Responses Of Soil Nematode Assemblages To Long-Term Application Of Inorganic Fertilizers And Organic Materials In Upland Red Soil

Red soil degradation is a consequence of long-term combined impacts of irrational land use and natural conditions in south of China. To improve the soil quality of the degraded red soil, the key point is the restoration and reconstruction of soil nutrient pool. Rational fertilization managements are considered as an important aspect of soil nutrient restoration and ecological functions of arable soil. Soil nematode assemblage is well-known as a good indicator to the status of soil ecosystem in farm ecosystem. Based on the long-term experiments in an upland field, the impacts of long-term application of inorganic fertilization and organic materials on seasonal distribution, community structure of soil nematodes were studied. We also analyzed the relationship between nematode assemblage and soil quality indexes to explore the response of nematode assemblages to different fertilizations and the indication to soil fertility. The main results are as follows:1. Significant differences among treatments were observed for total nematode abundance, trophic groups and ecological indices (p< 0.05) in inorganic fertilizer experiments. The total nematode abundance decreased in the following order PK (phosphorus and potassium fertilizers)> NPKCaS (NPK plus gypsum fertilizers)> NPK (nitrogen, phosphorus and potassium fertilizers)> NP (nitrogen and phosphorus fertilizers)> NK (nitrogen and potassium fertilizers). The total number of nematodes was significantly higher in NPKCaS and PK than in NPK, NP and NK except in May. Plant parasitic nematodes were the dominant trophic group in all treatments excepted in NPKCaS, with their proportion ranged between 38% and 65%. The dominant trophic group in NPKCaS was bacterivores with the proportion being 42.1%. Redundancy analysis (RDA) revealed that pH has the greatest effect on soil nematode functional guilds. Furthermore, the higher value of maturity index, Wasilewska index and Structure index in NPKCaS indicated that the combined application of NPK and gypsum could remarkably relieve soil acidification, resulting in a more mature and stable soil food web. While, that of the NK was in adverse.2. The results of long-term different organic material experiments indicated that the nematode assemblage fluctuated among different treatments during the peanut growth season. Organic amendments stimulated the total nematode abundance, the proportion of bacterial and fungal-feeding nematode and predators/omnivores, but suppressed the plant parasitic nematodes. The total nematode abundance decreased in the following order as CK+PM (NPK plus pig manure)> CK+GM (NPK plus green manure)> CK+St (NPK plus straw)> CK (NPK)> CK+Re (NPK plus return). The numbers of bacterivore and fungivore belonging to cp-1,2 guilds (Bal, Ba2 and Fu2) were higher in the CK+Re, indicating of a high resource availability status. The highest average proportion of predators/omnivores in pig manure treatment resulted in corresponding highest SI among all treatments, suggesting a complex community structure. Notably, organic amendments could increase soil organic matter content. Except the treatment with green manure, pH in other organic treatments was significantly improved than the control, manure increased the contents soil alkaline N and available P, while the the crop residues increased soil available K content significantly. Together, the manure is more conductive to improve red soil, and the effects of the other three crop residues on degraded soil depended on the straw types and the types of fertilization.In conclusion, our study demonstrated that the application of both gypsum and phosphate is an effective practice to improve red soil quality. Differences among various organic amendments showed different effects on soil nematode communities, highlighting the potential benefits of combining different organic amendments in improving red soil fertility. Overall, the analysis of nematode assemblage is relevant to the impact of different fertilizers on the red soil quality, promoting a comprehensive understanding the structures and functions of soil ecosystem affected by different fertilization managements, and providing a guide for the rational and effective application of chemical and organic fertilizations in red soil region.