Experimental Studies On The Coupling Response Of Water-carbon-nitrogen Migration To Different Irrigation Methods And Biochar In The Salinized Farmland

Hetao Irrigation district in Inner Mongolia is an important commodity grain base of the country.However,the shortage of water and higher degree of soil salinization are major factors restricting the development of agricultural production in the region.Optimizing irrigation methods and agronomical practtces have great significance to solve these problems,when facing water shortages,worsening environmental pollution,the challenge of food security in this district.Crop stalk biochar has the characteristics of carbon fixation,high specific surface area,porous and strong adsorption.It plays a positive role in improving the structure of soil,increasing crop yield and reducing greenhouse gas emission.However,there are few study reports in the effect of biochar application and research in salt and alkali land improvement of our country.There are different effects on soil water and heat environment of different irrigation,due to different frequency and irrigation amount of border irrigation and drip irrigation.Whether the application of biochar into the soil with different irrigation methods becomes a new way for improving agriculture potential productivity,crop high efficient use of water,as well as the control measures for the comprehensive effect of carbon sequestration and carbon emission reduction of greenhouse gases in farmland,which is worth further exploring in Hetao Irrigation district.Therefore,Two-year field experiments were conducted in a coastal reclamation zone of Linhe winery ecological park in Bayannaoer city of Inner Mongolia.In this study,three different irrigation methods were used traditional border irrigation in different water quality?Yellow River water,groundwater?and drip irrigation of underground water,and whether biochar was added as a contrast under same or different irrigation methods.Experimental research on the effects in crop growing,soil nutrient changing and greenhouse gases emission under different irrigation methods,and compares and analyzes the soil physical and chemical properties,soil temperature,crop growth,soil nutrients and greenhouse gases emission when added biochar into soil under different or same irrigation methods.At the same time,selecting the best biochar and nitrogen ration under drip irrigation.It will provide a scientific way for optimizing moisture content and nutrient management on farmland and improving carbon sequestration and emission reduction capacity and resource utilization in Hetao Irrigation district.The main results of this study are as follows:?1?The coupling of different irrigation methods and biochar significantly affects the basic properties of soil.It has a positive effect on improving soil water content,but also aggravates soil salt accumulation,and has no significant effect on soil pH.i)The water content of 0-40cm soil layer was significantly increased by drip irrigation+biochar than border irrigation+biochar,which was 6.47%⁹.75%higher than that of the border irrigation ofYellow River water+biochar and 7.62%¹1.08%higher than that of border irrigation of ground water+biochar.ii)The salinity of border irrigation of groundwater and border irrigation of Yellow River was increased8.91%²6.58%,4.43%¹7.83%,respectively.The salinity of drip irrigation+biochar decreased 12.18%¹8.52%inner membrane and 5.87%¹6.88%increased outside the membrane.?2?The coupling of different irrigation methods and biochar has different effects on soil temperature.i)The coupling of drip irrigation with biochar improved soil temperature 1.20%³.87%,however,the coupling of border irrigation of Yellow River wate and groundwater with biochar decreased 0.80%².40%,1.01%⁵.15%,respectively.ii)Biochar is a medium for reducing the heat exchange of soil and atmosphere.It has a certain hindrance to the two-way heat movement and can effectively stabilize the fluctuation of soil temperature.?3?The coupling of drip irrigation methods and biochar can significantly promoted growth of maize,increased maize grain yield,water use efficiency and nitrogen partial productivity.The grain yield of drip irrigation with biochar was improved 9.16%¹4.70%and 11.03%¹2.29%,and the water use efficiency increased by 45.90%¹08.11%,58.30%¹10.38%,and the partial productivity of nitrogen fertilizer increased 82.29%¹22.07%and 124.58%¹29.41%,respectively than that of the border irrigation of Yellow River water and border irrigation of groundwater with biochar?4?In northern dry farmland,the soil generally absorbs CH₄ from the atmosphere.Border irrigation increased the emission of CO₂ after application biochar,but drip irrigation reduced the greenhouse gases from soil.The emission of greenhouse gases is significantly related to soil temperature and moisture content.i)The coupling of border irrigation of groundwater with biochar made the emission of soil CO₂ and N₂O increased 42.50%⁴6.50%and 10.91%¹7.59%,respectively,and the border irrigation of Yellow River water with biochar made CO₂ emissions increased 0.42%³.65%,N₂O emission reduced 57.60%¹49.21%,and CO₂ and N₂O emissions of underground water drip irrigation with biochar decreased 50.14%⁵9.18%?102.82%¹96.42%respectively.ii)Under the drip irrigation,with the increase of the amount of nitrogen application,the emission of soil CO₂ showed a tendency to decrease first and then increase with the amount of nitrogen application.The emission of soil N₂O was still increasing with the increase of the amount of fertilizer.But under the same amount of nitrogen application,the nitrogen level of N2with biochar could significantly inhibit the emission of N₂O and CO₂ in soil.The amount of CO₂ and N₂O emissions decreased 10.00%¹5.60%,30.07%⁵6.20%,and CH₄ uptake increased 91.45%⁹5.27%.In this experiment,the best combination amount of biochar application and nitrogen fertilizer was 30t/hm² and 375kg/hm²?5?The Coupling of drip irrigation and biochar could significantly reduce nutrient loss of soil.i)The nitrate nitrogen and ammonium nitrogen in drip irrigation were mainly accumulated in 0-40cm.of soil layer,while border irrigation was mainly accumulated in 20-70cm of soil layer.The application of biochar in the same irrigation methods significantly increased the accumulation of 0-100cm nitrate nitrogen and reduced the accumulation of ammonium nitrogen.The nitrate nitrogen in the border irrigation of Yellow River water and groundwater,and drip irrigation increased 6%¹5.70%,1.60%⁷.20%,3.23%⁷.67%,and the accumulation of ammonium nitrogen decreased 1.22%⁷.32%,2.93%⁹.66%,2.83%⁸.08%.iii)Under drip irrigation,the accumulation of nitrate nitrogen and ammonium nitrogen in soil increased with the amount of fertilizer application,showing N3>N2>N1;After adding biochar,the amount of nitrogen application is 375kg/hm²,which greatly improved the soil nitrate nitrogen accumulation and reduced the content of ammonium nitrogen in soil.