Effect Of Different Land Use On Soil Organic Carbon,Nitrogen,Phosphorus Pools In Brown Earth Profile And Microaggreagtes

To a great degree, different land use reflects authropogenic difference in land usage and intervention. Under different human intervention, basic characteristics of soil and its composition must change. This paper was conducted on the base of three land use systems (secondary forestland, tussah woodland, tilth land respectively) in the same brown earth. The distribution pattern, quantity and compositon of organic carbon, nitrogen, phosphorus in soil profile and microaggregates of surface soil were investigated through chemistry and physics analysis technology. The main purpose is provide theoretical rule and data reference for reasonably using and protecting brown earth under different human intervention. The main results were as follows:1.With the increasing degree of human intervention , namely secondary forestland change tussah woodland and tilth land, the content of different organic carbon forms (TC, LFOC, OPOC, ROC, AC) were significantly decreased in the surface soil. However, the distribution characteristic of soil organic carbon composition was different. Soil organic carbon content reduced most in surface soil, but the reduce rate of different organic carbon were decreased in undersurface layers of tilth land. This showed that soil organic carbon eluviate rate strengthen with the increasing of human intervention, soil activation layer increase thicker.2.With the increasing degree of human intervention, surface soil organic carbon decreased significantly, but the increasing of the activity of soil organic carbon in tussah woodland was more than in tilth land. This is because the proportion of Ca and Cs in total organic carbon were enhanced than secondary forest. There is no difference in average turnover time between tussah land and forest land, but less notable than tilth land, this showed that soil organic carbon stability decreased after human intervention soil.3.The content of Cr pool was decreased in great range in soil profile and microaggregates of surface soil, especially in particle size of 50～250μm reduced 75.4%, this differed from traditional viewpoint that Cr pool's stabilization is very high. This showed that Cr pool was easier to change with soil management means changing. 4. Human intervention soil occurred mainly in the soil surface, which caused the problem that various organic carbon content and distribution in soil surface microaggregates were changed greatly. The process of organic carbon loss during the land reclamation was investigated in this study, in opposition to organic carbon enter the priority to the accumulation of the small-level theory. The results showed that organic carbon content in all levels of microaggregates in soil surface significantly decreased, with the strengthening degree of Human intervention. With the damage of big microaggregate, various organic carbon components firstly were lost in big particle and then were enriched in small particle.5. From the perspective of ecology, the management of soil organic carbon Index (CPMI)in the soil profile and microaggregates significantly decreased with the increasing of human intervention. The reason is that land reclamation reduced the return of the activated carbon, non-activated carbon and total organic matter, thus reducing the quality of soil organic matter.6. Various soil organic nitrogen contents in the soil profile and microaggregates reduced after the use of the land reclamation. However, nitrogen activity in the soil surface was affected differently, which nitrogen acid slightly increased in tussah woodland under Human intervention and decreased in cultivated land. The results showed that there were different effects of land-use intensity on the effectiveness of soil organic nitrogen.7. From an environmental point of view, the increased use of nitrogen fertilizer after human intervention soil will increase nitrogen pollution risk, because nitrogen mineralization potential proportion of total nitrogen or organic matter increased in the soil profile of arable land. The results showed that nitrogen fertilizer can promote the organic nitrogen mineralization after the land reclamation, so we need to do a good job of water and soil conservation work to prevent soil erosion and runoff and even more harm to the environment.8. The total organic phosphorus in the soil surface reduced slightly and will not be affected by human intervention in lower soil surface, which differed from soil organic carbon, nitrogen components. The results showed that the extent of land use affected slightly organic phosphorus content in participation in nutrient cycling, and changed the effectiveness of organic phosphorus. 9. Human intervention will increase soil phosphorus pollution risk, because effectiveness of the organic phosphorus increased with the increase of activity and middle organic phosphorus. Above results showed that more great soil organic phosphorus can participate in the nutrient cycling after land reclamation. Along with the increasing degree of human intervention, the possibility of soil erosion and runoff increased. So the environmental hazards and the waste of phosphorus resources will not be conducive to the sustainable development of the soil.