| Integrated farming and breeding mode in paddy field which is a typical green rice farming method,makes full use of rice resources,and rice and animals are mutually beneficial.In recent years,the area of integrated farming and breeding mode in my country has expanded rapidly,among which the area of rice-crayfish co-culture（RC）is nearly half,reaching 1.1×106 ha.Compared with the traditional planting rice mode,the rice-crayfish（RC）co-culture mode introduced crayfish farming in the rice field.To meet the growth needs of the crayfish,firstly,a ring-shaped ditch was dug around the rice field to provide a rest for the crayfish.In the non-paddy season,the paddy field was flooded to raise crayfish.At the same time,the amount of organic matter（feeding,straw returning）was increased,and field engineering and agronomic measures were greatly changed,which affected the physicochemical properties of the paddy soil changes.However,a ring-shaped ditch in paddy fields and the flooding in non-rice season have significantly different effects on paddy fields with different land resource characteristics.We put forward the hypothesis:（i）the RC co-cultivation model is carried out in well-drained paddy field,due to the long-term flooding treatment,the soil reduction reaction was intense and the soil quality of the paddy fields decreases;（ii）carry out the RC co-cultivation mode in the cold waterlogged paddy field,and the ring-shaped ditch plays the role of deep ditch raising the field,which improves the soil quality of the cold waterlogged land.This study was conducted in Qianjiang City,Hubei Province from 2016 to 2017,and carried out two aspects of experimental research around the RC model.（1）Under the background of clear characteristics of different land resources,the RC co-culture model carried out the redox characteristics of the soil profile,and explored the effect of the RC model on the soil active organic carbon pool and the distribution of soil water-stable aggregate organic carbon in cold waterlogged fields,and the driving mechanism of soil organic carbon.（2）A field control experiment:from 2016to 2017 year,it was carried out at the graduate work station base,which used non-straw and non-feed（NN）,non-straw and feed（NF）,straw and feed（SF）,and straw and non-feed（SN）as the research objects.The conventional rice monoculture with straw return（CK-1）and without straw（CK-2）as a control,to prove the effect of straw returning and feed on the physicochemical properties,active organic carbon pool,water-stable organic carbon distribution of the tillage layer（0～20 cm）and the yield of rice and crayfish of the RC.The main findings are as follows:（1）The basic physicochemical properties of the soil profile in the RC co-cultivation model in well-drained paddy fields have changed,soil fertility has decreased,and the soil profile has become gleized.The RC co-culture model was carried out in good paddy fields,and the soil p H showed a trend of first increasing and then decreasing with the years of RC farming.The soil bulk density（BD）value increases with the increase of RC farming years,and compaction occurs.The soil cation exchange capacity（CEC）decreased with the increase of the RC co-cropping years.Compared with Y0 treatment,Y10,Y6 and Y2treatment soil profile accumulated a large amount of total reducing matter（TRM）,active reducing matter（ARM）,Fe（II）and Mn（II）.As the number of years of RC farming in paddy fields increases,the accumulated number increases.The soil oxidation-reduction potential（Eh）value of the RC model decreased significantly,and the soil profile Eh of Y10 and Y6treatments was less than 100 mv.The study of soil profile structure found that the gleization of RC co-culture model soil occurred in well-drained paddy fields,and the degree of gleization deepened as the years of RC co-culture increased.（2）The RC co-culture model was carried out in cold waterlogged fields,and decreased degree of soil gleization was obvious,and the soil structure and fertility of the rice fields were improved.In the cold waterlogging field,the RC co-culture mode was carried out,the soil p H value increased,the soil BD value decreased,the CEC concentration increased,and the soil fertility was improved.Compared with Y0 treatment,Y10,Y6 and Y2 treatment soil profiles have reduced concentrations of TRM,active reducing substances ARM,Fe（II）and Mn（II）.The soil Eh value increases with the increase of the RC co-culture period.With the increase of the RC co-culture years,the brown soil layer appeared in the soil profile of the cold waterlogged field due to the degree of soil gleization decreased.