Effects Of Combined Regulation Of Biochar And Tillage On Habitat Health And Crop Growth In Seasonal Frozen Soil Area

In recent years,agricultural resources,such as soil and water,have been under tremendous pressure due to the effects of our increasing population and food needs.To meet the needs of food production,the continuous reclamation and utilization of land and the use of pesticides and fertilizers have led to the degradation of the physical,chemical and biological structure of soil in the farmland ecosystem,which has seriously affected the farmland soil and water environment and crop growth,and threatened the function of the farmland ecosystem.In seasonal regions,the influence of the freeze-thaw cycle,farmland soil structure degradation and nutrient loss serious,combined with long-term irrational farming cause plough layer becomes shallow,and single farming methods,make the crop habitat in seasonal frozen health is affected by the serious,serious restricts the food production and the increase of people’s living standard in our country.With the occurrence of this phenomenon,deep tillage,as a way of conservation tillage,has been widely used in improving the ecological environment of farmland soil.In addition,biochar as a soil amendment has been widely studied by scholars at home and abroad,but most of them are carried out in temperate and non-cold regions,and there is still a lack of practical basis for regulating crop habitat health in seasonal frozen soil regions.Therefore,this study is based on the typical black soil area of Northeast China（Songnen Plain）and adopts the combined biochar-tillage control technology.Five different biochar application rates（0 kg/mu,250 kg/mu,500 kg/mu,750 kg/mu,1000 kg/mu,labeled CK,B25,B50,B75,B100）,two farming mode（shallow tillage,deep tillage,labeled ST,DT）were set respectively.By planting soybeans and maize crop,a total of 20 plot（soybean test area 10plot,maize test area 10 plot）,determination of soil structure,hot water dynamic,nutrient status and farmland soil environment related indicators,analyzing the soybean and maize growth indices under different treatments,exploring before and after freezing and thawing soil structure and nutrient cycling,bacteria,and change characteristics of soil such as multifunctionality,reveal the soil microenvironment for biochar and the response mechanism of freeze-thaw cycle.The main purpose of this study is to explore a suitable for in seasonal frozen crop habitat health regulation application mode and provide important guarantee for in seasonal frozen food production.The main conclusions are as follows:（1）Biochar improved the farmland soil structure in soybean and maize experimental areas,increased soil porosity and soil ventilation at the end of crop and the end of freeze-thaw period,and reduced soil compactness,and the effect was more obvious with the increase of biochar application amount;Biochar improved the soil solid and liquid phase ratio,reduced the soil gas phase ratio,adjusted the soil three-phase ratio,and increased the generalized soil structure coefficient,and B50was the best treatment.Biochar increased the aggregate content of 0.25-2 mm and>2 mm,and decreased the aggregate content of<0.053 mm and 0.053-0.25 mm,which improved the stability of soil aggregates and reduced the risk of soil degradation and soil erosion.B50 was the best treatment;By comparing the soil structure parameters under the two tillage methods,it was found that the soil porosity,ventilation,aggregate stability and generalized soil structure coefficient were larger and the soil compactness was smaller under the DT mode.The variance analysis showed that biochar,tillage and their interaction had significant effects on the input structure parameters.In addition,by comparing soil structure parameters at the end of crop and the end of freeze-thaw period,it was found that freeze-thaw cycle reduced soil structure,and biochar and DT could effectively alleviate the damage of freeze-thaw on soil structure.（2）Biochar and DT had certain effects on the spatial and temporal distribution of soil moisture and heat in soybean and maize test areas.In terms of spatial distribution,biochar and deep tillage did not change the spatial distribution characteristics of soil liquid water content and temperature,but increased the soil liquid water content and temperature of each layer,especially the soil surface,and B50 treatment was the best.In terms of time distribution,the liquid water content and temperature of surface soil（0-30 cm）were increased by biochar and DT,especially during spring sowing and freeze-thaw periods,that showed that biochar and DT could maintain the temperature and water required for crop emergence,which was beneficial to maintain soil temperature and soil water under freeze-thaw conditions.DT combined with 500 kg/mu biochar has the best effect on preserving soil moisture.In addition,biochar and DT improved the hydrothermal coupling between the growing period and the freeze-thaw period.The soil liquid water content showed a quadratic function relationship with temperature during the growing period and a threefold function relationship during the freeze-thaw period,and the relationship between B50 treatment under DT was the strongest.（3）Biochar and DT had certain effects on soil nutrients in soybean and maize test areas.The nutrient content decreased gradually with the deepening of soil layer,and the highest content was found in the surface layer.In terms of time,spring and summer are higher than autumn and winter,with the highest value in July-August and the lowest value in February.Biochar and DT increased the soil nutrient content,and the total organic carbon showed a gradual increase with the increase of biochar application amount,the largest increase in B100 treatment.The contents of ammonium nitrogen,nitrate nitrogen and available phosphorus in soil increased first and then decreased with the increase of biochar application.B50 was the best treatment.Deep tillage also increased the content of nutrient parameters,which was significantly different from that of ST.Redundancy analysis（RDA）showed that soil total organic carbon was positively correlated with porosity,and ammonium nitrogen,nitrate nitrogen and available phosphorus were positively correlated with soil GSSI,GMD and moisture.Therefore,we believe that soil TP is the key driving factor of TOC,and soil GSSI,GMD and liquid water content are the key factors affecting ammonium nitrogen,nitrate nitrogen and available phosphorus.