Changes Of Nutrient Balances In Soil In Midwest Region Of Guanzhong Plain

Guangzhong plain is the main region of industry and grain in Shaanxi Province, and it isalso one of the irrigation regions and high degree intensive agriculture areas in China. SinceChina adopted the reform and opening-up policy, the agricultural production in this region hasdeveloped rapidly. The proportion of cash crop and farmland fertilization level has beengradually increasing as well. The phenomenon that unbalanced fertilization in some regionsbecomes serious, leading to the obvious changes of soil nutrient balance. All of the abovetrigger ecological environment problems.Based on the previous problems, this study took nutrirnt balance theory as the guide,using field experiment and nutrient balance investigation to analyze the balance condition ofsoil nutrient in farmland plot, farmers and regional scales. Aim to provide a theoretical basisof stable and high yield, sustainable development of resource and environment friendly. Themain results were as follows:1. Regarding the8-year maize-wheat rotation experiment in Yangling as the researchsubject, investigate the nutrient balance of N, P₂O₅and K₂O in different cultivation patternand N use. The results showed, as the times went on, the outcome of N, P₂O₅and K2Odecreased while the balance increased in different cultivation pattern and N use. In the8years,the N balance rate of mulching and furrow were respectively9.9%and0.6%, while the Nbalance rate of convention and water-controling were minus. So, mulching and furrow werehelpful for N balance; mulching, furrow and water-controling were more helpful for P₂O₅balance than convention; mulching and furrow were helpful for K₂O balance and mulchingwas better than furrow. By comparison of different N application rate treatments, the averageN balance rates of N0, N₁₂₀and N₂₄₀were respectively85.4%,-1.2%and74.9%. The averageN balance rate of N₂₄₀ was far higher than20%, so it will cause serious environmentproblem when apply240kg/ha N fertilizer into soil. There was no difference in P₂O₅and K2Oaverage balance rates between N₁₂₀and N₂₄₀treatments, which ranged respectively from－44.5%to－44.9%and from-228.3%to-241.9%. Long term deficit of P₂O₅and K₂O couldcause the degradation of soil fertility, so it should increase the application amount of P₂O₅properly considering the after-effect and increase the application amount of K2O.2. Regarding Fufeng County household survey date as the research subject, we investigated the fertilizer use and soil nutrition in the wheat-maize rotation system during16years by using the investigation and nutrient balance method. The result showed that since1994, the mean annual growth rate of the inputs of nitrogen and phosphorus fertilizer in wheatand maize was higher than that of the yields of wheat and maize, indicating that the utilizationefficiency of nitrogen and phosphorus fertilizer has been decreasing gradually. The per unitarea of wheat and maize field, the amount and concentration of nutrient provided by fertilizerhad increased, while the amount and concentration of nutrient provided by organic fertilizerhad decreased. The pre unit balance index of N, P₂O₅and K₂O in wheat and maize field had arelationship with the pre unit organic fertilizer use. The pre unit balance index of N, P₂O₅andK₂O decreased as the use of organic fertilizer decreased. In the16years, the balance index ofN, P₂O₅and K₂O has decreased, but N and P₂O₅have been in surplus while K₂O has been indeficit. In the16years, the accumulations of N, P₂O₅and K₂O were respectively2268.3,4273.3and274.1kg/ha. The over-surplus of N and P₂O₅could raise the risk of non-pointpollution and the balance of K₂O could be in deficit. Fufeng County should increase the useof organic fertilizer and K₂O fertilizer and decrease P₂O₅fertilizer properly to balance the soilnutrient, improve the soil fertility, and accomplish the sustainable development of agriculture.3. Regarding Fufeng County as the research subject, we investigated the balance offertilizer use and soil nutrition in16years by using the investigation and nutrient balancemethod. The results showed, since1994, pre unit use amount of fertilizer has increased. Itspercentage of total nutrient increased from60.8%in1994to88.3%in2009, while thepercentage of organic fertilizer decreased from26.9%in1994to4.4%in2009. The amountof pre unit N and P₂O₅has been in surplus and the surplus amount of P₂O₅was higher than N.The amount of pre unit K₂O has been in deficit and the change of deficit rate was stable andaveraged at-54.1%. As the structural adjustment for crop production was continued,especially the increase of cash crop area, Fufeng County should take the "decrease N, controlP and increase K" action to avoid the over-surplus of N and P₂O₅and the deficit of K₂O whichcould lead to the non-point pollution and decline of soil fertility.4. In this study, we analyzed the nutrient inputs and outputs in soils of the northern areasof Qinling Moutain in Shaanxi, including Zhouzhi, County Hu and Chang'an in1980－2009,with data and parameters obtained from agriculture statistical reports and references in theregion. The results indicated that since1980, both the nutrient input from chemical fertilizerand organic fertilizer had an increasing trend, especially the nutrients from chemical fertilizer.The proportion of chemical fertilizer to total nutrient input in the region increased from47.5%in1980to75.4%in2009, whereas the proportion of organic fertilizer to total nutrient inputdeclined from34.6%in1980to18.8%in2009. Nitrogen balance in soil of the region was at surplus; phosphorus balance became positive since1990, instead of deficiency in1980; andpotassium balance was still in negative, but the negative rate became less and less. To preventthe non-point pollution caused by the excessive accumulation of nitrogen and phosphorus insoil in the north region of Qinling moutain of Weihe River in Shaanxi, we suggest controlingthe application rates of nitrogen and phosphorus fertilizers and increasing potassium fertilizerin the agriculture.