Legume biological nitrogen fixation improves but chemical nitrogen fertilizer suppresses soil nematode communities in a Camellia oleifera plantation

Legume intercropping by biological nitrogen (N) fixation is supposed as a more sustainable way than chemical N addition to enhance soil N availability in agronomy, however, the effects of the two types of N input on soil food web are scarcely determined. To fill the knowledge gap, we conducted a field experiment with randomized block design in an oil‐tea (Camellia oleifera) plantation, which included five N manipulation treatment: legume intercropping (Arachis hypogaea and Cassia tora), chemical N fertilizer application (84 and 168 kg N ha−1 yr−1), and the control (no N addition). The soil nematode communities and physicochemical properties were monitored in the seedling, heading, and mature stages of the legumes respectively. The results showed that the legume intercropping significantly increased the abundances of bacterivores and omnivore‐predators compared with the N fertilizations. Weighted nematode fauna analysis showed that N fertilization treatments were mainly located in the degraded plot (quadrat IV), and legume treatments were located in the structure plot (quadrat III). Structural equation model revealed that the legume intercropping positively correlated with the abundance of bacterivores and omnivore‐predators while N fertilization rate negatively correlated with the abundance of bacterivores and fungivores. Our results suggest that the legume biological N fixation was more conducive to providing N sources to soil organisms than the chemical N fertilizer, which resulted in an enhanced and a degraded soil food web respectively. Thus, legume intercropping is a more sustainable N management practice for the cultivation of C. oleifera plantations.