| Based on the long-term fertilization experiment on Heilu soil in northweast of China to investigate the evolution regulation of soil fertility and crop yields under different fertilization,the relationship between soil fertility and crop yields and soil organic carbon sequestration mechanism fixation.The results showed that the crop yields,soil organic carbon and total nitrogen contents could be increased by long-term balanced application of chemical fertilizer,straw return combined with chemical fertilizer,organic fertilizer and organic fertilizer combined with chemical fertilizer.The yield increase of wheat was significantly greater than that of corn.The cumulative yield can eliminate the inter-annual crop yield fluctuation on a longer time scale,and by establishing the relationship between planting years and cumulative yield,the parameters such as average crop yield,yield evolution trend and crop yield contribution of fertilizers under different fertilization treatments can be accurately determined.Soil fertility level affects the crop yield contribution of fertilizer,the yield contribution of nitrogen fertilizer and phosphate fertilizer of corn with the planting years show a quadratic concave function and convex function relationship,respectively,the annual yield contribution of organic fertilizer treated by M and MNP is 3533,1896 kg·hm-2,and that of wheat is 1492,744 kg·hm-2.The annual yield contributions of corn and wheat were 429 and 206 kg·hm-2 respectively.In the wheat/maize rotation system in the Heilu soil area of the loess plateau,the long-term straw mulching,application of organic fertilizer and the combination of organic fertilizer and chemical fertilizer increased the crop yield compared with conventional fertilization.Meanwhile,the soil organic matter and total nitrogen content were also improved and so the soil fertility quality was improved.Suitable fertilizer application rate is N 90 kg·hm-2,P2O5 75 kg·hm-2.If the straw return to the field,the phosphorus(P2O5)application rate was 75 kg·hm-2 biannual.The organic matter and total nitrogen contents in soil were significantly positively correlated.Every 1g·kg-1 increase in soil organic matter content,the increase of soil total nitrogen content was 0.028g·kg-1.For every 1g·kg-1 increase of total nitrogen in soil,the increase of corn and wheat grain yield reached 12175 kg·hm-2 and 6507 kg·hm-2,respectively.So it is great significance of soil total nitrogen content for increase crop yield.Input 1 ton organic carbon per hectare in SNP treatment soil organic carbon content increased by 0.06 g kg-1,soil organic carbon sequestration rate is 15%,however CK,N,NP,M and MNP increase rates was 0.12-0.15 g·kg-1,organic carbon soil sequestration rate was 34%—41%.Soil organic carbon sequestration rate and organic carbon inputs and its quality has a close relationship,low organic carbon inputs,sequestration rate is high,while the inputs is high,the sequestration rate is low.High degree of humification of organic matter in soil sequestration rate is high.There was a significant positive correlation between total nitrogen content and maize and wheat yield.Maize yield increased with the increase of soil organic carbon content,but wheat yield increased rapidly with the increase of soil organic carbon content at first,and then stabilized,with an inflection point value of 11.8 g·kg-1.The organic carbon content of soil in the 0-60cm soil layer could be increased by applying organic fertilizer and the combination of organic manure and chemical fertilizer.The organic carbon content in the soil layer of below 60cm was not significantly changed compared with that in the control,while the organic carbon content in the soil layer below 60cm could be significantly increased by straw return.With the increase of soil depth,the organic carbon content of soil decreased firstly and then increased.The proportion of bound organic carbon to soil total organic carbon between different fertilization treatments ranged from 85.65%to 93.07%,while the proportion of free organic carbon to soil total organic carbon ranged from 7.15%to 14.34%,the content of bound organic carbon was 11.12-6.49 times that of free organic carbon.Long-term fertilization of organic fertilizer not only significantly increased the free organic carbon in the cultivated soil,free organic carbon in M and MNP treatment increased by 79.89%and 29.37%respectively compared with CK.Long-term application of organicm anure(M and MNP)and straw return combination chemical fertilizer(SNP)significantly increased the loosely combined organic carbon content of tillage layer(0-20cm),which increased by 194%,149%and 165%,respectively,and the organic carbon content in the stablely combined increased by 125.87%,58.12%and 95%,respectively,compared with the control.However,the application of organic manure has no significant effect on the tightly combined organic carbon content in 0-20cm soil layer.Long-term application of organic fertilizer combined with nitrogen and phosphorus,or straw return combined with nitrogen and phosphorus chemical fertilizer not only can generally increase the number of macro aggregates in soil and the number of small aggregates,but also the organic carbon content in large aggregates,small aggregates and micro aggregates also increased significantly compared with the control.The proportion of organic carbon in large aggregates in soil organic carbon ranged from 34.79%to 38.94%,that in small aggregates ranged from 26.40%to 35.05%,and that in micro aggregates ranged from 19.80%to 28.57%.The proportion of organic carbon in soil is the highest in large aggregates.The content of soil organic carbon increased with the increase of large water stable aggregates and small water stable aggregates.According to the calculation using the one-variable linear model,if the number of macro water-stable aggregates increases by 1 percentage point,the soil organic carbon content can increase by 0.39g·kg-1,and if the number of small aggregates increases by 1 percentage point,the soil organic carbon content can increase by 0.66g·kg-1,and contribution of small water stable aggregates to soil organic carbon was slightly higher than that of large water stable aggregates.The average mass diameter of soil increased by 1cm,the soil organic carbon content increased by 14.93 g·kg-1.Soil organic carbon content with different size of aggregate organic carbon content increase is increased,the increment of soil organic carbon(1.15g·kg-1)caused by the organic carbon content of microaggregates was greater than that of small aggregates(0.98g·kg-1),small aggregates are slightly larger than large aggregates(0.95 g·kg-1).Thus,the smaller the aggregate has the greater sequestration capacity of organic carbon.Soil silty complex content>>clay complex content>sand complex content.Organic manure(M),organic manure combination with chemical fertilizer NPK(MNP)and straw return with and fertilizer NPK(SNP)applying significantly increased sand complex content than control,moreover organic carbon content in sand complex,silty complex and clay complex is also increased significantly in these treatments.Fertilization significantly increased the proportion of organic carbon in the sand complex to soil organic carbon.if the organic carbon content in the sand complex increased by 1 g·kg-1,the soil organic carbon content increased by 3.72 g.kg-1,while clay complexs produced increase was 3.27 g·kg-1,but the clay complex content was significantly higher than that of the sand complex,so the clay complex was the main part of the soil organic carbon fixation. |
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