| The inherent soil productivity is the ability to support crop production and provide a variety of ecological services.It is a comprehensive reflection of the physical properties,chemical properties and biological characteristics of soil,and the inherent soil productivity is evaluated by crop yield under the condition of non-fertilization.It determines soil productivity with water and fertilizer effect and field management.Though the land in China is vast,the area of cultivatable land is limited.2/3 of the cultivated land in China is still at the middle and low yield level,which is very unfavorable for agricultural production and food security in China.In the current situation,it is not practical to improve grain production capacity through increasing the area of cultivation.Only improving the soil productivity of the existing cultivated land is the necessary way for China to realize―storing grain in land‖.Scientific and feasible recommendation on regional fertilization is a necessary means for China to realize―storing grain with technology‖.Based on the results of"3414"test of Chongqing rice and maize,the soil data and fertilization survey results in different periods,this paper comprehensively analyzed the changes of inherent soil productivity and soil nutrient content in the last 30 years.and the effects of inherent soil productivity on nutrient uptake,yield and stability and sustainability of crops were explored.Finally,we try to use the soil inherent productivity as the fertilization index to explore the feasibility of this indicator on the fertilization guidance of rice and maize in Chongqing,and compare with other classical fertilization methods.The main findings are as follows:1、Chongqing paddy field inherent soil productivity has been significantly improved in the last 30 years,the increased range in dry land soil fertility is higher than that in paddy field in Chongqing.In the last 30 years,the content of soil organic matter,total N,available N and available P increased significantly.soil organic matter increased by 1.7g·kg-1,and dry land increased by 2.5 g kg-1,which is larger than that of paddy field 1.0 g kg-1,but the organic matter content in dryland is still lower than that in paddy field,but the gap between the two has become closer,Soil organic matter content is moving towards homogenization.The soil pH of Chongqing decreased significantly,The pH has decreased by an average of 0.5 in the last 30 years,which declined from neutral 6.7 to slightly acidic 6.2.The soil pH in dryland was still higher than that in paddy field,but the gap was narrowing.The average content of Mg,Fe,Mn,Cu and Zn in Chongqing soil is high,and the nutrient supply is sufficient,but the average content of B is at a relatively low level,and some areas are close to the lack of level,need to be added in time.Chongqing soil inherent productivity evaluation shows that the proportion of the high part is low,especially the dry land,elevation and soil thickness are the main reasons that affect the grade of cultivated land in Chongqing,But in addition,The impact on the level of soil inherent productivity on the southeast and northeast of Chongqing is also very significant.from 1980s to 2010s,chemical fertilizer of Chongqing cultivated land input increased.Organic fertilizer input decreased,nitrogen surplus narrowed,nutrient output increased,nitrogen surplus narrowed,phosphorus is from deficit to surplus,and potassium is from surplus to deficit.The increase of nitrogen and phosphorus surplus in Chongqing and the expansion of the deficit of potash fertilizer are the main reasons for the increase of available nitrogen and available phosphorus and the decrease of available potassium in Chongqing.The improvement of soil inherent productivity in Chongqing is due to the increase of soil available N,available P and organic matter.2、The increase of inherent soil productivity can promote the supply of soil nutrients and crop absorption,On the precondition of soil inherent soil improvement,it will reduce the utilization efficiency of fertilizer nutrient unless reducing fertilizer use,Therefore controlling the input of fertilizer under high soil inherent productivity can improve the nutrient use efficiency of fertilizers.The utilization efficiency of nitrogen nutrient in inherent soil productivity is stronger than phosphorus and potassium.3、The present average yield of the soil inherent productivity of paddy soil is 6.0t·hm-2 in Chongqing,the inherent soil productivity contribution rate is 72%,The average yield of the soil inherent productivity of dry land is 4.0 t·hm-2,the inherent soil productivity contribution rate is 57%,the contribution of cultivated land soil inherent productivity to yield is more than fertilizer.There was a significant positive correlation between the base soil yield and the relative contribution rate of soil inherent productivity,and there was a significant negative correlation between Fertilizer Relative Contribution Rate and Inherent soil productivity,highly cultivated land can replace the contribution of fertilizer to yield and reduce fertilizer use.The soil inherent productivity contribution rate of rice in paddy field in Chongqing is higher than that in dry land,and the contribution rate of fertilizer in dryland maize is higher than that in paddy field.Nitrogen fertilizer is still the most nutrient production of fertilizer production,much higher than the phosphorus and potassium.There is a significant positive correlation between soil inherent productivity yield and fertilization yield of cultivated land.With the increase of soil inherent productivity yield,fertilization yield is also increasing.High soil inherent productivity levels can also be stable and sustainable at high yields,and drylands with a basement>4 t hm-2 have high stability and sustainability.There was a significant negative correlation between the contribution rate of N,P and K in cultivated soil and the yield of nitrogen and phosphorus,The effect of soil inherent productivity on the yield of chemical fertilizer was significant,Increased yield per unit of fertilizer in the soils of low soil inherent productivity levels are higher than those of high soil inherent productivity.4.The optimal economic benefits calculated with quadratic function are targeted yield.Fertilizer quantity for each"3414"tested spot is calculated with fertility subtraction,and the output with corresponding fertilizer quantity is simulated through a quadratic function formula.The result shows that the nitrogen and phosphorus fertilizer quantity calculated with soil fertility subtraction is close to the optimal fertilizer quantity calculation with quadratic function.What is more,the obtained output reaches over 95%of optimal economic yield.This can be used for recommendation on use of nitrogen and phosphorus fertilizers in most areas in Chongqing.However,the amount of potassium calculated with soil fertility subtraction is too high,which might cause a waste of nutrient resources.Therefore,it not suitable for potassium fertilizer recommendation on rice corn plantation in Chongqing.5.Through establishing relevant relation between nutrient contribution rate and fertilizer recommendation with soil fertility subtraction,establishing relevant relation between inherent soil productivity output as well as output in nutritional deficiency zone and nutrient contribution rate,output with inherent soil productivity,output in nutrient deficiency zone and output with recommended fertilizer under different nutrient contribution can be established.The nitrogen and phosphorus fertilizer use for rice and corn plantation in different areas in Chongqing can be guided.But the potassium fertilizer quantity and nutrient contribution rate are not significantly correlated.Potassium fertilizer recommendation according to inherent soil productivity indicators cannot be made.6.On total soil potassium,rapidly available potassium and inherent soil productivity yield,significantly correlation with relative yield and nutrient contribution rate cannot be established.Potassium fertilizer recommendation on rice and corn cannot be made.Inherent soil productivity cannot be used to direct potassium application.This indicates that different fertilization methods have different effects in different regions and it is difficult to have a same method.The promotion of fertilization technology needs to be demonstrated and tested in details. |
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