Mechanism Of Soil C、N Nutrient Losses During Wetting And Drying Processes

Under the influence of global climate change, some areas may experience frequently severewetting-drying process, or irrigation causing severe wetting-drying phenomenon after a longdrought.Alternating wetting-drying on soil C、N have an important impact on migration andtransformation.Therefore, the study was designed to study the soil C、N nutrient loss mechanismunder the wetting-drying conditions.Research conducted by the acquisition of farmland soilcultivation experiment in the room.Set up four different water conditions (wetting-drying groups,humidity groups, drought groups, flooding groups),simulation in the field of climate artificialclimate chamber experiments, the experiment mainly study the following three aspects: ToResearch the Fading regularity of the soil water and the change of soil microbial biomass undermultiple wetting-drying cycles;to research the loss of soil carbon mechanism underdrying-reweting process; to research the loss of soil nitrogen mechanism under drying-rewetingprocess.The experiments reached the following conclusions:(1) With the more experienced drying-rewetting cycles,the time of soil drought is moreshorter and water holding capacity of the soil is more waning.After a lot of drying-wettingcycles,the variation of soil moisture have a strong regularity,and can predict the situation of thewater at next cycle.Drought caused severe decline in soil bacteria,water can quickly stimulate thegrowth of bacteria.bacteria have a dramatic rangeability in the total number. fungal resistance isbetter than bacteria.A period of time after irrigation,the soil MBC content can increase rapidly.(2) The loss of mineralization of soil organic carbon can reduce in the drying period,and itcan rapidly increase after irrigation.Multiple drying-rewetting cycles maybe destroy the soilaggregate structure.It makes organic matter is exposed. The exposure of organic matter is brokendown by microorganisms at the same time.That is conducive to the outbreak of soil respiration. Indrying-reweting alternate periods of drought,the soil DOC appears slowly increase trend.Thedrying-rewetting alternate can stimulate the related enzyme activities of soil microbial,the increaseof soil enzyme activity promoted the addtion of soil carbon mineralization. (3) The process of soil nitrogen mineralization-nitrification-denitrification were changedunder drying-rewetting periods.The drying-rewetting cycles can enhance the nitrogenmineralization and increase the dissolution of nitrogen,it is advantageous to the nitrogenloss.During the early period of irrigation, the saturation of the soil water content made thepermeability of the soil air became bad.So soil denitrification process accelerated the soil nitrogenloss.The drying-rewetting cycles make the activity of urease and nitrite reductase enzymeoccurred more radical changes.In the drying-rewetting groups, the change and influence of relatedenzyme activity make soil nitrogen loss is more speed compared with other parallel groups, but itis not dramatically.(4) The Soil aggregate structure reduced the protection of the soil C and N elements in thedrying-rwetting periods.Soil aggregate was damaged after it experienced severe shrink andexpand.This damage can accumulate and make more and more soil C and N elements exposedwith the addtion of wetting-drying cycles. At the same time,Those elements were leaked from thesoil aggregate lead to the loss of their rate was accelerated.