Effects Of Different Reclamation Activities On Soil Nitrogen Dynamics

Soil nitrogen is an important nutrient element for plant growth.Different land use types have different effects on soil nitrogen dynamics.In recent years,the reclamation of coastal wetlands has been widely used as an important countermeasure to cope with the shortage of land resources.More and more researchers have paid attention to it,but the influence of different types of reclamation on soil nitrogen elements caused by reclamation is less.By comparing the six kinds of land types(reed marshes,farmland,salt fields,fish ponds,town construction and light shoal)in YanCheng reclamation area,this paper explores the effects of different types of reclamation land use on soil mineralized nitrogen and soil organic carbon and nitrogen and the effects of different reclamation years on soil nitrogen mineralization,to provide theoretical reference for the effective management of coastal reclamation activities and the rational utilization of coastal wetland.The results showed that:(1)The total nitrogen content in the soil layer of the fish pond is much higher than that of the other types,which is due to the retention of the nutrient elements in the fish pond and the increase of the effective source of the nitrogen elements in the soil.The ammonium nitrogen content of farmland and fish pond land use type decreased in the depth of soil,which was closely related to the farmers' fertilization and fishery culture in fish ponds,which made the release rate of ammonium nitrogen expedited;the soil ammonium nitrogen content in the salt field and the shoal type increased in each soil depth.related to frequent flooding and not loosened of soil.The increase of nitrate nitrogen content in the soil of the fish pond is significantly higher than other land use types,it is because the aquaculture activities in the fish pond make the organic matter content in the sediment high,which greatly improves the heterotrophic nitrification rate in the fish pond.The nitrogen mineralization rate of different land use types decreases with the increase of soil depth,which is due to the increase of soil depth,the rapid decrease of the number of microorganisms,the gradual decrease of soil permeability,and the less and less organic matter for degradation.(2)In the different land use types,fish pond has the largest soil organic carbon and nitrogen reserves,water soluble organic carbon content,microbial biomass carbon content,mineralized carbon content.It may be due to the long-term water flooding causing the anaerobic environment to increase soil carbon and nitrogen accumulation.At the same time,fish ponds have long been put into fodder and other organic substances,fish and other animal residues in fish ponds or a large amount of animal emissions are deposited in the mud,which greatly increases the soil organic carbon and nitrogen reserves.(3)The total soil nitrogen content of the same land use type formed by different reclamation time is different,but the difference is not significant.This may be because our sampling site is farmland,and the frequent farming activities of farmers have a great influence on the soil nitrogen content.The different reclamation time had no significant effect on the nitrogen mineralization rate in the wheat soil but had a significant effect on the nitrogen mineralization rate in the rape soil.The soil nitrogen mineralization rate of 16-year soil reclamation time was lower than that of 9-year reclamation time.The aboveground plant is partly harvested by farmers,and the longer the reclamation time,the less organic matter available in the soil,so the rate of nitrogen mineralization is lower.(4)The study shows that different reclamation types have great influence on soil mineralized nitrogen and soil organic carbon and nitrogen,and the different years of reclamation have different effects on soil mineralized nitrogen.In the subsequent reclamation of coastal wetlands,we should pay attention to the influence of these factors on the wetland,study the change of nitrogen elements in the soil regularly,formulate appropriate reclamation strategies,and better protect the ecological environment.