Response Of Soil CO₂ Emissions To Water Andfertilizer Supply In Maize-wheat Farmland System

The extreme environmental problems caused by global warming in CO₂ have become the focus of attention among experts in various fields.The CO₂ produced by farmland ecosystem is susceptible affected to human activities,especially by agricultural management measures significantly,such as irrigation or fertilization.And it is the main research object of agricultural greenhouse gas emission.Therefor,there were three water levels of W1?90 mm??W0.85?76.5 mm??W0.7?63 mm?,there were four nitrogen levels of N1?300 kg·hm-2??N0.85?255 kg·hm-2??N0.7?210 kg·hm-2?and N0?0 kg·hm-2?,there were four phosphorus levels of P1?90 kg·hm-2??P0.85?76.5 kg·hm-2??P0.7?63 kg·hm-2?and P0?0 kg·hm-2?in summer maize.There were three water levels of W1?140 mm??W0.85?110 mm??W0.7?98 mm?,there were four nitrogen levels of N1?210 kg·hm-2??N0.85?178.5 kg·hm-2??N0.7?147 kg·hm-2?and N0?0 kg·hm-2?,there were four phosphorus levels ofP1?150 kg·hm-2??P0.85?127.5 kg·hm-2??P0.7?105 kg·hm-2?and P0?0 kg·hm-2?in winter wheat.The soil CO₂ emission from maize-wheat field was observed by static chamber method,to reveal the relationship between soil factors and CO₂ emission for different irrigation and fertilizer amounts.It can provide a theoretical basis for improving the quality of the environment through water and fertilizer management.The results are as follows:?1?The CO₂ fluxes of maize and wheat in the whole growth period had obvious seasonal variation,and the annual maximum appeared in the maize season,also the minimum appeared in wheat season.The main peak and the secondary peak appeared in the maize jointing period to tassel stage,the tassel period to the filling stage,other levels of emission levels were lower.The range of emission flux was 489.28-46.64 mg·?m2·h?-1.The seasonal variation of CO₂ emission in wheat season was larger,also was showed two emission peaks,the main peak appeared in the jointing stage to the grouting stage,the secondary peak appeared in the seedling stage,the lowest level was in the wintering stage.The range of emission flux was 363.64-39.23 mg·?m2·h?-1.?2?The effect of irrigation amount on soil CO₂ emission and cumulative emission in maize-wheat growth period varies with fertilization.The average CO₂ emission flux of soilduring the whole growth period of maize was as follows: under the situation of high fertilizers and low fertilizers,high water was significantly higher than that of low water?P < 0.05?,under medium and low fertilizers,no significant difference was found between water and low water?P > 0.05?.The difference between high water and low water was significant difference?P < 0.05?at high level,the difference between high water,medium water and low water was not significant in low fertilizer.?3?The effects of fertilization on the average and cumulative CO₂ flux emission of soil in maize-wheat growth period increased with the increasing of irrigation levels.The average CO₂ emission flux of soil during the whole growth period of maize was as following:In high water conditions,high fertility significantly increased by 14.82%;in medium water conditions,medium fertilizer increased by 8.03%?P < 0.05?;there was no significant difference in fertilization between low water conditions?P > 0.05?.Similarly,fertilization under high water and medium water conditions significantly increased the average CO₂ emission flux of soil during the whole growth period?P < 0.05?,under low water conditions,medium fertilizer> high fertilizer> low fertilizer,medium fertilization significantly increased than the low.?4?Nitrogen fertilizer and phosphate fertilizer resulted in a significant increasing in soil CO₂ accumulation during the whole growth period of maize,and there was a significant negative interaction between the two,resulting in significant reduce in the rate of nitrogen and phosphorus fertilizer application.The effects of nitrogen fertilizer and phosphorus fertilizer on the total CO₂ emission of winter wheat showed the identical results as that of maize,and the combination of nitrogen and phosphorus fertilizer could reduce soil CO₂ emission.There was a significant positive interaction between the 15% and 30% water and fertilizer use effects on the cumulative CO₂ emissions from maize and wheat during the whole growth period.?5?Soil temperature is the main influencing factor of soil CO₂ flux.The CO₂ fluxes of soils were negatively correlated with soil moisture?0-10 cm,10-20 cm soil layer?,and the correlation was not significant.There was a significant correlation with the content of organic carbon,but not significant.Sensitivity coefficient increases with soil depth,and the soil WFPS of maize-wheat field was decreasing.?6?The effect of water and fertilizer on the carbon balance of maize-wheat farmland ecosystem showed that irrigation,the maize-wheat farm ecosystems under different water and fertilizer treatments showed carbon sinks.The range of carbon fixation of maize cropland ecosystem was 6 257.4-6 580.8 kg·hm-2,and the range of carbon fixation in wheat farm ecosystem was 5 575.4-6 156.9 kg·hm-2,which was slightly lower than that of summer maize CNEP.Fertilization and irrigation could improve the CNEP of farmland ecosystem,and there wasno significant difference between high water and low water at high fertilizer and low fertilizer level,while that of wheat high and low water.Medium water was significantly lower than that of low.Under medium fertilizer condition of wheat,the medium water was significantly lower than that of low water?P < 0.05?.Maize and wheat under high water conditions,high and low fertility significantly not significant.The yield of maize was 4.28%,but the difference was not significant?P > 0.05?.The yield of maize was 2.71% higher than that of low fat under medium water condition,while that of wheat was 2.19%.There was no significant difference between medium and low fertilizers under low water condition,while wheat was significantly increased by 8.64% under medium water condition.When the difference of water and fertilizer content was 15%,there was obvious positive interaction with the effect of carbon fixation on maize-wheat farmland ecosystem.When the supply level was 30%,the interaction was significant to maize.?7?Compared with single application of nitrogen and phosphate fertilizer,the CNEP of farmland ecosystem increased significantly by 6.01% and 6.83%,respectively,and the interaction of nitrogen and phosphorus was significant.The nitrogen application rate was3.84%,but the difference was not significant.The interaction between nitrogen and phosphorus was not significant?P = 0.131?.