Effect of different water and fertilizer coupling on soil nematode community structure and diversity in banana plantation

Abstract: Soil nematodes are the most abundant group of soil animals that rapidly react to environmental changes. In the farmland ecosystem, fertilizer and irrigation are two important factors influence the composition and diversity of soil nematode community. The effect of various water and fertilizer usages under a fertigation regime on the soil nematode community structure was investigated in a banana plantation of Hainan Province in this study. Four treatments were designed: A (low amount of water and fertilizer), B (low amount of fertilizer and high amount of water), C (high amount of fertilizer and low amount of water), and D (high amount of water and fertilizer). Soil samples were extracted using a soil corer (3.0 cm diameter) at a depth of 0-30 cm below the soil surface from July 2011 to June 2012 within the plant rows of banana plants, 50 cm from the base of the banana plant. The nematodes were extracted through the shallow basin method, and were identified to the genus level with the aid of a microscope. Results showed that significant treatment effects (P<0.01) were observed in the abundance of total nematodes, bacterivores, fungivores, plant parasites, omnivore-predators, the values of diversity (H￠), maturity index (MI), channel ratio (NCR), the wasilewska index (WI), and the enrichment index (EI) during the four sampling stages. Thirty-four nematode genera belonging to twenty-two families were identified during the sampling stages, of which Basiria and Paratylenchus were the dominant genera. The abundance of plant parasites and omnivore-predators in the C treatment and the abundance of total nematodes, bacterivores, and fungivores in the D treatment were significantly higher than in the other treatments. The values of MI and WI in the A treatment, the values of structure index (SI) and EI in the B treatment, the values of H￠ and NCR in the C treatment, and the values of thheplant parasite index (PPI) in the D treatment were significantly higher than in the other treatments. Significant sampling time effects (P < 0.01) were observed in the abundance of total nematodes, bacterivores, fungivores, plant parasites, the values of H￠, dominance (λ), PPI, NCR, WI, SI, and EI. The abundance of bacterivores, fungivores, and plant parasites at the booting and ripening stages were significantly higher than at the other stages. The values of H￠, NCR, SI, and EI at the seedling stage, the values of MI and WI at the jointing stage, the values of λ at the booting stage, and the values of PPI at the ripening stage were significantly higher than at the other stages. The analysis of NCR showed that bacterial decomposition was the major decomposition pathway in the soil organic substance decomposition system. The data from MI, PPI, SI, and EI demonstrated that the nematode community structure was more stable in the A and B treatments than in the C and D treatments. The excessive application of water and fertilizer increased the level of disturbance of the soil ecosystem and posed a significant threat to the soil environment. Nematodes could be used as bio-indicators for assessing soil quality under irrigation and fertilization.