Modified Biochar And γ-Polyglutamic Acid On Nitrogen Transport And Transformation In Black Soil

Black soil,as the main cultivated soil in China,is one of the important land resources due to its fertile soil and abundant organic matter.However,currently in black soil areas,the"one shot"fertilization method is often used,which has a low nitrogen utilization rate.A large amount of unused nitrogen enters the water through runoff and leaching,exacerbating the risk of agricultural non-point source pollution.The inorganic nitrogen in the soil has strong mobility,especially the soil has very weak NO₃^--N fixation capacity,and NH₄⁺-N will further generate NO₃^--N through nitrification,accelerating the loss of nitrogen in the soil.Therefore,this article studied the addition of metal ion modified biochar andγ-Polyglutamic acid to soil,to explore its impact on the migration and transformation of inorganic nitrogen in black soil.Enhancing the soil’s ability to retain inorganic nitrogen through modified biochar,γ-Polyglutamic acid weakens the rate of ammonia oxidation in soil and to achieve the goal of reducing the loss of inorganic nitrogen in the soil,provide technical support for the prevention and control of agricultural non-point source pollution.The research results are as follows:（1）Preparation and screening of modified biocharThe modification of straw biochar with potassium,zinc,and iron ions can increase the specific surface area and average pore size of biochar by 2.99-9.35 times and 2.38-6.67 times,respectively.Potassium,zinc,and iron modifications can significantly enhance the adsorption capacity of biochar for NO₃^--N and NH₄⁺-N,Among them,Fe-BC has the highest adsorption capacity for NO₃^--N and NH₄⁺-N,with 24632.8 and 5253.7 mg/kg,respectively.Therefore,Fe-BC is determined as the best modified biochar.（2）Fe BC andγ-Polyglutamic acid on Nitrogen Adsorption by Black SoilUsing black soil as a control（CK）,add 3 mg/g of Fe-BC（TB）to the black soil.Add Fe-BC to black soil while adding 5μG/gγ-Polyglutamic acid（TBP）.The adsorption processes of CK,TB,and TBP for NO₃^--N and NH₄⁺-N show a trend of first fast,then slow,and finally reaching equilibrium.The adsorption equilibrium time is all 480 minutes.The Elovich equation shows a significant correlation between the adsorption of NO₃^--N and NH₄⁺-N.The adsorption isotherm of CK,TB and TBP all conform to Langmuir equation.The adsorption process of NO₃^--N is spontaneous,exothermic and disordered,and the adsorption process of NH₄⁺-N is spontaneous,endothermic and disordered.The saturated adsorption capacities of CK,TB,and TBP for NO₃^--N and NH₄⁺-N can reach 440.8,2334.4,2346.6 mg/kg and 2384.1,3570.0,3652.1 mg/kg,respectively.Adding Fe-BC to black soil can effectively enhance its adsorption capacity for NO₃^--N and NH₄⁺-N;becauseγ-Polyglutamic acid on improving nitrogen adsorption capacity is not significant,so its adsorption effect on nitrogen is weak.The adsorption capacity of the tested soil for NH₄⁺-N is significantly higher than that of NO₃^--N.Within the pH range of 3-9,all three treatments had the highest adsorption capacity for NO₃^--N at pH=3;CK has the highest adsorption capacity for NH₄⁺-N at pH=9,while TB and TBP have the highest adsorption capacity for NH₄⁺-N at pH=5.（3）Fe BC andγ-Polyglutamic Acid on Nitrogen Leaching in Black SoilThe results of the leaching test indicate that,the cumulative leaching of NO₃^--N and NH₄⁺-N in TBP decreased by 27.71%and 39.35%compared to CK,and decreased by 3.72%and 5.08%compared to TB;the cumulative leaching of NO₃^--N and NH₄⁺-N in TB decreased by24.92%and 36.10%compared to CK.The cumulative leaching amount of NO₃^--N in TB and TBP is still significantly higher than that of NH₄⁺-N.（4）Fe BC andγ-Polyglutamic Acid on Nitrogen Transformation in Black SoilThe conversion test results showed that the soil ammonia oxidation rate of each treatment was in descending order:TB>CK>TBP;due to the lowest ammonia oxidation rate of TBP,the NO₃^--N content in TBP is the lowest,and the risk of inorganic nitrogen leaching is reduced.The changes in pH value of each treatment from large to small are TB>CK>TBP.Due to the strong adsorption effect of Fe-BC itself,it can enhance the soil’s ability to fix inorganic nitrogen by adding it to the soil,thereby reducing the loss of inorganic nitrogen in the soil.γ-Polyglutamic acid can also serve as a semi nitrification inhibitor,inhibiting ammonia oxidation rate,reducing NO₃^--N content in soil,and achieving the goal of reducing nitrogen loss in soil.