（4）Biochar increased the richness and diversity of soil bacterial community and changed the relative abundance of soil bacteria.The specific performance is as follows:At the end of the period,the crop richness and diversity were the highest in B50 treatment and at the end of freeze-thaw period,the highest in B75 treatment,and biochar increased the relative abundance of soil Proteobacteria and Actinobacteriota.The relative abundance of Acidobacteria,Gemmatimonadota and Verrucomicrobia was decreased,and all of them were most decreased in B50 treatment.Comparing the community diversity in crop and freeze-thaw periods,it was found that the community diversity in crop period was higher than that in freeze-thaw periods,indicating that freeze-thaw cycles reduced the richness and diversity of soil bacteria.In addition,it can be seen from the number of soil bacteria before and after freezing-thawing that the number of unique bacteria before and after freezing-thawing decreases,indicating that the death number of soil bacteria in the freezing process is greater than the number of new bacteria in the thawing process,and the influence of soil bacteria in the freezing process is greater than that in the thawing process.（5）Biochar and freeze-thaw cycles have certain effects on soil bacteria distribution and network stability.Biochar enhanced the extension and postural characteristics（number of nodes,number of connections,average degree and modularity degree）of soil bacterial ecological network and improved the stability of symbiotic network.The topological characteristics of bacterial network of B25 and B50 treatments increased,while that of B75 treatments decreased.Biochar changed the distribution of soil bacteria before and after freezing-thawing,and biochar had a significant effect on the bacterial distribution of crops at the end of the period,and each treatment had a significant separation from CK,but had little effect on the end of the Freezing and thawing period.In addition,the freeze-thaw cycle reduces the stability of the soil bacterium ecological symbiosis network,compared with the crops in the final,freezing and thawing of the final reduced bacteria network topology characteristics,modules 4,5,and 6 are declined,showed that freezing and thawing effect does not change the main advantage of soil bacteria species,but by changing the potential to change the soil bacteria species in the ecological network.Stamp analysis showed that there were significant differences in 15 bacterial categories before and after freeze-thaw,indicating that the freeze-thaw cycle changed the bacterial community niche by affecting the 15 groups in symbiotic network module 4,module 5 and module 6.（6）The freezing-thawing cycle reduced soil multifunctionality,while biochar improved soil multifunctionality before and after freezing-thawing,and B50 treatment had the best effect.Soil ecological multifunctionality is influenced by both biological and abiotic factors.From the abiotic perspective,soil multifunctionality is positively correlated with bacterial richness,diversity,soil TC,MBC,MBN,soil basic respiration,nitrogen mineralization and enzyme activities related to nitrogen and phosphorus cycling.From the biological perspective,the Actinobacteriota group is the main driving factor of soil versatility change under freeze-thaw conditions.Therefore,from the perspective of bacteria,we believe that the change of biochar and freeze-thaw cycle in soil versatility is mainly due to the change of Actinobacteriota group.（7）Biochar and DT had certain effects on the growth of soybean and maize.The application of biochar significantly improved the canopy part,root part,photosynthetic parameters and vegetation index of soybean and maize during the whole growth period,among which,the improvement effect of soybean under B75 treatment was the best,and that of maize under B50 treatment was the best.By comparing the two tillage methods,it was found that the growth indexes of soybean and maize were better under deep tillage condition,and the ANOVA results showed that biochar,tillage and their interaction had significant differences on the growth of soybean and maize.In addition,both biochar and DT can improve the yield and composition of soybean and maize.The soybean yield and composition of 750 kg/mu biochar under DT mode are the largest,and the maize yield and composition of 500 kg/mu biochar under DT mode are the largest.（8）Choose GSSI,GMD,K,soil temperature,liquid water content,TOC,NH₄⁺-N,NO₃^--N,available phosphorus,plant height,total root length,net photosynthetic rate,photochemical vegetation index,yield and net output value 15 crop habitat index,establish their habitat health evaluation system,and the Topsis model was used to evaluate the habitat health of soybean and maize,and then the habitat health resilience index was calculated.The results showed that in soybean habitat health system,B75 treatment under DT mode had better evaluation effect,and in maize habitat health system,B50 treatment under DT mode had better improvement effect.Therefore,the best control mode for the habitat health of soybean in cold area was DT combined with 750 kg/mu of biochar,and the best control mode for the habitat health of maize in cold area was DT combined with 500 kg/mu of biochar.In conclusion,biochar and DT can promote soil and water environment and crop growth in seasonal frozen soil area,and the health regulation effect of different crop habitats is different.Under the premise of considering agricultural soil and water environment,crop yield and economic benefits,the best regulation mode for soybean improvement was DT with 750 kg/mu of biochar,and the best regulation mode for maize improvement was DT with 500 kg/mu of biochar.The results of this study provided practical basis for soil improvement and practical production in seasonal frozen soil areas,which was conducive to sustainable agricultural development in seasonal frozen soil areas.