Impact Of Electric Field From Soil Particle Surface On Ammonium Transportation And Nitrification

Fertilization is critical in crop yield raising and quality improving. With the rapid development of agriculture, inevitably the demand for nitrogen fertilizer will increase rapidly . However, nitrogen use efficiency is generally low currently, and a huge amount of fertilizer loses. The reasons of low utilization efficiency of nitrogen fertilizer are: First, the partial ammonium ion will enter the water body along with the colloid pellet outflow; second, while there is still a considerable part of nitrogen fertilizer turn to nitrate nitrogen in the nitration, and Enters the water along with the carrier by the surface runoff and groundwater runoff's, and cause the pollution of groundwater, rivers and other water bodies. Because the NH₄⁺ takes positive charge, formidable negative electric field of soil will reduce the activity of ammonium ion, so that it may prevent it migrate, motive, and turn into nitrate with the colloid, but how much the effect on "the impediment" of soil electric field has not carried on quantitatively and systematically. Now with the establishment of Determination of solid particles surface and electric field strength, we can do a systematic quantitative research.This article used constant current method to mensurate and calculate the surface charge quantity, surface potential, surface charge density, surface electric field intensity and specific surface area on neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite. We also used the constant current method to research the process of ammonium ion diffusion and transmission in different surface electric field (neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite) and constitution of electric double layer ion (K, Mg), and analyzing the impact of soil surface electric field and electric double layer ion on transmission and diffusion and rate of ammonium ion. Finally, researching the nitrification on different surface electric field (neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite) and constitution of electric double layer ion( K, Mg), and analyzing the impact of soil surface electric field and electric double layer ion on ammonium ion's process and rate of nitrification. The experimental result as follows.Firstly,in 1.09×10^-4mol.m^-3NH₄Cl electrolyte, using constant current method, the conclusion is: the surface potential of neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite is -0.31V, -0.33V,-0.36V respectively; the surface density is 0.26 C m^-2,0.39 C m^-2,0.69 C m^-2 respectively; The surface electric field intensity is -1.2×108 V/m,-1.77×108 V/m,-3.17×108 V/m respectively. After joining the montmorillonite, the surface potential, surface density, Surface electric field intensity of neutral purple soil are increased, and more increasing the quality of the montmorillonite, the increase are more.Secondly, Along the transmission which the direction is potential reduce (adsorption process), ammonium ion diffusion kinetics in neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite find that, the negative first-order kinetic process did not appear,and the zero-order kinetic process did not exist.In first-order kinetic: the absorption quantities of NH₄⁺ is the highest and the rate of diffusion is the fastest in neutral purple soil+10%montmorillonite; the absorption quantities of NH₄⁺ is the lowest and the rate of diffusion is the slowest in neutral purple soil. The transient absorption quantities of NH₄⁺ in K saturation is more than in Mg saturation,and the rate of diffusion is faster than in Mg saturation.From this we can see that surface electric and constitution of electric double layer ion impact on the NH₄⁺ diffusion and transmission,and the electric field strength is stronger, the rate of diffusion is more fast along the transmission which the direction is potential reduce (adsorption process).Thirdly, along the transmission which the direction is potential increase (desorption process), ammonium ion diffusion kinetics in neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%montmorillonite find that, in this three different surface potential of the soil samples, the desorption quantities of NH₄⁺ is the lowest and the rate of diffusion is the slowest in in neutral purple soil+10%montmorillonite; the desorption quantities of NH₄⁺ is the highest and the rate of diffusion is the fastest in neutral purple soil.The transient desorption quantities of NH₄⁺ in Mgcl₂ is more than in KCl,and the rate of diffusion is faster than in KCl. From this we can see that surface electric and constitution of electric double layer ion impact on the NH₄⁺ diffusion and transmission,and the electric field strength is stronger, the rate of diffusion is more slow along the transmission which the direction is potential increase (desorption process).Fourthly, the nitrification of NH₄⁺ in neutral purple soil, neutral purple soil+5%montmorillonite and neutral purple soil+10%monrmorillonite is as follows. In the initial phase, the quality of nitrate nitrogen is most in neutral purple soil, and the average nitrification rate of ammonium ion is the fastest. the quality of nitrate nitrogen is least in neutral purple soil+10%montmorillonite, and the average nitrification rate of ammonium ion is the slowest. The quality of nitrate nitrogen in KCl electrolyte is lower than in MgCl₂ electrolyte's. The average nitrification rate of ammonium ion is in KCl electrolyte is lower than in MgCl₂ electrolyte's. However, the study showed that in different types of Surface electric field and electrolyte, the total quantity of nitrate nitrogen tends to be consistent about 10 days later. The soil surface electric field and constitution of electric double layer ion affect the average rata of nitrification.