（3）Carried out the RC co-culture model in cold waterlogging fields,the amount of active organic carbon pool and the soil carbon pool management index（CPMI）in the soil profile of RC increased.In the RC fields,the easily oxidizable organic carbon（ROC）and particulate organic carbon（POC）in the soil active organic carbon pool increased significantly with the increase years of RC,and Y10 was significantly higher than Y0.In the 0～100 cm soil layer,CPMI value gradually increases with the increase of the RC years.The CPMI values of the Y10,Y6,Y2 and Y0 treatments are:201±57,198±111,149±47and 102±17 and the Y10 value was significantly higher than Y0.（4）The RC co-culture model which was carried out in cold waterlogged field can effectively promote the downward migration of fresh organic carbon in the soil profile and increase the SOC storage of the soil profile.The increase in soil profile SOC storage is mainly due to the fresh and unstable organic carbon storage in coarse aggregates（LM）,while the stable organic carbon storage in soil silt-clay aggregates（free-SC）and microaggregates（Mi）decreases.In the RC co-cultivation mode which was carried out in cold waterlogged field,the ROC and POC content in the soil active organic carbon pool increase,and the chemical protection of mineral-organic complexes formed by the complexation of inorganic minerals represented by Fep with active organic carbon plays an dominate role in soil organic carbon storage.（5）By establishing a minimum data set（MDS）and using a comprehensive evaluation method of soil quality indicators（SQI）to evaluate the soil quality of paddy soil in different treatments under cold waterlogged field,the SQI value was shown as:Y10>Y6>Y2>Y0.The MDS of SQI for RC fields were:SOC,TK,Eh,MBC and Mn（II）.The quality of the0～40 cm soil layer of the RC has been improved correspondingly with the increase of the RC years,which was manifested by the increase of nutrients such as SOC,TN,TP and TK.The comprehensive evaluation results of the soil quality in the RC showed that Mn（II）was significantly negatively correlated with the SQI,and the reducing substances in the soil represented by Mn（II）were obstacles to the sustainable production of the soil in the RC field under cold waterlogged field.（6）The soil p H value of the RC co-culture model was higher than that of the rice monoculture field for two years,from neutral to weak alkaline,and the annual soil Eh value is<-100 mv.Straw returning to the field and feeding treatment increased the source of nitrogen,resulting in the increase of NH4+-N and NO3--N content,and soil TN accumulation showed an increasing trend.Straw treatment increased the percentage of LM in the 0～20cm soil layer of the paddy field.After two years of experimentation,the percentage of small aggregates（SM）in soil treated with RC was the highest.Compared with the CK treatment,straw returning and feeding increased the content of POC,MBC and DOC.Feed significantly increased the yield of crayfish,and also showed a positive effect on rice yield,but did not reach a significant effect.Returning straw to the field showed positive and negative effects on the yield of crayfish and rice,respectively,but they did not reach significance.In summary,the transformation from traditional rice fields to RC farming on the Jianghan Plain has caused great changes in land use,which has a profound impact on the physicochemical properties of the paddy soil with different land resource characteristics.On the one hand,the RC co-culture model is carried out in the well-drained paddy field,due to the perennial flooding of the rice field,a large amount of reducing substances in the soil accumulate,and the degree of gleization of the soil profile is aggravated.On the other hand,the RC co-culture model was carried out in cold waterlogged fields.The ring-shaped ditch played a role of lowering the groundwater level in cold-leached fields.The increase of straw and feed and other materials in the soil increased the nutrient content of the soil.The amount of soil active organic carbon pool increases,the stability of water-stable aggregates is enhanced,and the quality of paddy soil is improved.Therefore,we first suggest that make full use of the waterlogged land in the Jianghan Plain,promote the RC model according to local conditions,rationally use land resources,and reduce the damage to the paddy soil caused by unreasonable development and utilization.Secondly,in the actual production management process,through scientific water management,agronomic measures such as sunning fields are carried out to improve soil oxygen content,and to achieve sustainable production of the soil in the RC. |
