| Hetao irrigation area is one of the important production bases of commodity grain in China.Due to the large salt content of soil parent material and the influence of climate,unreasonable irrigation and drainage conditions,agricultural measures and artificial unreasonable fertilization for a long time,the problem of soil salinization and secondary salinization is prominent,which seriously restricts the sustainable development of agriculture.In addition,farmland is an important source of greenhouse gas emissions.Therefore,it is of great significance to carry out the mechanism and technology research on the transformation of saline alkali land into soil and fertilizer,the increase of production and the reduction of greenhouse gas emission.In this study,based on the achievements at home and abroad,combined with the actual situation of the study,we proposed that biochar(DC,22.5 t/hm2),straw returning to the field(DJ,20.625 t/hm2),straw deep burying(DJM,12 t/hm2),desulfurized gypsum(DS,37.5t/hm2)and desulfurized gypsum plus organic fertilizer(DSF,37.5t/hm2each)should be applied in salinized soil In 2017-2019,a three-year field plot experiment was carried out to study the effects of long-term application of different improvement measures on the medium and heavy salinized soil improvement,carbon sequestration and emission reduction,and the growth of sunflower,in order to comprehensively analyze and select the improvement measures for improving soil fertility,sunflower yield and carbon sequestration and emission reduction,so as to provide comprehensive treatment for salinized soil in Hetao irrigation area Theoretical basis.The main conclusions are as follows:(1)Different improvement measures can reduce soil bulk density,increase soil porosity and field water holding capacity,among which biochar treatment is the best.The soil temperature of 5-25cm soil layer can be increased steadily by each improvement measure,which can promote seed germination and sunflower growth.In the three years.The application of improvement measures can improve soil nutrients,promote the transformation of NH4+-N to NO3--N,and improve the utilization rate of soil nitrogen,especially the effect of desulfurization gypsum plus organic fertilizer is more significant.(2)The effect of different improvement measures on water conservation and water storage of 0-40cm soil layer is better,which can solve the problem of crop water shortage caused by uneven water distribution in time and space in the growth stage of sunflower,and the effect of biochar and desulfurized gypsum-plus organic fertilizer is more significant.With the extension of the application years of the improvement measures,the overall salt content of the soil surface is decreasing year by year,and the improvement measures can effectively reduce the content of K++Na+and HCO3-in the soil,reduce the soil alkalinity,compared with desulfurization gypsum and organic fertilizer,the effect is the best.In the third year of improvement,soil salt decreased 42.36%compared with the control.After three years of soil improvement,the middle and heavy salinized soil finally changed into light and medium salinized soil.(3)It can be seen from the analysis of the daily variation of soil carbon flux that the total carbon flux emission in the day is larger than that in the night,the daily average emission flux of CO2 in DJM,DJ and DC is smaller,and the daily average emission flux of CH4 in DJM,DSF,DC and DS is smaller.Regression analysis showed that the daily emission fluxes of CH4 and CO2 were positively correlated with soil temperature of 10 cm.(4)Based on the analysis of the seasonal and interannual variation characteristics of greenhouse gas emissions,it can be seen that after three years of application of the improvement measures,the seasonal average CO2 emissions of DJM,DJ,DSF,DC and DS decreased by 0.58%,2.73%,21.21%,24.51%and 9.10%respectively compared with the control.Compared with the control,the average CH4 emission fluxes of DJM,DJ,DC and DS decreased by 48.50%,39.09%,29.25%and 19.34%.Compared with the control,the average N2O flux of DJM,DJ,DSF,DC and DS decreased by 41.96%,0.27%,26.17%,42.86%and 1.07%respectively.At the same time,the improvement measures can reduce the comprehensive warming potential of CH4 and N2O in farmland soil,and ultimately reduce the intensity of greenhouse gas emissions,among which biochar,desulfurization gypsum,organic fertilizer and straw deep burying are better.(5)All the improvement measures can promote the growth of plant height and stem diameter,increase the leaf area and dry matter accumulation of sunflower,and biochar treatment is the most significant.Five improvement measures can improve the yield and 100 grain quality of sunflower.The yield of biochar and desulfurized gypsum with organic fertilizer increased by 45.24%and 35.71%respectively.To sum up,different improvement measures can effectively improve the physical and chemical properties of soil,improve the growth indicators of sunflower,increase production,and reduce greenhouse gas emissions from farmland.Therefore,it is of great significance to apply various improvement measures in the salinized soil of Hetao irrigation area for the management of saline alkali land,the development of agricultural economy and the protection of ecological environment.Among them,in terms of comprehensive three-year improvement effect,the application of biochar 22.5t/hm2 can better achieve the goals of saline alkali soil improvement,sunflower yield increase and carbon fixation and emission reduction,and has a certain long-term effect,followed by desulfurization gypsum and organic fertilizer. |
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