Effects Of Organic Fertilizer Substitution Of Chemical Fertilizer On Crop Yield And Soil Microbial Flora Under The Maize-cabbage-potato Rotation Model

Fertilization is essential to increase soil fertility and increase crop yields.The widespread application of chemical fertilizers has made a huge contribution to ensure the food production in China,but excessive use of chemical fertilizers can cause many problems such as soil acidification,degradation and environmental pollution.The application of organic fertilizer and bio-organic fertilizer is conducive to improving soil quality,enhancing plant absorption of nutrients,protecting plants from pathogen infection,and promoting crop growth.Trichoderma guizhouense NJAU4742 is a kind of beneficial fungus which was screened by this research group and showed a significant ability to promote plant growth and to control soil-borne diseases.However,the field effect of long-term application of organic fertilizers partly replacing of chemical fertilizers still needs further study.In this experiment,five treatments were set up in the long-term field test site in Guangming Village,Nantong City,Jiangsu Province,namely:（1）applying chemical fertilizer（CF）;（2）Organic fertilizer replacing 15%chemical fertilizer nitrogen（OF15%）;（3）Organic fertilizer replacing 30%chemical fertilizer nitrogen（OF30%）;（4）Bio-organic fertilizer replacing 15%chemical fertilizer nitrogen（BF15%）;（5）Bio-organic fertilizer replacing 30%chemical fertilizer nitrogen（BF30%）.In the six-season crops in two-round of corn-cabbage-potato rotation system,the effects of continuous fertilizer application on crop yield and soil microbial flora were explored.The main findings are as following:1.Compared with chemical fertilizers,organic fertilizer and bio-organic fertilizer replacement（15%and 30%chemical fertilizer N）all increased the yield of crops in corn-cabbage-potato rotation system.Among them,organic fertilizer replacement 15%and30%chemical fertilizer N treatments had an obviously effect on corn yield.The organic fertilizer replacements of 30%chemical fertilizer N treatment with organic fertilizer and bio-organic fertilizer had a significant increase in potato yield respectively.In the corn-cabbage-potato rotation system,most of the soil nutrients are significantly higher in the potato season than in other seasons.Compared with chemical fertilizers,organic fertilizer and bio-organic fertilizer replacement treatments both increase soil AP,AK,NH₄⁺-N,NO₃^--N,p H,and OM contents.The replacement of 30%chemical fertilizer N by organic fertilizer and bio-organic fertilizer has significant effects on soil nutrient improvement respectively.Bio-organic fertilizer substitution has a better effect on soil nutrient increase than organic fertilizer replacement.In addition,AK,NH₄⁺-N,NO₃^--N,p H,EC and OM in the soil are significantly positively correlated with crop yields.2.Since the replacement of 30%chemical fertilizer N by organic fertilizer and bio-organic fertilizer had the most significant impacts on the crop yield and soil physical and chemical properties in the potato season,the soils of the third and sixth potato seasons in treatments of chemical fertilizer,organic fertilizer and bio-organic fertilizer replacing30%of chemical fertilizer N were selected.Through the Mi Seq high-throughput sequencing technology was used to further explore the impact of organic fertilizer and bio-organic fertilizer replacement treatment on the soil microbial flora.The results show that the soil bacterial community structure is regulated by fertilizers,planting season and soil nutrients.Compared with chemical fertilizers,organic fertilizer and bio-organic fertilizer 30%substitution treatment all increase the abundance and diversity of bacterial communities and the effect becomes more obvious with the increase of planting seasons.The replacement of 30%treatment with organic fertilizer and bio-organic fertilizer can significantly increase the relative abundance of some bacterial genus such as Bacillus,Salinimicrobium,Brevundimonas and Sulfuritalea,that are positively related to yield increase significantly.The function prediction results of bacterial community showed that organic fertilizer and bio-organic fertilizer replacement treatments had stronger functions related to nitrogen and carbon cycles than chemical fertilizer treatments.3.In terms of fungal community structure,the soil fungal community is mainly affected by the combined effects of fertilization and soil nutrients.Compared with chemical fertilizers,organic fertilizer replacement and bio-organic fertilizer replacement treatments increased the abundance and diversity of fungal communities.Soil fungal communities in bio-organic fertilizer replacement treatment（30%）was more affected by soil nutrients.The replacement of 30%chemical fertilizer N by organic fertilizer or bio-organic fertilizer significantly increased the relative abundance of key fungi groups such as Fusarium equiseti,Fusarium falciforme,Donkioporia and Bjerkandera that are significantly positively correlated with yield.In addition,the function prediction results of fungal community showed that,compared with chemical fertilizers,organic fertilizer and bio-organic fertilizer replacement treatments significantly increase the relative abundance of functional groups such as Dung Saprotroph,which are beneficial to plant growth,and reduces the relative abundance of functional groups such as Animal Pathogen,which are harmful to plant growth,and this effect becames more obvious as the rotation season increases.In summary,the partial replacement of chemical fertilizers with organic fertilizers and bio-organic fertilizers could improve soil physical and chemical properties,increased the contents of available nutrients in the soil,improved the structure of soil microbial communities,increased the richness and diversity of soil microbial communities,and increased the relative abundance of key microbial groups,which were significantly and positively related to crop yield,all of which promoted the increase of crop yields in the corn-cabbage-potato rotation system.Comprehensively,the effect of organic fertilizer replacing or bio-organic fertilizer replacing 30%chemical fertilizer N on soil fertilization and microbial flora is better than 15%replacement treatment,which is a advised fertilization pattern to realize the rational utilization of fertilizer resources,improve the soil environment and crop yields.