| Over the past few decades,fertilizer application has played an important role in maintaining the food demand of the growing population.However,with the overuse or misuse of chemical fertilizer,a large area of farmland soil has been degraded(such as acidification and salinization),which also brings a series of environmental problems.In order to maintain sustainable development of agriculture and improve soil quality,it has become an urgent need for agricultural production to reduce fertilizer input,improve nutrient use efficiency and maintain sustainable productivity of soil through nutrient optimization management.In recent years,more and more attention has been paid to the use of organic fertilizer to improve soil fertility,which can not only replace part of chemical fertilizer to reduce the negative impact of chemical fertilizer,but also effectively utilize organic waste.In this study,based on the condition of equal nutrients,two typical rice-wheat and rice-rape rotation systems in Jiangsu Province were selected to study the effects of two different types of organic fertilizer substitution(rice-wheat rotation systems in Northern Jiangsu)of commercial organic fertilizer and vermicompost organic fertilizer,and two different substitution ratios of 20% and 40%of commercial organic fertilizer(rice-rape systems in southern Jiangsu)on soil fertility and crop nutrient utilization.The results can provide scientific guidance for the restoration and improvement of rice field quality,rice field management and precision fertilization in different regions of Jiangsu Province.The main results are as follows:In the experiment of rice-wheat rotation system,compared with the total fertilizer treatment,the commercial organic fertilizer replaces 40% fertilizer and vermicular manure organic fertilizer instead of 40% fertilizer,which significantly increases soil organic matter,total nitrogen and microbial biomass carbon,with an increase of 4.85%-132.07%,there was no significant difference in soil properties between the two treatments.Compared with the total amount of fertilizer,organic fertilizer replaced some fertilizer significantly increased the activities of extracellular enzymes related to carbon,nitrogen and phosphorus cycle in rice-wheat rotation soil,with an increase of15.02%-65.94%.Vermicompost organic fertilizer replacement significantly increased the activities of extracellular enzymes in wheat crop soil in 2020.The replacement of40% fertilizer with vermicompost manure significantly increased the PLFA content of actinomycete and PLFA of Gram-positive bacteria in paddy field.In terms of crop yield,compared with the total fertilizer treatment,organic fertilizer instead of partial fertilizer treatment increased and rice-wheat annual yield,with an increase of 13.69%-26.44%,respectively,the effect of replacing organic fertilizer with vermicompost is better.Compared with the total fertilizer treatment,the organic fertilizer replacement treatment significantly increased the accumulation of nitrogen,phosphorus and potassium in the upper part of the rice and wheat plants,and increased the contribution rate,agricultural efficiency,partial productivity and utilization rate of phosphorus fertilizer.The results showed that crop yield,soil extracellular enzyme activity,microbial properties and community structure were positively correlated with soil properties such as organic matter and total nitrogen.Soil total nitrogen was the main factor driving the change of PLFA community in rice season.In the experiment of rice-rape rotation system,organic fertilizer replaced 20%fertilizer and 40% fertilizer instead of 40% fertilizer,which increased soil organic matter,total nitrogen,total phosphorus and available nutrient in varying degrees,with an increase of 13.25%-62.50%.Soil microbial biomass,carbon,nitrogen and soil respiration also increased significantly in the replacement treatment of organic fertilizer,especially the 40% of organic fertilizer.Compared with the total amount of fertilizer,organic fertilizer replaced some fertilizers significantly increased the activities of carbon nitrogen and phosphorus cycle related extracellular enzymes,such as β-glucosidase,cellulase,xylanase,leucine aminopeptidase,N-acetyl-β-d-glucosidase and acid phosphatase,increased by 20.33%-140.31% in rape season,but only xylanase activity increased significantly in rice season,with an increase of 133.63%-159.86%.The results showed that the organic fertilizer replacement of 40% fertilizer significantly increased the total PLFA,bacterial PLFA and fungi PLFA in rice season,with an increase of 28.87%-47.07%,while the effect of organic fertilizer replacement of 20%fertilizer on the PLFA index of soil was no significant difference with that of total fertilizer treatment.In terms of crop yield,organic fertilizer replacement fertilizer treatment increased and rice-rape annual yield,with an increase of 12.64%-15.86%,the effect of organic fertilizer instead of 40% is better.The accumulation of nitrogen,phosphorus and potassium in the upper part of rape and rice plants was increased by18.16%-106.52% in the treatment of organic fertilizer instead of total fertilizer.In terms of nutrient use efficiency,only 40% of chemical fertilizer was replaced by organic fertilizer to increase potassium use efficiency of rice.Correlation analysis showed that crop yield,soil extracellular enzyme activity,microbial properties and community structure were significantly positively correlated with soil properties such as organic matter and total nitrogen.Soil organic matter was the main factor driving the change of soil PLFA community in rice season. |
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