Addition of organic amendments is a commonly used practice to offset potential loss of soil organic matter from agricultural soils. The aim of the present study was to examine how long-term addition of organic matter affects the abundance of different soil biota across trophic levels and the role that the quality of the organic amendments plays. Here we used a 17-year-old fertilization experiment to investigate soil biota responses to four different organic fertilizers, compared with two mineral nitrogen fertilizers and no fertilization, where the organic fertilizers had similar carbon content but varied in their carbon to nitrogen ratios. We collected soil samples and measured a wide range of organisms belonging to different functional groups and trophic levels of the soil food web. Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between soil biota. The organic fertilizers generally enhanced bacteria and earthworms. Fungi and nematodes responded positively to certain mineral and organic fertilizers, indicating that multiple factors influenced by the fertilization may affect these heterogeneous groups. Springtails and mites were less affected by fertilization than the other groups, as they were present at relatively high abundances even in the unfertilized treatment. However, soil pH had a great influence on springtail abundance. In summary, the specific fertilizer was more important in determining the numerical and compositional responses of soil biota than whether it was mineral or organic. Overall, biennial organic amendments emerge as insufficient, by themselves, to promote soil organisms in the long run, and would need to be added annually or combined with other practices affecting soil quality, such as no or reduced tillage and other crop rotations, to have a beneficial effect.

中文翻译：

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有机肥料类型而不是有机改良剂本身增加了土壤生物群的丰富度


添加有机改良剂是抵消农业土壤中土壤有机质潜在损失的常用做法。本研究的目的是研究长期添加有机物如何影响营养级不同土壤生物群的丰度以及有机改良剂质量所起的作用。在这里，我们使用了 17 年的施肥实验来研究土壤生物群对四种不同有机肥料的反应，并与两种矿物氮肥和不施肥进行比较，其中有机肥料具有相似的碳含量，但碳氮比不同。我们收集了土壤样本，并测量了属于土壤食物网不同功能组和营养级的各种生物体。与未施肥的土壤相比，长期添加有机和矿物肥料对大多数土壤生物的丰度产生有益影响，但土壤生物群之间的反应不同。有机肥料一般会增强细菌和蚯蚓的生长。真菌和线虫对某些矿物和有机肥料有积极的反应，表明受施肥影响的多种因素可能会影响这些异质类群。与其他群体相比，跳尾虫和螨虫受施肥的影响较小，因为即使在未受精的处理中，它们也以相对较高的丰度存在。然而，土壤pH值对跳虫丰度影响较大。总之，特定肥料在确定土壤生物群的数量和组成响应方面比矿物肥料或有机肥料更重要。 总体而言，从长远来看，两年一次的有机改良剂本身不足以促进土壤生物，需要每年添加或与影响土壤质量的其他做法相结合，例如免耕或减少耕作和其他作物轮作，起到有益的作用。