Effects Of Chemical Fertilizer Reduction With Supplementing Different Organic Amendments On Nematode Community In Upland Red Soil

Based on reducing the input of chemical fertilizer and importing organic materials,ecological intensive agriculture has been proved to be effective in promoting the development of soil biological community and increasing soil ecosystem multifunction.Plenty of studies from natural ecosystem show that the quality of organic materials influence the process of energy flow,nutrient transformation and carbon sequestration in soil during the decomposition process,which are the key to support the structure and function of soil food web.Exploring the changes of the soil community and function conducted by organic materials quality is considered as the effective approach to reveal the regulation mechanism of terrestrial ecosystem functions,which is also an important basement for rational use and management of organic material resources.Soil nematodes,one of the most abundant groups and different trophic levels,are occupying central positions in the soil food web and also responing quickly to the changes of soil condition.So they has unique advantages in reflecting the changes of soil food web structure and function under the influence of resource quality.Red soil is the main type of soils in the tropical and subtropical regions of southern China,which is rich in hydrothermal conditions,while fragile in soil ecosystem.It is urgent to restore the red soil biological community and function in order to maintain the sustainable development of agriculture.In this research,soil nematodes communities under different organic amendment were investigated in order to better understanding the effects of organic materials on soil community and agricultural ecosystem function,furthermore,to provide a theoretical basis of ecological intensive agriculture.The field experiments were established in 2015,which were conducted to study the effects of different quality straw-derived and dung-derived organic materials on soil nematodes community and structure.There were two sections in this research where the chemical fertilizer and chemical fertilizer reduction treatments were used in common and organic materials were separated by different derivation.Six treatments in four replicates plot were investigated in experiment I:(1)NPK(chemical fertilizer);(2)60%NPK(chemical fertilizer reduction);(3)NPK+straw(chemical fertilizer combined with straw);(4)60%NPK+straw(chemical fertilizer reduction combined with straw);(5)NPK+biochar(chemical fertilizer combined with biochar);(6)60%NPK+biochar(chemical fertilizer reduction combined with biochar).Four treatments in four replicates plot were investigated in second experiment:the first two treatments were used in common with the first experiment;(3)60%NPK+conventional compost(chemical fertilizer reduction combined with conventional compost);(4)60%NPK+vermicompost(chemical fertilizer reduction combined with vermicompost);Based on the investment of nematodes community in sweet potato(Ipomoea batatas L)and oilseed rape(Brassica napus L)phase under different organic amendments for two years,this research discussed the effect of organic material quality on soil nematodes community and structure,furthermore,the response mechanism of nematodes community was also studied incorporated with soil physiochemical properties.The main results of first experiment showed that:(1)Compared to chemical fertilizer treatment,chemical fertilizer reduction significantly increased nematode margalef index,enrichment index,and also increased the complexity and connection of nematodes community network.While there were no significant differences between nematodes abundance and abundance of different trophic group.(2)Chemical fertilizer combined straw and biochar had no significant effect on nematode abundance,while chemical fertilizer reduction combined straw and biochar significantly increased nematode abundance,and recalcitrant biochar(low quality)showed higher improvement on nematode abundance.(3)Whether chemical fertilizer reduced or not,straw and biochar amendment could increase the omnivores-predators abundance,nematode margalef index,maturity index,structure index,and metabolic footprint.(4)The labile straw(high-quality)decreased the relative abundance of herbivores,while increased the abundance of bacterivores and the complexity of soil nematode community network,which reflected the higher turnover rate of organic matter,nutrient cycling rate,and soil microbial activity.On the other hand,recalcitrant biochar(low-quality)showed lower enhancement of maturity index,but increased fungivores significantly,which indicated the decomposition progresses shifting from bacteria to fungi,as well as decreased the nitrogen mineralization rate and the complexity of nematode community network.The main results of the second experiment showed that:(1)Conventional compost and vermicompost significantly increased soil nematode abundance,while vermicompost containing more active resources showed lower improvement on nematode abundance.(2)Conventional compost and vermicompost significantly increased the bacterivores and fungivores abundance,enrichment index and structure index,and promoted the complexity of soil nematode community network.(3)Compared to conventional compost,vermicompost decreased herbivores abundance,while increased omnivores-predators,margalef index,shannon-wiener's diversity index,maturity index and metabolic footprint,resulting in improving the complexity of nematode community network.In summary,whether it is straw-derived and dung-derived,organic materials with low C/N,simple organic carbon structure or more active resources can maintain more complex nematode community structure,while organic materials with high C/N,complex organic carbon structure or less active resoures can support more soil nematode abundance.