粤北岩溶区不同土地利用方式对土壤钙离子的影响

Impact of Different Land Use Types on Soil Calcium in Northern Guangdong

在广东省英德市九龙镇峰林平原选择峰林坡麓灌丛、积水洼地、砂糖橘林、竹林、菜地、稻田6种不同土地利用类型,采集不同土地利用方式下不同深度的土壤,利用原子吸收分光光度计测定了土壤全钙、交换态钙和水溶性钙质量分数,结果表明:1)菜地、稻田、砂糖橘林和竹林土壤厚度显著大于自然坡麓和积水洼地;2)岩溶积水环境中(积水洼地和稻田)土壤全钙质量分数平均超过59 g/kg;其次为坡麓土壤,平均为20.83 g/kg;人工耕作的砂糖橘林和菜地土壤全钙质量分数分别降低至3.51和2.76 g/kg,而相邻的非岩溶区土壤的全钙质量分数仅为1.43 g/kg;3)耕地施肥会增加土壤的交换态钙和水溶性钙质量分数,菜地和砂糖橘林土壤交换态钙离子、水溶性钙占全钙的比例分别为38.04%、23.08%和1.41%、0.88%,而积水洼地和坡麓灌丛只有7.86%、6.87%和0.25%、0.46%。由于菜地和砂糖橘林的全钙质量分数降低,而交换态钙和水溶性钙质量分数增加会进一步加剧钙元素流失;4)不同土地利用类型土壤全钙、交换态钙和水溶性钙质量分数随深度变化呈波状下降趋势,积水洼地与稻田钙随深度的变化远比菜地、砂糖橘林和竹林剧烈;5)土壤厚度、岩石裸露率、坡度相互呈显著负相关,土壤全钙、交换态钙、水溶性钙之间均呈显著正相关,岩石裸露率与交换态钙呈显著负相关,水、土壤厚度、岩石裸露率与坡度共同决定了土壤钙的分布和迁移。

In theKarstpeak forest-plain area of Jiulong Town inYingde,Guangdong,six land use types,namely slope shrubs,water depressions,sugar-orange forests,bamboo groves,vegetable patches and rice fields,were selected to be studied, theirsoilatdifferent depth weresampled, and thenthe total calcium content, the exchangeable calcium content,and the water soluble calcium content weremeasuredby atomic absorption spectrophotometer. The results showed that： 1）The thickness of the soils invegetable patches,rice fields, sugar-orange forests and bamboo groveswere significantlygreaterthanthat ofnatural slope shrubs and water depressions;2）The total calcium content of soilin Karst water environment（water depressions,rice fields）was over 59g/kgon average, which wasthe highest among the six land use types,the secondwasthat of thesoil on slope,which was20.83g/kg. In the cultivated environment of sugar-orange forests and vegetable patches,the total calcium content reduced to 3.51 and 2.76 g/kg, respectively.Bycontrast,inthe adjacent non-karst regions, total calcium contentof soil was only 1.43g/kg. 3）Because cultivating and fertilizing would increase the exchangeable calcium content and the water soluble calcium of soil,the proportion of exchangeable calcium and water soluble calciuminthe total calciumcontent were, respectively, 38.04%,23.08%forvegetable patches, 1.41%,0.88%forsugar-orange forests,7.86%,6.87%forwater depressions, and 0.25%,0.46%forslope shrubs. Since the total calciumwas reducing in vegetable patches and sugar-orange forests,the increase of exchangeable calcium and water soluble calcium would aggravate the calcium loss. 4）The variationsoftotal calcium, exchangeablecalcium and soluble calcium contents with soil depth showed adecreasingtrend under different land use types,however,thevariationsin water depression and rice fieldswere much greater than those invegetable patches,sugar-orange forests and bamboo groves. 5）The thickness of soil,bare ratioofrock and slopewere significantly negatively correlated witheach other,while a marked positive correlationexisted amongtotal calcium,exchangeable calcium and water soluble calciumin soil,and also a significant negative correlation existed betweenbare ratioof rockand exchangeable calcium. In conclusion,water,soil thickness,bare ratioof rockand slope jointly determined the distribution and migration of soil calcium.