Effects Of Long-term Application Of Organic Fertilizer On The Health Of Paddy Soi

The reduction of chemical fertilizers and the application of organic fertilizers is a scientific and effective fertilization measure to improve soil structure,improve soil fertility,and enhance soil sustainability.It is of great significance for improving crop yield and maintaining sustainable soil development.In recent years,soil health has become a research hotspot in soil academia.In agricultural production,evaluating soil health can be used as a basis for adjusting and improving farmland management.In this study,the soil and rice in southern paddy fields were taken as the research objects,and the effect of organic fertilizer application on soil physical properties,chemical properties,biological properties,risk of heavy metal pollution and rice quality was studied based on a 7-year located field experiment of organic fertilizer application.Analyze the correlation between the indicators,screen the appropriate evaluation indicators,and use the principal component analysis（PCA）method to evaluate the soil health status,and then describe the response of soil health to the combined application of organic and inorganic fertilizers.Five treatments were set in the location test,namely no fertilization（CK）,single application of chemical fertilizer（CF）,and chemical fertilizer reduction combined with 2250 kg/hm²（M1）,4500 kg/hm²（M2）and 9000 kg/hm²（M3）three treatments.The main findings are as follows:（1）The application of organic fertilizers significantly reduced soil bulk density,increased soil total porosity,and increased field water holding capacity.Compared with CF,soil bulk density in M1,M2 and M3 treatments decreased by 10.14%,7.14%and 4.85%,respectively,and the total soil porosity increased by 3.10%,5.40%and6.20%,respectively.The application of organic fertilizer significantly increased the proportion of soil aggregates with a particle size of>0.25 mm,and decreased the proportion of aggregates with a particle size of 0.053 mm to 0.25 mm.Compared with CF,the proportions of soil aggregates with a particle size of>2 mm in M1,M2 and M3 increased by 4.82%,13.64%and 24.86%,respectively,and the proportions of soil aggregates with a particle size of 0.25mm to 2 mm in M1,M2 and M3 increased by9.50%,10.30%and 15.79%,respectively,and the proportions of 0.053mm～0.25mm particle size microaggregates decreased by 0.22%,30.60%and 49.96%,respectively.The application of organic fertilizer increased the proportion of soil macroaggregates and enhanced the water stability of macroaggregates.The distribution of soil macroaggregates and the proportion of water-stable aggregates were the largest in M3treatment,which were 90.59%and 67.12%,respectively.（2）Combined application of organic and inorganic fertilizers significantly increased soil p H,organic matter,total nitrogen,alkali-hydrolyzed nitrogen,total phosphorus,available phosphorus,available potassium,high laible organic matter（HLOM）,medium laible organic matter（MLOM）,laible organic matter（LOM）,easy oxidation Organic carbon（EOC）,dissolved organic carbon（DOC）and microbial biomass carbon（MBC）contents.The combined application of organic and inorganic fertilizers improved the soil carbon pool index and carbon pool activity.The carbon pool management indexes of CF,M1,M2,and M3 soil active organic matter were 115,118,133,and 150,respectively.The soil nitrogen mineralization reached its peak in the first week of cultivation.After the end of cultivation,the accumulated nitrogen mineralization of CK,CF,M1,M2 and M3 treatments were 11.76 mg·kg-1、13.46mg·kg-1、and 14.86 mg·kg^-1、15.03 mg·kg^-1and 17.80 mg·kg^-1,combined application of organic and inorganic fertilizers promoted soil nitrogen mineralization.The combination of organic and inorganic applications promoted soil nitrogen mineralization.（3）The combination of organic and inorganic applications significantly enhanced the activities of soil microorganisms,urease,catalase,peroxidase and phenoloxidase,increased the number of soil bacteria-eating nematodes,omnivorous/predatory nematodes and herbivorous nematodes,and improved the diversity of soil nematodes Shannon Sex Index,Evenness Index,Simpson Index and Wasleska Index.The ratio of beneficial nematodes to harmful nematodes in M1,M2and M3 treatments was increased by 9.80%,24.02%and 16.18%,respectively,compared with CF.The soil microbial carbon dioxide production rate of M2 treatment was the highest,the activities of urease,peroxidase and polyphenol oxidase were the strongest,and the number of soil bacteria-eating nematodes,omnivorous/predatory nematodes and herbivorous nematodes was the largest.（4）The combined application of organic and inorganic fertilizers improved the yield and quality of rice,and the M2 treatment had the highest yield and the best quality of rice.（5）The combined application of organic and inorganic fertilizers significantly increased the accumulation of heavy metals Cu,Zn and Cd in soil,increased the available content of soil Cu,Zn,Pb,Cd and As,and promoted the absorption of heavy metals Cd,As,Cu and Zn by rice.The single-factor index method and Nemerow were used to evaluate the accumulation risk of heavy metals in the soil.The soils of CK,CF,M1,and M2 were all clean soils and were not polluted by heavy metals.The single heavy metal pollution index of Cu in the M3 soil was 1.121,which had been polluted by the soil heavy metal Cu.The heavy metal content of rice is within the food pollution limit,and it is not contaminated by heavy metals.（6）The principal component analysis method was used to evaluate the soil physical properties,chemical properties,biological properties and the comprehensive status of soil health.The comprehensive score of soil physical and chemical properties of M3 treatment was the highest,the comprehensive score of soil biological properties of M2 treatment was the highest,and the comprehensive evaluation score of soil health of M3 treatment was the highest.In summary,the combined application of organic and inorganic fertilizers can improve soil structure,increase soil fertility,enhance soil biological activity,improve rice yield and quality,and improve soil health.The combined application of organic and inorganic fertilizers promoted the accumulation of some heavy metals in the soil and rice,but the soil and rice were not clean under the appropriate amount of organic fertilizer application.Considering the soil health evaluation score,soil biological activity,rice yield and quality,and accumulation of heavy metals,chemical fertilizer reduction combined with 4500 kg/hm2 organic fertilizer was the best combined application amount of organic fertilizer in local paddy fields.