| In farmland ecosystem, the balance of soil nutrients is the base of stabilizing andincreasing yield of crop. Research of nutrients balance in farmland can help looking into thevariety and problem possibly appeared in process of farmland nutrients degenerate andregenerate from macro angle. Furthermore, there has geography space-time otherness in thebalance and circulation of farmland nutrients geography space-time otherness, and the loessplateau has its own particularity. Therefore, doing research of the nutrient balance in the loessplateau has its practical signification. Using the long-term rotation and fertilization experiment that disposed in dry land on theloess plateau, the paper has studied nutrients in rainfall import to farmland ecosystem andAmmonia volatilization losses and nutrients disbursal of crop, also estimated the balance ofnutrients in farmland soil. N input with rainfall is an important method of N input in dry land on the loess plateau,its amount in a year is 6.72-10.80 kg/hm2, and it mostly happened between June andSeptember. Furthermore, there has distinctness correlativity between the amount of N,P,Kin rainfall and annual precipitation in this area. Ammonia volatilization losses of N are one of the important losses methods in dry land.Long-term application of organic manure can evidently decrease the Ammonia volatilizationlosses. Ammonia volatilization losses increased adapt to the hoist of temperature inexamination range. In period of nourishment growth, Ammonia volatilization losses velocityis very small and there is no evidently difference between winter wheat and alfalfa. But inprocreation growth period, it increased geminately. The amount of ammonia volatilizationlosses in a year is about 3.99-9.37kgN/hm2. Proportion fertilization in reason can increase utilization ratio of fertilizer, decrease theratio of stalk/seed, and promote nutrients moving to economic yield. The same crop hasdifferent nutrients wastage under different fertilization, N wastage has minimum of3.77kgN/100kg economic yield under fertilization of 72.44kgN/hm2 and 46.90kgP/hm2. Pwastage has minimum of 0.61 kgP/100kg under fertilization of 124.97kgN/hm2and29.61kgP/hm2. With the increasing of fixed number of year, nutrients content in wheat stalkand seed decreased, that in alfalfa increased. Fertilization has less effect on the content of soil organic C, organic fertilizer appliedwith mineral fertilizer can increased soil organic C content evidently. Crop cultivation canincrease soil N supply ability, increase range is between 6.88% and 36.58%, the most of itis alfalfa, and its increase amount is 1.37 times of bareness. Content of soil organic C ,totaliii AbstractN and available N increased evidently, but total P and available P decreased in some degree,when leguminous plants induct into rotate system. Furthermore the content of total N andavailable N in plough layer increasing with the fixed number of year. Long-term fertilizationcan increase soil nutrients content evidently is because of crop can't uptake all the nutrients infertilization and the nutrients cumulated in soil. It can supply crop nutrients requirement andcan't cause nutrients cumulated in soil with the fertilization of N 51.89 kg/hm2 , P11.90kg/hm2. Estimate nutrients status in this area, the result showed that, there is surplus 21.47-32.48% of fertilizer N and 44.54-74.56% of fertilizer P. K has 2.45-6.29 kg/hm2·a to the badlack of fertilizer K. Therefore, it should stabilize N , K fertilization and decrease Pfertilization.
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