Impact Of Long-term Chemical Fertilizer Application On Nitrogen, Phosphorus And Enzyme Activities Of Black Soil

This study was conducted to examine the nutrient status of the black soil based on long-term fertilization experiment in National Field Research Station of Agro-ecosystem in Hailun, northeast China.We selected the soil nitrogen,phosphorus and soil enzyme activity the as the indicators of long-term study of black soil fertility and fertilizer application of quality change in order to reveal the impacts of long-term application of fertilizer on black soil fertility and the practice of optimizing agricultural production,rational,scientific way of fertilizer and fertilizer ratio,and obtain high-quality and high-yield crops under the premise of improvingthe soil fertility and further providing a scientific basis for sustainable development of agro-ecosystem on the basis of long-term experiment to elucidate NPK cycle and balance characteristics.The experiment began in 1990,including seven treatments:(1) CK(no fertilizer district),(2) NP,(3) NK,(4) PK,(5) NPK,(6) NP₂K,(7) NPK₂.Soil nitrogen,phosphorus,the activity of soil enzyme and crop yields were determined.The results showed that:The crop yields changed significantly corresponding to different fertilzer application.Wheat,maize and soybean yield of no fertilizer application treatments(CK) decline 38.8%,37.8%and 9.4%with NPK treatment respectively,However,the crop yields, strongly affected by climate,did not significantly change annually.In black soil,impact extent of NPK about the crop yields is N＞P＞K,the crop yields of NPK application in balance are maximal.No fertilizer application led to decrease of total soil nitrogen,while nitrogen fertilizer application increased total soil nitrogen.Long-term fertilization had a pronounced effect on the mineralization and nitrification processes,showing that chemical fertilizer application increased the content of mineralized nitrogen.The nitrification rates had a strong relationship with nitrogen fertilization.Potassium influenced the efficiency of fertilizer utilization much more than phosphorus,and balance fertilization increased the efficiency of fertilizer utilization.Excessive application of P and K fertilizer did not enhance the efficiency of nitrogen fertilizer utilization.60mg P kg-1soil was absorbed by crops during 12 years of no fertilizer application on the condition of the rotation of wheat-soybean-maize,and absorbed P of NK fertilizer application increased 35%as compared to no fertilizer application,in which organic P accounted for 26.7-29.7%,and absorbed inorganic P included Ca₂-P,Ca₈-P,A1-P and Fe-P which showed similar absorbed amount and can be available sources for black soil.Regardless of P absorbed by crops,most of applied P fertilizer deposited in soil of 0-20cm layer which increased the content of available P depending of fertilizer varieties and application amout.The residue P existed in the form of Al-P,Fe-P and Ca8-P in black soil.The loss and gain amount of soil P was significantly correlated with total soil P and soil available P,the fitted equations were:Y=0.02+1.01X and Y=2.08+0.15X.Long-term fertilization increased the activity of soil phosphatase,urease and converting enzyme at the depth of 0-20cm and 20-40cm,the increment are 16.2%-104.4%,12.1%-48.5%,19.2%-51.9%(0-20cm) and 69.8%-165.5%,3.3%-41.8%,21.6%-86.7%(20-40cm) respectively, but had little effect on soil catalase activity.Long-term nitrogen and phosphorus application enhanced the activity of soil urease and phosphatase,respectively.