Effects Of Enhanced Efficiency Fertilizers And Fertilization Regime On Soil Greenhouse Gas Emission In Winter Wheat Cropping System

Enhanced efficiency fertilizers(EEFs)had been proved to have the potential to reduce greenhouse gas emissions(GHGs)and increase crop yields from cropland soils in many studies.However,the effects of different EEFs on GHGs from the semi-arid rain-fed winter wheat(Triticum aestivum)cropping systems are still unclear.Studying the effects of different nitrogen fertilizers and fertilization regime on soil GHGs is of great significance for improving nitrogen use efficiency and reducing GHGs.This study was conducted in a semi-arid rain-fed region of Southern Canada from 2014 to 2017.Two field trials were conducted to explore the effect of different nitrogen fertilizers on the GHGs from three growing seasons of winter wheat fields under the conventional fertilization regime(Trial 1)and the optimized fertilization regime(Trial 2).Trial 1 was the local farmers' common used fertilization mode(conventional fertilization regime),which including 7 treatments:no fertilizer control(Control),urea(Urea),polymer coated urea(PCU),urea ammonium nitrate(UAN),UAN+urease Inhibitor+nitrification inhibitor(UI+NI),UAN+urease inhibitor(UI),UAN+nitrification inhibitor(NI),all fertilizers were applied in two split applications:50%band base fertilizer at planting+50%broadcast in spring.Trial 2 was to optimize the conventional fertilization mode,which set up three fertilization regimes:100%banded base fertilizer at planting(100%P),30%banded base fertilizer+70%fall broadcast(30%P+70%F),30%banded base fertilizer+70%spring broadcast(30%P+70%S),4 treatments:Urea,PCU,Urea+nitrification inhibitor+urease inhibitor(Super U),Urea+urease inhibition(Urea+Instinct)and a non-fertilizer treatment(Control).The N2O,CO2,CH4 emissions,soil ammonium and nitrate,soil temperature,soil water content,and yield of winter wheat were measured in each growing season.Global warming potential(GWP)and greenhouse gas emission intensity(GHGI)were calculated to explore the characteristics of GHGs under different fertilizer treatments and fertilization regimes.The relationships between environmental factors and GHGs were assessed,and the overall effects between GHGs and GWP,yield and GHGI were evaluated.The main results are as follows:1.The application of EEFs does not always reduce N2O emissions compared to conventional nitrogen fertilizers,sometimes may increase the N2O emission,depending on the type of fertilizer and the fertilization regime.In conventional regime,except for NI,the UAN or Urea-based EEFs have the potential to reduce cumulative N2O emission and the N2O emission factors.The cumulative N2O emissions from UAN based fertilizer are higher than those from Urea based fertilizers.There was no significant difference between treatments;Except for UI+NI,the other EEFs maintained lower growing season average soil available nitrogen levels compared to UAN and Urea.Under the optimized fertilization regime,the cumulative N2O emissions were affected by the interaction of fertilizer treatments and fertilization regimes.The EEFs increased the N2O emission by 2%-10%compared to Urea,but the differences between treatments did not reach a significant level,30%P+70%F regime is not conducive to the N2O reduction;As compared to Urea,Urea+Instinct and PCU reduce soil available nitrogen content,while Super U has relatively high ammonium nitrogen content and lower nitrate nitrogen content.30%P+70%F regime or 30%P+70%S regime had lower soil available nitrogen content compared to 100%P regime.2.Under the semi-arid rain-fed conditions,fertilization showed a tendency to increase soil CO2 emissions compared to Control,which means a source of soil CO2 emission.There was no significant effect of EEFs on reducing cumulative CO2 emissions compared to conventional nitrogen fertilizers(Urea or UAN).30%P+70%S regime significantly reduced cumulative CO2 emissions by 3%-6%,compared to 100%P and 30%P+70%F regimes.3.The cumulative CH4 emission is expressed as an absorption sink,and the overall performance showed that the CH4 emission from fertilization treatment is larger than Control,indicating that fertilization treatment has the potential to reduce CH4 sink,even the difference between treatments is not significant.The fertilization regime had a significant effect on the cumulative CH4 emissions in 2014-2015 growing season.Average across the three growing seasons,the overall trend of CH4 cumulative emissions in different fertilization regimes was 30%P+70%S regime>100%P>30%P+70%F regime,indicating that 30%P+70%F regime is relatively more suitable for CH4 reduction.4.Average across the three growing seasons,canonical correlation analysis was used to test the relationship between environmental factors(climate and soil factors)and GHGs.Soil surface temperature were closely related to CO2 and N2O emissions,while soil water content was mainly affects N2O emission.Environmental factors had little effect on soil CH4 emission.In this study,the effect of soil factors on GHGs were relatively small as compared to temperature and water content.Therefore,while considering the type of fertilizer and the fertilization regimes,the impact of environmental factors on GHGs should be fully considered.5.Average across the three growing seasons,fertilizer treatments increased GWP,increased yield,and reduced GHGI as compared to Control.However,the differences between treatments varies depending on the type of fertilizer and fertilization regimes.In conventional fertilization regime,PCU showed lower potential for increasing production and lowering GWP than other fertilizers.UI were more conducive to increase yield and decrease GHGI than other fertilizers.In the optimized fertilization regime,the 30%P+70%S regime significantly reduced 6%-8%of GWP compared to other regimes.EEFs increase or decrease yield compared to Urea,depending on the fertilizer type and growing season.The yield of 30%P+70%F regime was lower than that of other regimes,indicating that the potential was poor in this regime for yield increasing.The fertilizer treatments reduced GHGI compared to Control average across the three growing seasons,and fertilizer treatments significantly reduced GHGI compared to Control in the 2016-2017 growing season.The GHGI of 30%P+70%S regime is significantly lower than other regimes,indicating a larger potential for yield increasing and GWP reduction.PCA results indicate that 30%P+70%S regime can be used as a prefered fertilizer to reduce GHGI and increase yield compared to other regimes.From the results above,we recommended 30%P+70%S regime as the preferred fertilization regime for increasing yield and reducing GHGs.In summary,regarding to the reduction of GHGs in winter wheat field in a semi-arid rain-fed conditions,different EEFs did't reach a consistent result.Considering GWP and yield in a comprehensive way,UI and Super U can be used as recommended fertilizers.However,to make reasonable strategies for actual farming management,the economic benefits that arising from fertilizer cost and farming machines and the influence of environmental factors(temperature and soil water content)on GHGs should be considered.Under the conditions of optimized fertilization regime experiment,30%base fertilizer+70%spring broadcast regime can be used as the preferred fertilization regime for increasing yield and reducing emissions.