Study On Soil Nitrogen Form's Distribution And Loss Law In Karst Area

The karst area of southwest in China is very vulnerable on ecosystem.Because of the special geological condition, physical geographic background and irrational human activity, the human was driven to the poverty of a vicious circle in the end with destruction of ground vegetation, soil erosion and degradation then a large area rock desertification. The soil in karst area is an important part in ecosystem with its particularity. And the soil nutrient is an important indicator to measure the soil quality. Nitrogen is a dominating nutrient in soil released by the Soil organic matter with the action of microorganisms. So study on soil nitrogen in karst area is extremely important. This paper tried to study the soil nitrogen form's distribution and loss law on the top of Mt.Jinfo,Karst area,Chongqing. And it can help to find the effective fertility and loss status. Also we can estimate the way of soil nutrients loss in karst area according to nitrogen form loss law and speculate variety of factors affecting to the nutrient loss.And then provide a reference for nitrogen management in processes of rocky desertification prevention, ecological restoration and reconstruction.In this study,taking the top of Mt.Jinfo of Chongqing as an example,we select nine types with different height and much the same vegetation form. According to pedogenetic layer of soil collected 25 soil samples. Also we select six land-use types (including hippodrome land, grassland, azalea land, bamboo forest etc.).According to pedogenetic layer of soil collected 17 soil samples. In laboratory carry out the basic physical and chemical properties analysis, Soil moisture analysis, soil bulk density analysis, soil total nitrogen analysis, soil Inorganic Nitrogen analysis and the elements in the soil like K,Na,Ca,Mg etc.full volume analysis. The results show that:1.The analysis of total nitrogen of soil on the top of Mt.Jinfo Slope indicates that the average content of soil nitrogen is 4.42g/kg. The soil total nitrogen content has a trend of decrease with height reduction.It Shows that the nitrogen nutrient in study area not as non-karst areas as the phenomenon of accumulation at the bottom of slope.2.The analysis of soil nitrate and ammonium nitrogen indicates that the nitrate is not consistent with the general laws that on the same soil profile the Soil nutrient content decrease with the depth of deeper. View of the whole slope, the content of nitrate has a trend of decrease with height reduction in September. In March.it is not obvious. It is speculated that nitrate underground leakage is very possible. Soil ammonium nitrogen meet the general characteristics on the same soil profile the Soil nutrient contents decrease with the depth of deeper. Nitrate in March were significantly less than it is in September. But ammonia nitrogen content is opposite with the former. Soil ammonia nitrogen content is as the same as the content of nitrate characteristics on the whole slope.(except for a small number of individual samples). It is different from the previous research results that ammonium nitrogen is a major existing form of inorganic nitrogen in the soil in this study area.3.The analysis of soil organic matter, available nitrogen, pH etc. indicates that the average content of organic matter is 96.14g/kg in this area. The total nitrogen content has strongly positive correction with organic matter content. But C/N values in the study area are rising with the height reduction. In other words, with the slope height reduction the relative nitrogen content in soil decreased. It is speculated that the relative reduction of nitrogen has a relationship with the leakage of some nitrogen form. Also the organic matter in the soil has positive correction with vegetation coverage usually. The available nitrogen of soil has no significant relationship with organic matter. The pH in study area is lower than other karst area. The maximum value is 5.14, the lowest value is 3.67 and the average is 4.52.The moisture content of soil in this area is relatively high, the minimum value is 41.12% and the maximum value reached 118.18%.But it has no obvious direct relation between the moisture and nitrate and ammonium nitrogen.4. The analysis of other nutrients of soil indicates that the total phosphorus content has the same trend to total nitrogen content in the whole slope. Through analyzed on soil nutritive elements, like that K,Na,Ca,Mg,Fe,Mn,Cu,Zn,Mo, we can find that these four elements (Fe,Mn,Cu,Mo included) gradually reduced from the top of the slope to the foot.But the result is opposite with Mg element And these six elements(K,Na,Mg,Fe,Mn,Zn,Mo included) show the law of Ashrub land>bamboo forest>grassland>azalea land>hippodrome land. Nitrate and ammonium nitrogen content changed only a little in the whole year. In this study, we also find that ammonium nitrogen is a major existing form of inorganic nitrogen in the soil. Human activities lead to change the soil particle size,also lead to change soil nutrients and soil particle size is also relevant to underground leak of nitrate in karst soil.