| Extensive use of chemical fertilizers has caused serious environmental problems and restricted agricultural sustainable development. Organic fertilizer application can improve soil structure and fertility and straw incorporation can also improve soil nutrient content. Soil nematodes are sensitive indicators of soil environmental changes, which have potential to evaluate soil environment conditions of different agricultural management practices and guide farmland rational fertilization. North China Plain, one of China’s major grain producing and highest usage of chemical fertilizers regions, is essential to maintain agricultural sustainable development in this region. At present, few researches have involved the responses of soil nematode assemblage dynamics to fertilization managements under both wheat and maize rotation system in this area. The research site is located in Quzhou experiment station of China agricultural university. The field experiment designed to have six treatments including CK (no fertilizer); CF (chemical fertilizer); PF (composted pig manure and chemical fertilizer); SF (straw and chemical fertilizer); PSF (composted pig manure and straw and chemical fertilizer); PMF (composted pig manure based organic-inorganic complex fertilizer and chemical fertilizer) were conducted to expore the effects of different fertilization managements on nematode assemblages at maize and wheat harvesting stages and find out fertilization measures which could improve soil quality by nematode ecological indices. Simultaneously, the relationship between soil nematode assemblages and soil environmental factors was investigated. The results are as follows:1) Combined application of organic manure, straw and chemical fertilizer promoted the contents of soil organic carbon and total nitrogen, even some fertilization combinations reached significant differences in comparison with CK and CF(P<0.05). Combination of organic and inorganic fertilizer also increased the contents of soil microbial biomass carbon and basal respiration, significant differences were found in the part of the sampling times (P< 0.05). Metabolic profiles of soil microbial communities were measured by MicroRespTM, principal component analysis (PCA) showed the situation of carbon source utilization by microbes in different fertilization treatments changed apparently.2) A total of 31 genera of soil nematodes were found at maize harvesting stage, including 13 genera of bacterivores,6 genera of fungivores,4 genera of herbivores and 8 genera of omnivores/carnivores; 27 genera of soil nematodes were found at wheat harvesting stage, including 11 genera of bacterivores,5 genera of fungivores,4 genera of herbivores and 7 genera of omnivores/carnivores. Diploscapter, Plectus, Leptonchus and Pungentus were only found at maize harvesting stage, Acrobeloides and Helicotylenchus were dominant genera at both stages.3) Compared with CK, all the fertilization practices enhanced the number of soil nematodes, especially SF and PSF treatments increased the number of soil nematodes significantly (P< 0.05). The trend of bacterivores was similar to the total nematodes. At maize harvesting stage, no significant difference was found in the number of fungivores basically, while the number of fungivores in SF was significantly higher than CF at wheat harvesting stage (P< 0.05). In addition to the number of herbivores in PMF was significantly higher than other five treatment (P< 0.05) at maize harvesting stage of 2011 and wheat harvesting stage of 2012, no significant difference in the number of herbivores of each treatment was found at the rest of the sampling period. Omnivores/carnivores at each treatment had no significant difference at maize harvesting stage, while organic-inorganic fertilization treatments at wheat harvesting stage increased the number of omnivores/carnivores apparently.4) Non-metric multidimensional scaling analysis showed that nematode assemblages under different sampling times were clearly separated from each other, while not under different fertilization treatments. Cluster analysis at 50% similarity level indicated nematode assemblages in PF, SF and PSF treatments differ with CK and CF treatments apparently. Further analysis by ANOSIM, no significant difference of nematode assemblages was found between any two treatments at maize harvesting stage, while significant differences of nematode assemblages at wheat harvesting stage was found in comparison CK with PSF and PMF, PMF with PF, SF and PSF (P< 0.05). The analysis of structural equation model showed that organic manure and straw application increased soil organic carbon and microbial biomass carbon concentration and then increased the abundance of bacterivores, fungivores and omnivores/carnivores, but nitrate nitrogen had inhibitory effect on the three kinds of nematodes.5) This study found that enrichment index (E1) and structure index (SI) had an increasing trend in organic-inorganic fertilizer treatments and it indicated that soil resources situation was getting better and the degree of disturbance reduced. Meanwhile, soil nutrient status was gradual improvement with the increasing of fertilization duration. Channel index (CI) showed soil food web shift from fungal decomposition pathways to bacterial decomposition pathways by organic-inorganic fertilization application. The values of soil Biological quality index (Fc) in organic-inorganic fertilization treatments were higher than in chemical fertilizer and control treatments, it indicated organic-inorganic fertilization improved soil quality.In summary, soil nematodes showed different responses to fertilization practices and sampling times and had certain potential indicative values to the change of farmland ecosystem under different fertilization managements. The results of this experiment showed that SF and PSF fertilization managements were benefit for improving soil quality and it had a certain reference value to guide rational fertilization of North China Plain agricultural area. |
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