in the soils. Impacts of exchangeable Al on soil properties, soil fertility, and Al toxicity to living organisms have received ample attention. Limestone fertilization has long been regarded as an effective measure to alleviate the toxicity of soluble Al to crops planted in acid soils. Acquirement of the status of pH as well as the amount of exchangeable Al in these soils was essential to resolve the problems above. This paper presented the influence of parent materials and cropping systems on the pH and exchangeable Al content in acid soils. Three types of natural soil samples, namely red soil, latosolic red soil, and latosol were collected from north Guangdong Province, its central, and Leizhou peninsula respectively, which were all representative of local soil type. Soil samples from corresponding cultivated land were also collected. As the results shown, the average pH value of these surface natural soils (0～20cm) decreased as the following sequence: 5.29 for red soil originated from limestone>4.77 for latosolic red soil originated from granite≥4.70 for latosol originated from basalt. As for the value of exchangeable Al content in the same soils, the sequence turned into 5.0 cmol/kg(1/3Al^(3+)) for red soil<20.7 cmol/kg(1/3Al^(3+)) for latosol< 45.6 cmol/kg(1/3Al^(3+)) for latosolic red soil. Both pH and exchangeable Al content in the soils, however, changed to some extent after planting crops. pH of red soil became the lowest among these three soils after planting tea though the soil was inherited from limestone with the highest pH value of natural soils. At the same time, the average exchangeable Al content in surface red soil (0～20cm) was significantly increased from 5.0 to 47.4 cmol/kg(1/3Al^(3+)), which mainly resulted from use of physiological acidic fertilizer such as KCl and (NH_4)_2SO_4 for a long period in the tea plantation. In addition, the average pH value of soils was increased after planting paddy rice, which could be attributed to the depletion of hydrogen ions (H^+) during the reduction of Fe or Mn oxides in soils by reductive substances produced during the decomposition of organic matter under flooding condition. Exchangeable Al content in these paddy soils was also larger than that of corresponding natural soils, which might result from the dissolution of Al oxides by organic acid. Finally, the average pH value of soils was increased after rotation of peanut, while the average exchangeable Al content decreased because some parts of them were exchanged by Ca^(2+) which was introduced to soils after fertilizing limestone. Then these Al were precipitated and turned to be nonexchangeable. As a conclusion, pH value and exchangeable Al content in soils were jointly determined by their parent materials and the crepping systems as well, which should be taken into account in the amelioration of acid soils.