Study On The Regulation Of Soil Acidification As Affected By Water Nitrogen And Carbon In Farmland

Due to excessive nitrogen application,improper irrigation,acid rain and other reasons,acidification and deterioration of soil quality have became more and more serious as well as nutrient loss in the last 30 years in China.Soil acidification in some soils,especially in protected fields for vegetable production,is particularly serious and has became one of the main limiting factor of soil sustainable utilization.Based on the long-term fertilization experiments in China,the effect of different fertilization measures on soil pH change was investigated.A field experiment was conducted to study the optimization dosage of water and nitrogen input to improve crop nitrogen absorption and utilization,and reducing soil acidification resulted from nitrate leaching.Excessive nitrogen application in protected greenhouse soil with long growing history was also investigated,to explore the soil nitrogen transformation process and its effects on soil acidification.Though the effects of biochar on greenhouse soil and the inhibition of nitrification,the optimization dosage and corresponding technical measures of biochar use to retard soil acidification was investigated.The main results are as follows:1.Research results from long-term fertilization field trials indicated that long-term single application of nitrogen fertilizer and its combined application with phosphate,potassium fertilizer?N,NP,NK,NPK?accelerated soil acidification process and resulted in the decrease of soil pH value in all sites except in Hangzhou paddy soil.The pH of Hangzhou paddy soil was slightly increased when N,NP,NK and NPK were applied for a long period of time.Long-term application of organic fertilizer or combination of organic and inorganic fertilizers effectively alleviated the acidification process of red soils in Qiyang and Jinxian,and decrease the acidification in the red soils.In this study,when nitrogen,phosphorous and potassium fertilizer combined with organic fertilizer?NPK+M?in Zhengzhou fluvo-aquic soil,Chongqing purple soil and Gongzhuling black soil,the soil pH kept relatively stable,and slightly reduced in Zhengzhou fluvo-aquic soil.The effect of organic materials on soil pH change probably influenced by the nature of the organic materials,and the relatively application ratio of nutrients from organic and inorganic sources.Long-term application of inorganic nitrogen fertilizer has a significant impact on the annual pH change rate of soil.The annual pH change rate of different types of soil response to nitrogen application is red soil>tidal soil,purple soil>black soil>paddy soil.Long-term application of organic fertilizer increased soil pH value and retard soil acidification process,which is one of the important measures to prevent and control soil acidification.2.The combination of water and nitrogen levels to reduce nitrate leaching effect on soil acidification was studies in this research.The results showed that controlling soil water content under60%-70%of field capacity,applied amount of N fertilizer under 195-240 kg/hm² could effectively reduce soil NO₃^--N leaching and accumulation of nitrate in the lower soil profile section,which directly or indirect reduce the soil acidification potential resulted from nitrate leaching.With this optimized use of water and fertilizer,the highest yield of winter wheat with 8104.6-8500 kg/hm² was achieved.Rational regulation of water and nitrogen management with reduced nitrate leaching,improved water and nitrogen utilization efficiency is an effective measure to prevent and mitigate soil acidification.3.The results of field experiments on different nitrogen fertilization rates in two protected greenhouse soils in Beijing showed that different nitrogen fertilization treatments reduced soil pH by0.11-0.67 and 0.07-0.63 units,respectively,while soil conductivity?EC?increased significantly.The content of exchangeable acid and exchangeable aluminum increased with the increase of nitrogen application rate.Under the treatments of 225,450,675,900 kg N/hm²,H⁺released to the two soils were 22.41,43.2,98.28,156.33 and 1.89,10.64,22.06 and 32.4 kmol,respectively.It indicated that nitrogen application lead to an increase in H⁺content in protected greenhouse soils,which was one of the main reasons leading to the acidification of field soil.Excessive nitrogen application has a significant effect on CEC.Compared with the control?CK?,the nitrogen treatments in the two tested sites decreased soil cation exchange capacity?CEC?by1.83-6.27%and 1.94-6.8%,respectively.The decrease of CEC may be related to the decrease of soil pH caused by nitrogen application and the change of surface electrochemical properties of colloids with variable charge.However,soil salt base saturation?BS?was also reduced,and Ca²⁺and Mg²⁺were mainly reduced by different nitrogen fertilization treatments.Different nitrogen fertilization treatments had a significant impact on the distribution of pH,NH₄⁺-N,NO₃^--N in different soil profiles in the greenhouse soils.The effect of different nitrogen fertilization treatments on soil pH of different soil layers was related to NO₃^--N leaching.This indicated that the pH value of the soil in the greenhouse was significantly affected by NO₃^-.Excessive nitrogen application lead to the leaching and accumulation of NO₃^-and accelerates the soil acidification process.4.The biochar addition significantly increased the greenhouse soil pH value,CEC and organic matter by 0.13-0.44 pH units,5.39-25.99%and 6.14-18.6%,respectively.The improvement of greenhouse soil organic matter and CEC content is beneficial to the improvement of soil pH buffering capacity in acid soils.To solve the problem of soil acidification caused by soil nitrification from excessive nitrogen application,the adsorption performance of biochar can absorb soil NH₄⁺and reduce the content of NH₄⁺in the substrate during nitrification.On the other hand,biochar can reduce the number of soil ammonia-oxidized microorganisms,retard or inhibit the nitrogenous nitrification process in the soil,and thus reduce the amount of H⁺produced by the nitrification reaction.Biochar addition plays an important role in retard the soil acidification process in the protected greenhouse or improving soil pH.In Summary,The effects of long-term fertilization on the soil pH value were related to soil type,fertilizer management and planting methods.Long-term single application of nitrogen fertilizer accelerated soil acidification process,long-term application of organic fertilizer retard soil acidification process,which is one of the important measures to prevent and control soil acidification.Rational regulation of water and nitrogen management with reduced nitrate leaching,improved water and nitrogen utilization efficiency is an effective measure to prevent and mitigate soil acidification.Excessive nitrogen fertilization reduced soil pH and soil cation exchange capacity?CEC?in protected greenhouse soils,lead to pH buffering capacity of the greenhouse soil is reduced.The biochar addition significantly increased the greenhouse soil pH value.