Effects Of Acidification And Freezing And Thawing On Release Characteristics Of Nitrous Oxide Emission In The Black Soil

With the development of society and the explosion of global population, to get more foodresources in the limited land to solve the problems, people start to produce fertilizer. Largeamounts of chemical fertilizers are applied into the soil, which can lead to serious black soildegradation. In recent years, one of the main forms of black soil degradation is soilacidification, which influences soil habitats, nitrous oxide (N2O) production process as well asemissions. The effect of alternative freezing and thawing is a non-biological effect exists in soil.It is the most common phenomenon in nature. It influences the physical, chemical andbiological characteristics of soil directly.The black soil in the north-east district of our countryexists in subhumid monsoonal climate in temperate zone. In order to determine the effect ofalternative freezing and thawing on the physiochemical and biological characteristics of blacksoil, we conducted the experiment in the the lab. The experiment mainly includes: the effect ofdifferent nitrogen applied content, water content, soil particle size, freeze-thaw frequency andmethods on N2O fluxes and denitrifying bacteria activity. The results were as follows:（1）Soil acidification would have a major impact in the black soil N2O release. N2O emissionflux in the black soil decreased with soil pH increasing. Under the same conditions of nitrogenapplied, we could find that the emission flux of N2O first increased and then decreased with theincubation increasing. Under the condition of different application rate, N2O emission fluxincreased with the amount of nitrogen applied increasing. The effect of Water content on N2Oreleased characteristics in the black soil consistent with the effect of nitrogen applied. Inaddition, under the condition of normal water content but high nitrogen applied, N2O emissionflux was higher than that of normal water content but nitrogen applied, so in soil water contentis the key factor to the N2O release flux in the black soil.In the winter, although there is no crop growth, the microorganisms in the soil is still active.Alternate freezing and thawing action makes traits and population structure of the soil microbialchanges, resulting in changes N2O emission in the soil. Overall, in the alternate freezing andthawing process N2O emission flux is lower than the soil acidification. In the alternate freezingand thawing process, N2O emission flux and denitrifying bacteria activity in the black soil wasnot affected by nitrogen fertilizer significantly, which increased with nitrogen appliedincreasing. However, they were influenced by moisture content greatly, under25%watertreatment conditions, N2O emission flux in the black soil was significantly higher than the othertwo moisture treatments. And moisture content was higher, the greater the number ofdenitrifying bacteria was, indicating activity of denitrifying bacteria is stronger, which led to themaximum N2O emission flux. In the freeze-thaw process, the effect of soil particle size on N2O release and activity of denitrifying bacteria in the black soil fluctuated in the initial stages ofcultivation, N2O flux of0.15mm diameter greater than0.5cm, but the incubation time after144h would be greater than0.15mm diameter soil. The fluctuations of denitrifying bacterianumbers are similar with N2O.With the same frequency and the same way of freezing and thawing, the results showedthat the nitrous oxide flux in the black soil would be stronger with the content increasing. Whenthe water content of15%,20%,25%, the accumulations of N2O emission flux wererespectively3250,3607and4011μg·(m2·h)-1. If we kept the soil pretreated as above and theconcentration was25%, but the frequency was different, we can find that the emission flux ofN2O first increased and then decreased with the frequency of the freezing and thawingincreasing, and a peak emission appeared at the eighth freeze-thaw cycle. However, the freezingand thawing frequency had no significant effects on the N2O emission flux. If we kept the samefrequency and the concentration was25%, but the way of freezing and thawing was different,we can concluded that slowly freezing and fast thawing was conducive to the release of nitrousoxide, and its N2O cumulative emission flux was12%larger than the fast freezing and slowlythawing. Under the above condition of freezing and thawing, the changing rule of the activity ofdenitrifying bacteria was in accordance with N2O release.