| Internationally, people have recognized that fertilizer has both positive and negative roles:fertilizer is not only the basis of high quality and quantity of crops, but also the potential factor of environment pollution. Inappropriate fertilization may pollute the environment. Thus, to restore and increase the soil fertility, it is an important measure of scientific fertilization to return and compensate the decreasing and more and more insufficient nutrient of soil, which can make a continuous and steady increase of production of crops. Economic and reasonable fertilization of crops means that people can make the most profit by using the least fertilizer. The key of soil testing and fertilizer recommendation is building up soil nutrient plentiful and shortage indicators of different crops and different regions by the results of soil nutrient test and fertilizer field trials. The prerequisites of successful fertilizer field trials and balanced fertilization is to know more the soil nutrient information. System diagnosis of crop nutrient limiting factors in soil is considered to be the premise of establishment of the maximum yield. The combination system diagnosis of soil analysis, absorption experiment and instruction plants pot experiment can be a practical method which can monitor the dynamic changes of soil nutrient limiting factors fast and comprehensively.In this research, we collected135soils samples from Fangqiang Farm, Yancheng, Jiangsu in autumn,2009.11kinds of macro-, medium-and micro-element nutrient available content were detected in the lab. Absorption research of the main elements was carried out according to the results. Then start the pot experiment in the greenhouse to identify the limited factor in the soil. At last, carry out the corresponding field experiment to verify the results. The results were showed as follows:1. We basically mastered the distribution and the limiting factors of soil nutrients in that region, on the basis of the laboratory nutrient analysis. According to the soil test results of each monitoring sites, the average of the pH value, alkaline hydrolytic nitrogen, available P, available K and organic matter was8.407,80.897mg/kg,28.916mg/kg,179.892mg/kg and19.632mg/g. In general, the soil pH value was above7, and the content of alkaline hydrolytic nitrogen and organic matter was at the low level(60～90mg/kg and10～20mg/g), the content of available P was at the high level(20～40mg/kg), the content of available K was at the higher level(>160mg/kg), which showed that the content of available P and available K in this region was generally at the medium to rich level, organic matter and alkaline hydrolytic nitrogen were deficient in this region. According to the National Soil Survey Technical Standards, the soil available Zn and Mn in Fangqiang Farm were deficient, the ratio of the deficient and the very deficient were25.93%and72.59%(below class4), respectively. The soil available Cu, available Fe and available B were sufficient, the ratio of higher than class3was100%.2. From the soil absorption experiment results, we could conclude that the ratio of K absorption by soil was50.22%, and we recommended that68.14μg/ml K was proper used in potted plants. Recommendation of potted plants best treatment did not need to add P. The ratio of Zn absorption by soil in Fangqiang Farm was80.02%, and the recommendation quantity of Zn was5.6μg/ml. The soil needed to add60μg/ml Mn to balance the fixation of Mn. The ratio of Cu absorption by soil was80.40%, and we recommended that15.86μg/ml Cu was proper used in potted plants. The soil in Fangqiang Farm had a strong absorption on K, Zn, Mn and Cu, but had a weak absorption on P. Thus, people should pay attention to combined application of these elements when fertilize.3. By pot experiment, we could conclude that adding N to soil in Fangqiang Farm could increase the productivity of corn and rice obviously. Through this we knew that nitrogen was necessary in soil fertilizers. Adding P could not increase the productivity obviously. Adding K could not increase the productivity obviously, which result was the same as that by soil test. If possible, adding a little K could increase the quality of the crops. Treatments without Cu, Zn and Mn had different impacts to some extent. In conclusion, the main limiting factors of soil nutrients were Mn, Zn, Cu, N, K and P.4. The preliminary determination on soil nutrients limiting factors by the first three steps of Systematic Research of Soil Nutrient Status which include chemical analysis, absorption experiment and pot experiment had been confirmed by field experiment. And this result was worth promoting at a large scale in that region.5. In this research, we could conclude that the main limiting factors of rice production in Fangqiang Farm were Mn and Zn, and no adding of those elements leaded to the reduction of the output significantly. Second factors were K and N, and no adding of those elements also decreased the output. While some elements, such as Cu, were potential limiting factors. Thus, We should not only pay attention to using the N, P and K, but also to reasonably fertilizing the micro-elements fertilizer in future. |
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