Effects Of Soil Organic Matter On Soil Fertility And Anti-erodibility In Karst Area

In vulnerable eco-geology background of Karst area, soil degradation process is easy to occur, and unreasonable human use pattern promotes this process. Because the maintenance and increase of soil organic matter(SOM) has great effect on soil resource, the research is carried out aiming at finding out the SOM' especial meaning to vulnerable eco-geology background of Karst area , meanwhile, providing theories for the measures taken to prevent soil degradation process in Karst area.This paper chooses natural preserve region and out of preserve region in Jinfou Mountains of Chongqing in Karst area, then analyses SOM and its composition, soil fertility and anti-erosion ability. It is found out:(1) In Karst area, SOM and its component are not only affected by the environment of rich Ca, but also different in natural preserve region and out of preserve region.In Jinfou Mountains, SOM content in surface genetic soil horizon is 87.83g·kg^-1 in average, which is higher than that in zonal soil of the same latitude. The content of humic acid and fulvic acid become less with the soil depth forward, meanwhile, the lessen degree of humic acid is more than fulvic acid between the surface and subsurface genetic soil horizon. The SOM content in natural preserve region is obviously higher than that out of preserve region, and the lessen speed of SOM content along the soil depth forward is slower than that out of preserve region. Either the content of humus acid, humic acid, fulvic acid or HA/FA in the surface genetic soil horizon of soil of natural preserve region is obviously higher than that out of preserve region; meanwhile, its inner difference is smaller than that out of preserve region.(2) SOM has great effect on soil fertility of Karst area.In Karst area, SOM helps the accumulation of soil fertilities, and improves the physical condition of soil. Either total N, available N, total P, available P, available K or CEC has positive correlation to SOM. Either total K or bulk density has negative correlation to SOM. SOM has more impact on available nutrition than total nutrition. SOM in environment of rich Ca helps the soil P to gather in the surface genetic soil horizon. Humic acid has more effect on total N, available N, available P and total K, CEC and bulk density, while Fulvic acid has more effect on total P and available K.(3 ) SOM has great effect on soil anti-erodibility of Karst area.The stability of soil aggregates has close relationship with SOM. The higher the content of SOM is, the lower the destruction ratio of aggregates is. In all soil aggregates, SOM has great effect on big aggregates. The destruction ratio of big aggregates in the surface genetic soil horizon is lower than that in the subsurface, and the gap of destruction ratio between the genetic soil horizons becomes big when the content of SOM reduces. When I investigates the relationship between SOM content and destruction ratio of aggregates further, I finds that lower SOM content has little compact on destruction ratio of aggregates, while higer SOM content has more compact on destruction ratio of aggregates. Keeping higher SOM content is important to soil in Karst area which tends to be eroded. Humic acid is important to the stability of soil aggregates. In the environment of rich Ca, humic acid is very important to the stability of soil aggregates.Based on the result of the ¹³⁷Cs concentrations, we investigate that the condition of soil erosion and SOM has close relationship, which is more obvious than that in Red soil. The soil erosion rate and intensity in natural preserve region are small when SOM is more there. The soil erosion rate and intensity out of preserve region are small when SOM is less there.In a word, the researches either on soil fertility or on soil anti-erodibility come to the same conclusion: SOM has positive effect on soil and ecology in Karst Area. Unreasonable human use pattern leads to the reduction of SOM, which worsens the soil fertility and anti-erodibility in Karst Area, and aggravates the frangibility of ecology in Karst Area.