Research On Characteristics And Mechanism Of Brown Earth Acidification In Liaoning Province

Soil acidification is one symptom of soil degradation either. The topics of acidification mechanism, objectivity of space-time evolution and reconversion have been the hot issues that concerned by soil scientist, agronomist and environmental chemist. The survival and development space of human seriously threatened by the disaster of soil acidification. Brown earth is the main type of cultivated soil. Recent research showed that pH of brown earth significantly decreased due to the unreasonable tillage and fertilization, and the mechanism of it needs further study. Based on this situation, the statues of brown earth in different areas had investigated in this study by comparing with the second soil census. The characteristics of soil pH and the rules of base cations changed in different fertilizer treatments had studied by means of the long-term experimental field. The constituent and relative amount of clay minerals in different fertilizer treatment was tested. The characteristics of nitrogen migration within different soil moisture content and nitrogen rate, effects of migration and leaching of nitrogen on base cations has been study, either. The main results were as follows.1. Significant differences of soil pH were in different districts of Liaoning province. The area of acid arable brown earth in the east, north and middle Liaoning province took the large part while the south and west were relatively small. The acid area of arable brown earth in Qingyuan and Kuandian districts, which in the east of Liaoning province took the large parts, the values were21.91%and51.91%, respectively. The area in west and south Liaoning province were small which both below5%. The brown earth pH significantly decreased comparing with the second soil census. Area of weak acid and acid both increased while the neutral area decreased.2. The significant differences of subsoil were in different districts. Subsoil pH in soil profile of Kuandian district, which is in the east of Liaoning province was lower than the other district and the pH was in the acid range. However, pH of this district increased after tillage. The subsoil pH of Qingyuan, Kaiyuan and Shenyang districts was weak acid while the topsoil pH of them was relatively delined. A decreasing trend was found in cation exchange capacity as pH decreased. Base saturation were more than70%while pH range were from6.6to7.0, however, base saturation were lower than60%while pH range were from4.6to5.5. 3. Significant affects of soil pH were found after long-term fertilization. The decreasing of1.31pH unit-1applying urea with the nitrogen rate of270kg N hm-2after27years tillage. The pH buffer capacity decreased3.87mmol kg-1pH unit-1. The reduce extent of pH was increased when adding phosphate and potassium fertilizer based on nitrogen fertilizer. The degree of soil acidification will be relieved when applying organic and inorganic fertilizer. A non-significant difference was found in restraining soil acidification of applying nitrogen fertilizer (120kg N hm-2) only while the organic rate was75.6kg N hm-2. However, the difference was significant when the organic fertilizer rate was increased to135kg N hm-2. The contents of exchangeable acid and exchangeable Al3+increased as the nitrogen rate increased.1320、1500、1980and3780kmol hm-2exchangeable acid will be add to soil with the nitrogen rate of120、135、180and270kg N hm"2. Soil pH buffer capacity was significantly decreased and the weathering of illite was accelerated, the content of illite was significantly decreased while the content of kaolinite,1:1type mineral, was increased after long-term applying urea which will easily lead to soil acidification.4. The maximum of NH4+-N was found in the first21days after applying urea to soil. However, the content of NO3--N increased after the incubation time of21days. The speed of nitrification rate controlled the process of soil acidification in no leaching condition. Declining of base saturation after migration and leaching was the mechanism of substantiality of soil acidification. NH4+-N easily transformed to NO3--N and nitrification was intensively when the soil moisture was70%. NO2--N production with soil moisture of50%was lower than that of70%. Nitrification rate delayed and the date of nitrification was hysteretic when soil moisture was100%.5. Base cations of soil colloid were replaced by NH4-at the beginning of nitrogen transformation, which will increase potential menace of base cations losses. Leaching amount of base cations were due to the accumulation of NH4+in the earlier stage, while the accumulation of NO3-was the main factor in the later period. A significant positive correlation was found between soil pH and NH4+-N in nitrogen transformation stages of the first30days, while a negative correlation was found between pH and NO3-N from30to90days incubation. Leaching amount of base cations increased gradually and pH of leachate showed the maximum value during the first45days. Acidification trend was found in topsoil of soil columns after120days leaching, reduction rate of pH increased as nitrogen rate increased. Significant acidification phenomenon was found in the nitrogen rate of450mg kg-1with pH decreased0.51unit-1comparing with control.