| Fertilization was an important measure for stable and high yield of crops.Long-term single application or excessive application of chemical fertilizer resulted in deterioration of soil physical and chemical properties,reduced fertilizer utilization rate and decrease of crop yield,etc.,which seriously affected the comprehensive production capacity of soil.Organic fertilizer played an important role in improving soil structure,increasing soil fertility and improving crop yield.In order to reduce the amount of fertilizer application and reduce the pollution of fertilizer to soil and environment under the high yield of crops,Provided the strategy of replacing some fertilizer nutrients with organic fertilizer in China,that was to reduce fertilizer input and replace chemical fertilizer with organic fertilizer on the premise of ensuring high yield of crops.Soil with different fertility characters was formed under the long-term and fixed fertilization management mode.It was important to study the relationship between the substitution rate of organic fertilizer(SROF)and soil fertility by the long-term and fixed-site trails,which was one of the important ways to realize the zero growth target of fertilizer in China.By analyzing the dataset of a 32-years fertilization experiment on black soil in Gongzhuling long-term experiment site,the change characteristics of SROF under different organic fertilizer application rate was discussed based on crop nitrogen uptake and soil nitrogen supply-demand balance.The quantitative relationship between the SROF and the soil fertility was further explored,based on analysis of the evolution of SROF and the soil fertility,provided a theory foundation for optimal fertilization.1)The content of soil total nitrogen,available phosphorus and available potassium in soil organic carbon,total nitrogen,effective phosphorus and available potassium in fertilizer treatment were significantly decreased with time,and other changes were not significant.Soil organic carbon,total nitrogen,alkali-free nitrogen,total phosphorus,and available phosphorus in organic fertilizer were significantly or significantly increased,but the effect on soil potassium content was not significant.Continuous application of organic fertilizer is an important measure to improve soil fertility.2)Results showed that the crop yield increased gradually with the application of organic fertilizer,the yield of organic fertilizer was similar to that of NPK fertilizer through 32 years of continuous fertilization,even higher than that of NPK.It showed a significant positive correlation between SROF and years of fertilization,based on the crop nitrogen uptake(P<0.01),and the SROF under the application of manure with high quantity level(M2)could reach 100%after 29 years,which was higher than that with the application of manure with conventional level(M1).3)The correlation coefficient(R~2)of SROF under the application of manure with conventional and high quantity level(M1 and M2)reached 0.78 and 0.84(P<0.01)based on crop nitrogen uptake and soil nitrogen supply-demand balance,the root mean square error(RMSE)of SROF under the application of manure with conventional and high quantity level(M1 and M2)were 10.39%and 14.58%,respectively,based on the soil nitrogen supply-demand balance,which proved the validity of the method to calculate SROF based on the nitrogen uptake of crop.4)The results of correlation analysis,path analysis and progressive regression indicated that the content of SOC was the major stationed soil fertility factors determining the different SROF,it decided 70%variances of the SROF.The results showed that the content of SOC was increased significantly under the long-term application of manure with conventional and high quantity level(M1 and M2)in black soil(P<0.01);The SROF was significantly nonlinear with the content of SOC(P<0.01),the content of SOC was 24.89g/kg when the SROF approaches the maximum 95%. |
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