Construction And Evaluation Of Soil Health Index System In Citrus Orchard

Soil is the foundation of agroecosystems,and an accurate grasp of its health status and change patterns is of great significance for achieving the sustainable development.In the past,soil health evaluation failed to pay sufficient attention to biological indexes.The starting point for the investigation of the soil status by the Ministry of Natural Resources,the Ministry of Agriculture and Rural Affairs,the Ministry of the Ministry of Ecological Environment was inconsistent,resulting in different focuses of the existing evaluation systems.The diversity of evaluation index and evaluation methods used for different crops made it difficult to achieve a comprehensive evaluation of soil health status.Therefore,based on domestic and international soil health evaluation research,this paper primarily established a set of soil health evaluation system suitable for citrus planting,multi-objective coordination and multi-dimensional monitoring by taking 60 citrus orchards in Hubei Province as objects,and then combined the single pollution index,Nemero comprehensive pollution index and fuzzy mathematical comprehensive evaluation method to carry out soil health evaluation.In order to provide theoretical basis and data support for the cultivation management,fertilization,regulation of soil health and improvement of fruit quality in citrus orchards.The main conclusions of this paper are as follows:(1)The evaluation system of soil health of citrus orchards was established.The evaluation indexes were divided into basic indexes and limiting indexes to construct an index system suitable for soil health evaluation of citrus orchard.The basic indexes included soil bulk density,soil texture,p H,organic matter,alkaline nitrogen,available phosphorus,fast-acting potassium,available iron,available manganese,available copper,available zinc,exchangeable magnesium,exchangeable calcium,available boron,available selenium,microbial carbon and soil-borne diseases.The limiting indexes included As,Cr,Cd,Pb and Hg heavy metal elements.The index weights were determined based on the expert scoring method and the coefficient of variation method.The soil environmental quality was evaluated using the single pollution index method and the Nemero comprehensive pollution index method,if the Nemero comprehensive pollution index of the tested soil reached more than mildly polluted,the soil was considered unhealthy.Conversely,the fuzzy mathematical comprehensive evaluation method was used to evaluate the soil health.(2)The soil characteristics of the test citrus orchards in the study area were defined.The bulk density of the tested soil ranged from 1.21 to 1.29 g/cm~3,with 51.67%and48.33%being suitable and slightly compacted.Soil textures were clay,chalky clay,chalky clay loam,chalky loam and chalky loam.Soil p H ranged from 4.35 to 6.49,with Yidu City and Dangyang City being acidic and at risk of acidification.Soil organic matter ranged from 14.16 to 24.36 g/kg was lacking in Yidu City and Danyang City,while all other soils were in the optimum growth range.Nitrogen,phosphorus and potassium are suitable or high to meet the needs of citrus growth.The content of exchangeable calcium in soil of Zhanghe New District and exchangeable magnesium in soil of Xiaoting District,Zhijiang City and Zhanghe New District is in the appropriate range.All the test citrus orchards were extremely low in effective selenium,while effective iron and effective manganese were high overall.The soil effective boron in Yidu City and the soil effective copper,zinc and boron in Danyang City were lacking.The soil microbial carbon content of the test citrus orchards ranged from 99.38 to286.13 mg/kg,with Zigui County being significantly higher than that of Zhijiang City and Zhanghe New District.Soil-borne diseases were mainly foot rot and root rot.The diversity of soil fungi community in Zhijiang City was richer than that in Zhanghe New District and the diversity of soil bacteria community was richer than that in Zigui County.(3)The health status of the tested citrus orchard soils was evaluated.According to the evaluation of soil heavy metal pollution,there were exceedances of Cr,As and Cd in the test citrus orchards(5.00%,1.67%and 1.67%respectively higher).There was no heavy contamination in the single pollution index of the sampled orchards,but only moderate and mild pollution caused by Cr,As and Cd.The proportion of mildly and moderately polluted soil with Cr was 1.670%and 3.330%,and the proportion of mildly polluted soil with As and Cd was 1.670%.Mildly and moderately polluted soil by Cr and Cd were distributed in Zigui County,and mild As pollution was distributed in Yidu City.The Nemero comprehensive pollution index of 8.330%sampled citrus orchard soil exceeded the warning line.The soil health of the tested citrus orchards in the study area was good,concentrated in healthy,sub-healthy and unhealthy states,with 58.33%,40.00%and 1.670%respectively.(4)The correlation between the soil health comprehensive index and citrus yield and fruit quality was analyzed.There was a positively linear correlation between citrus productivity and the soil health comprehensive index(R~2=0.57).The titratable acid content of the fruits was linearly and negatively correlated with the soil health comprehensive index(R~2=0.56).The citrus single fruit weight,edibility rate,TSS,VC and acid fixation ratio were linearly and positively correlated with the soil health comprehensive index respectively(R~2=0.57,0.65,0.66,0.66 and 0.84).The higher the soil health comprehensive index,the better citrus productivity and quality.It was proved that the index system and evaluation method constructed in this study were scientific and reasonable,which could better reflect the health condition of the tested citrus orchard soils.