Responses Of Soil Nematode Communities To Biochar And Nematode Inhibitors Combined With Fertilizer And Their Ecological Indicators In Dryland Wheat Fields

Soil nematode communities have important ecological functions and are good indicators of farmland ecosystem health.Long-term application of chemical fertilizers not only had negative effects on soil physical and chemical properties,but also caused the outbreak of herbivorous nematodes,resulting in crop yield reduction.The combined application of biochar and chemical fertilizer can improve soil physical and chemical properties and regulate the structure and function of soil nematode community,while the application of nematode inhibitor can directly inhibit the damage of herbivorous nematodes to crops,but also affect the ecological function of nematode community.Therefore,biochar,fertilizer and nematode inhibitors may have a complex combined effect on soil nematode community in farmland.The loess Plateau is a traditional dry farming region in China.The unreasonable application of chemical fertilizer is widespread in this region,and the control of herbivorous nematodes has not been paid enough attention in this region.This study of the loess tableland area of dry land wheat field as the research object,using field plot test,the biological carbon,fertilizer and nematodes inhibitors on the influence of soil nematode community,nematode community and soil physical and chemical properties were analyzed and the relationship between the growth and yield of wheat,has been clear about the nematode community in biochar,fertilizer and the role of the nematode inhibitors of farmland ecological effect.The main results of this study are as follows:（1）Application of biochar,chemical fertilizer and nematode inhibitor can significantly affect the growth,nutrient accumulation and yield of wheat,and change the physical and chemical properties of soil.Compared with single application of chemical fertilizer,biochar combined with chemical fertilizer increased dry matter quality,effective panicle number and yield by 78.57%,28.83%and 52.90%,respectively.Nematode inhibitor promoted the root growth of wheat at late growth stage.The combined application of biochar,chemical fertilizer and nematode inhibitor could improve the dry matter quality of wheat root system,promote the accumulation of nitrogen and phosphorus and the proportion of nitrogen and phosphorus in wheat head,and significantly increase the 1000-grain weight of wheat（49.15g）.Compared with the single application of chemical fertilizer,the combined application of biochar and chemical fertilizer effectively alleviated the decrease of soil organic carbon content at the end of wheat growth,promoted the slow release of nutrients,and reduced the content of soil available P and ammonium nitrate nitrogen by 42.26%and82.84%at jointing stage,but increased significantly at heading stage and maturity stage.Combined application of biochar,chemical fertilizer and nematode inhibitor significantly increased soil total nitrogen(1.08±0.03g·kg^-1)and organic carbon content(13.5g·kg^-1)at mature stage.（2）Application of biochar,chemical fertilizer and nematode inhibitor changed soil nematode community structure,ecological function index and network characteristics.The average individual density of nematodes was 1124 per 100 g^-1in dry soil,which belonged to 64 genera,33 families,7 orders,2 classes,including 19genera of bacterial-feeding nematodes,12 genera of fungivores nematodes,11 genera of herbivorous nematodes and 22 genera of omnivorous/predatory nematodes.Fertilizer application reduced the number of nematodes,Shannon diversity index H’,enrichment index EI and structure index SI,and increased the plant parasitic nematodes index PPI.The combined application of biochar and chemical fertilizer effectively alleviated the decrease of nematode diversity caused by fertilization,and increased the relative abundance of microbivorous nematodes and omnivorous/predatory nematodes,and promoted the structural degree and stability of soil food web.However,the relative abundance of phytophagous nematodes also increased to 77.14%with crop growth.Nematode inhibitors significantly reduced the number of nematodes（by 52.78%-107.49%）,but promoted the increase of shannon diversity index（H’）at heading and maturity stage,and enhanced the negative correlation between the herbivorous nematodes and the omnivorous/predatory nematodes.Therefore,the combination of fertilizer and biochar（YNPB）increased the maturity index MI and structure index SI,but also decreased the abundance of herbivorous nematodes by 90.92%,alleviated the harm of herbivorous nematodes,and promoted the growth of wheat roots.（3）Soil nematode community characteristics can effectively indicate the ecological effects of biochar,fertilizer and nematode inhibitors on farmland.Soil moisture content,p H,organic carbon,ammonium nitrate nitrogen and microbial biomass carbon and nitrogen had significant effects on soil nematode community composition,ecological index and network characteristics.Soil nematode index（NCI）and plant parasitic nematode index（PPI）were directly or indirectly regulated by different anthropogenic management measures,which affected the growth and yield of wheat mainly through affecting soil available nutrients and organic carbon content.Compared with chemical fertilizer,nematode inhibitors and biochar significantly reduced the number of herbivorous nematodes and plant parasitic nematode index（PPI）,reduced the damage of herbivorous nematodes to wheat roots,promoted the increase of soil microbial biomass,and then increased the relative abundance of microbivorous nematodes and omnivorous/predatory nematodes.The nematode community diversity,maturity and stability were improved,and the nematode community comprehensive index（NCI）was increased,which promoted the growth and yield of wheat.The multi-function of farmland ecosystem（crop yield and soil physical and chemical properties）was the highest in YNPB treatment,and there was a significant quadratic correlation between the comprehensive index of nematode and the multi-function index of farmland ecosystem（P<0.05）.To sum up,biochar,fertilizer and nematodes inhibitors and their interactions by influencing the soil physical and chemical properties,effectively control the nematode community,and its effect on wheat growth and yield of nematode community characteristics and soil physical and chemical properties and closely related to wheat growth and yield,and nematodes composite index can effectively instructs the versatility of farmland ecosystem,The results provide a basis for evaluating the combined effects of biochar,fertilizer and nematode inhibitor on farmland ecosystem.