Effects Of Agricultural Measures On Soil Quality And Bacterial Community Of Red Soil Plow Layers In Dryland

The red soil area is located in one of the main grain producing areas in China.However,its inherent physical barrier factors and the unreasonable agronomic measures taken to farm in this land have led to the deterioration of soil quality,as well as low and unstable crop yields.Evaluating the effects of various agronomic procedures on the quality of the red soil plough layer in dryland has significant practical significance for the selection of regional agronomic processes.However,due to different research purposes and objects,there is no unified standard or index for soil quality evaluation.With the deepening of nuances in the study of soil quality,the evaluation of dryland red soil quality based on the existing physical and chemical factor indicators can neither truly nor objectively reflect the current state of dryland red soil.Therefore,the introduction of microbial characteristic indicators has important theoretical significance for enriching and developing soil health and cultivated land quality.In this study,we used high-throughput sequencing technology,canonical correspondence analysis,and principal component analysis to explore the characteristics of red soil properties,bacterial community structure,and diversity changes under different agronomic measures to analyze the main controlling factors of bacterial community structure differentiation.We conducted this study based on 13agronomic measures in 3 trials:the experiment of long-term fertilization and location(CK,NPK,OM,NPKM)in dryland red soil started in 1986,the experiment of planting system transformation(HSD,LBD,GJD)started in 2006,and the experiment of tillage and straw returning(RC,RSF,RSD,PC,PSF,PSD)started in 2015.Our study takes into consideration individual or optimal combination agronomic measures that affect the production potential of Jiangxi dryland red soil to multi-dimensionally evaluate of dryland red soil quality.With this data,we established the minimum data set index for dryland red soil quality evaluation,defined the threshold range for the minimum dataset metrics,established a relationship between soil quality and crop production potential,and proposed regional reasonable agronomic measures.We obtained following results:(1)The application of exogenous organic fertilizers significantly improved the quality of red soil in dryland.Agronomic measures such as NPKM,PSD,LBD reduced soil bulk density,thickened plough layer,increased aggregate stability,the amount of available soil nutrients,and biological fertility,and also improved the soil’s comprehensive fertility index.Among the 13 studied agricultural methods,soils treated with NPKM showed the highest physical,chemical,and comprehensive fertility indices,which were 0.82,0.78,and 0.82,respectively,soils treated with LBD had the highest biological fertility index(0.90),while the comprehensive fertility index of no fertilization(CK)and RCtreatment was only 0.16 and 0.20,respectively.Compared with straw mulching,straw burial in dryland red soil had a better effect on improving the quality of the plough layer.After citrus planting,human disturbance,and organic fertilizer input decreased,the bulk soil density increased,the plough layer became shallower,the soil enzyme activity decreased,and the biological fertility was low.These factors resulted in a soil comprehensive fertility index of only 0.29,which required supportive and sensible cultivation and fertilization measures.It is worth noting that after long-term application of OM and NPKM,there was a significant accumulation of phosphorus:available phosphorus increased by 6.38 and 6.64 times and total phosphorus increased by 2.64 times and 2.31 times,respectively,while the increase in total nitrogen and total potassium was small.(2)The addition of organic fertilizers improved the bacterial community structure and diversity,and changed the abundance of dominant bacteria in dryland red soil.The results of high-throughput sequencing showed that NPKM,OM,LBD,and PSD treatments significantly increased theα-diversity of dryland red soil bacterial community and changed theβ-diversity.However,theβ-diversity of bacterial communities treated by OM and NPKM had a convergence phenomenon.At the phylum level,20 bacterial species were detected in dryland red soil,among which Acidobacteria,Proteobacteria,Chloroflexis,Actinobacteria,and Gemmatimonadetes were the common dominant phyla(relative abundance>5%)across all the agronomic measures.At the genus level,21 species were detected,and Nitrospira,MND1,and Candidatus Solibacter were the common dominant genera.The relative abundance of dominant bacteria at the phylum and genus levels varied significantly under different agronomic treatments.(3)Improved physicochemical properties drives bacterial community structure differentiation in dryland red soil.Using canonical correspondence and stepwise regression analysis,we found that the composition of water-stable aggregates was the most important physical factor driving bacterial community structure,diversity,and differentiation of the dominant bacteria,followed by soil bulk density,in which water-stable aggregates at>2mm had a promoting effect,while the soil bulk density had an inhibitory effect.The effective soil weight of the plough layer had a significant effect on the relative abundance of dominant bacteria..In detail,bacterial community structure differentiation in dryland red soil was driven by available phosphorous,followed closely by soil organic carbon content.Soil organic carbon content was the main factor driving bacterial community diversity,then soil p H and total phosphorus.The main chemical factors for the variation of dominant bacteria were soil p H and alkaline nitrogen,followed by organic carbon content.(4)The minimum data set index and threshold range for dryland red soil quality evaluation was clarified,and the relationship between soil quality index and crop productivity was resolved.The quality of the plough layer of 13agronomic procedures was evaluated by using 3 methods,and results showed that the soil quality index of NPKM was the highest,while the soil quality index of CK and RC was at a lower level.To establish the minimum data set indicators for the quality evaluation of the dryland red soil plough layer,the principal component analysis method was used.We determined the value range of the following indices:thickness of plough layer,average weight diameter of aggregates,available potassium,organic carbon,p H,soil bulk density,and catalase activity.The value range of each index is:the thickness of the plough layer≥20.58 cm,the average weight diameter of the aggregates≥0.76 mm,the available potassium AK≥142.39 mg/kg,the organic carbon≥12.04 g/kg,p H 4.91～5.78,soil bulk density 1.14～1.26 g/cm~3,catalase activity≥5.41μM p-NP/(g/h).The relationship between soil quality index and crop yield under the 3evaluation methods was clarified:when the dryland red soil quality index increased by 0.1 unit,the yield of maize and peanut could be increased by 1.11-1.36 t/hm~2and0.35-0.51 t/hm~2,respectively.These results show that NPKM,PSD,and LBD are effective agronomic measures for improving red soil quality and crop yield in dryland.They can significantly improve the quality of dryland red soil plough layer and crop productivity,and can increase bacterial community diversity by improving the physicochemical properties that drive bacterial community structure and dominant bacterial differentiation.