Study On The Influence Of Nitrogen Fertilization On Purple Soil Acidification And Surface Electrochemical Properties

Since the 1980s, the consumption of nitrogenous fertilizer in our country has increased dramatically. Long-term N fertilization especially the fertilization of ammonium nitrogen fertilizer caused a series of soil environmental problems of which soil acidification is the most serious. In South China, for the condition that there are many people and less land, purple soil is seen as important farming soil especially in Sichuan, Guizhou and Yunnan province. There are many studies on nutrient status and the influence of acid precipitation on soil acidification but studies on the influence of N fertilization on purple soil acidification are very few. On this condition, this paper studied the influence of nitrogen fertilization on purple soil acidification and surface electrochemical properties by simulated experiment in which we fertilized purple soil with different kind of nitrogenous fertilizer. The study aimed at providing a theoretical basis for the improvement of soil quality in South China, promoting the increasing of agricultural yield and income and the contributing to the improvement of peasants’living standard.①Without fertilization, the concentration of NO3- and K+, Na+, Ca2+, Mg2+in three stages was respectively in an order ofⅡ2>Ⅰ2>Ⅲ2, and that ofⅡ2 andⅢ2 is lager than that ofⅠ10 andⅡ10. No matter which sort of nitrogenous fertilizer, the content of released base cations all increased with the increasing of nitrogenous fertilization. In the urea treatment, the content of released K+, Na+, Ca2+、Mg2+under different nitrogen application of 100,200,300 and 400 mg·kg-1 was respectively 1.52-2.13,1.33-2.05,2.65-4.95 and 2.22-4.16 times of the control treatment; in the ammonium nitrate treatment, it was respectively 1.70-2.14、1.32-1.79、2.81-4.67、2.43-4.21 times of the control experiment and in the ammonium sulfate treatment, it was respectively 1.54-2.56、1.34-2.18、3.15-5.88、3.10-6.30 times of the control treatment. With same amount of nitrogenous fertilization, the influence of different sort of nitrogenous fertilizer on the release of base cations was different and the influence of ammonium sulfate was biggest and the influences of urea and ammonium nitrate on different base cations were different.②In the three stages of fertilization and leaching, the amount of nitrate radical was significant positive correlated with that of K+、Ca2+、Mg2+ and in N1 treatment, the correlation of NO3-and Na+ was very significant and in N2, N3, X1, X2 and X3 treatment, it was significant while in N4, X4 L1, L2, L3 and L4, there was no correlation.③After many times of fertilization and leaching, pH of purple soil all decreased and were in inverse proportion with the amount of nitrogenous fertilization. Compared with natural soil, being fertilized with urea, ammonium nitrate and ammonium sulfate in four different level of nitrogenous fertilization, of the soil decreased by 9.85%-19.85%,11.76%-23.09%and 23.53%-25.74% respectively. On the same level of nitrogenous fertilization, the pH of purple soil fertilized with ammonium sulfate decreased most, followed by ammonium nitrate and the least is urea.Compared with natural soil, the exchangeable hydrogen of the control soil changed very little but the amount of exchangeable aluminium increased four times.In the level of 100、200、300、400mg kg-1 N, compared with natural soil, the exchangeable hydrogen of soil in urea treatment increased by 0.31.82%, 45.45%and 63.64%and the exchangeable aluminium increased 11,16,20 and 28 times respectively;while in ammonium nitrate, exchangeable hydrogen increased by 10.00%,30.91%, 53.64%and 70.00%and exchangeable aluminium increased 13,26,39 and 55 times respectively;in ammonium sulfate treatment, exchangeable hydrogen increased by 332.73%,365.45%,444.54%and 502.72%and exchangeable aluminium increased 45,51,55 and 56 times. The influence of urea, ammonium nitrate and ammonium sulfate on exchangeable hydrogen and exchangeable aluminium was different, if the amount of fertilizer was the same, the order was ammonium sulfate> ammonium nitrate> urea and the influence of ammonium sulfate was much higher than that of urea and ammonium nitrate. After fertilization and leaching, the amount of exchangeable hydrogen and exchangeable aluminium all increased with the increasing of Exchange acid amount. Without being fertilized, the amount of released aluminium was limited and exchangeable hydrogen took up 72.20%of EA. Being fertilizered with urea and ammonium nitrate, the amount of exchangable acid was determined by exchangeable aluminium and being fertilizered with ammonium sulfate, the amount of exchangable acid was determined by both exchangeable hydrogen and exchangeable aluminium.④After many times of fertilization and leaching, the soil total exchangeable base(TEB) decreased compared with natural soil.The amount of Exchangeable Base Cations were in order of Ca2+>Mg2+>K+>Na+.The contents of exchangeable Ca2+and Mg2+in experiment soil were lower than that of natural soil and the amount of exchangeable K+decreased in treatments of N3, N4, X3, X4, L2, L3 and L4 compared with natural soil, while under other conditions it increased; the content of exchangeable Na+decreased in treatments of L2, L3 and L4 compared with natural soil, while under other conditions it kept unchangeable or increased.⑤After many times of fertilization and leaching, the soil base saturation(BS) all decreased. The descrease of CK was 0.14%, and that of urea treatment of four levels decreased by 0.65%,1.13%, 1.47%and 2.11%; that of ammonium nitrate decreased by 0.86%,1.74%,2.71%and 3.75%;while in ammonium sulfate treatment, the decrease was respectively 4.56%,5.49%,6.75%and 7.52%. No matter which sorts of nitrogenous fertilizer, the soil base saturation(BS) decreased with the increasing amount of nitrogenous fertilizer. ⑥Soil pH decreased with the increase of EA and increased with the increase of TEB and the foundation of EA was dominant.The correlation between pH and BS was very significant positive.⑦After fertilization and leaching, the specific surface area of purple soil all increased compared with natural soil. No matter being fertilized with which sort of nitrogen fertilizer, the soil specific surface area was all inversely proportional to the amount of nitrogen and on the same amount of nitrogen the specific surface area was in an order of urea> ammonium nitrate> ammonium sulfate.