西南喀斯特地区典型石漠化阶段土壤氮素变异研究

Variability of Soil Nitrogen in Karst Regions Under Typical Rocky Desertification Stage,Southwest China

我国西南喀斯特地区的石漠化问题已经严重制约了当地社会经济发展,揭示土壤养分变化规律对该区域生态系统适应性修复具有重要意义。以贵州省荔波县和普定县为研究区,通过野外采样和实验室分析,对西南喀斯特地区典型石漠化阶段土壤的铵态氮、硝态氮变异状况进行了研究。结果表明:(1)非石漠化的黑色石灰土中铵态氮、硝态氮的含量分别高达11.61和38.01mg·kg-1。随着石漠化程度的加深,土壤中氮素含量逐渐减少。统计表明非石漠化土壤与轻度石漠化土壤铵态氮含量呈显著差异,硝态氮含量呈极显著差异。(2)土壤铵态氮含量表现为表土层高于心土层,而硝态氮在剖面中分布规律不一致。(3)土壤氮素含量随时间有明显变化。铵态氮和硝态氮含量均在7月达到峰值,然后呈现出下降趋势,至11月或翌年1月又逐渐增加。(4)土壤有机质与铵态氮和硝态氮含量呈一元二次线性相关,相关系数分别为0.7671和0.9493,均达到极显著水平;铵态氮和硝态氮含量也呈极显著的线性相关,相关系数为0.7743。喀斯特地区通过封山育林等措施增加有机质积累可提高土壤氮素含量,对防治石漠化具有重要意义。

The karst regions of southwest China are greatly suffered from rocky desertification. The research on the variability of soil nutrient is important to the repair of local ecosystem. Soil samples were collected from Libo and Puding in Guizhou Province, and the variability of nitrogen in the soils under typical rocky desertification was studied. The results obtained were listed as follows： （ 1 ）Both ammonium（NH4^＋ -N ） and nitrate（NO3^- -N ） reached the highest contents of 11.61 mg·kg^-1 and 38.01 mg·kg^-1 in the non-degraded rendzina. As the rocky desertification progressed, the content of soil nitrogen decreased. The statistical data indicated that there was significant difference in the content of NH4^＋ -N between non-degraded rendzina and light degraded rendzina, and highly significant difference in NO3^- -N;（2）The content of NH4^＋ -N was higher in surface soil layer than in bottom layer, and NO3^ -N changed irregularly; （ 3 ）The content of nitrogen varied with time significantly. The content of NH4^＋ -N and NO3^- -N got the highest in July, then the content of nitrogen declined until November or next January; （4）The content of soil organic matter had a quadratic relation with NH4^＋ -N and NO3^- -N, and the correlation coefficient was 0.767 1 and 0.949 3 respectively, which was extremely significant. The content of NH4^＋ -N and NO3^- -N had an extremely significant relationship and the correlation coefficient was 0.774 3. It is an effective way to prevent rocky desertification by enhancing the content of soil organic matter.