Exploring N fertilizer reduction and organic material addition practices: An examination of their alleviating effect on the nematode food web in cropland

Excessive nitrogen (N) fertilization in croplands results in environmental problems, such as soil quality deterioration, water contamination, and biodiversity losses, which threaten the sustainable development of soil ecosystems. The soil nematode food web plays key roles in soil organic matter decomposition and nutrient cycling, and thus the sustainable development of cropland ecosystems. However, how the negative impact from the excessive N fertilization on the nematode food web is effectively alleviated remains uncertain. This study aimed to explore the effects of different N fertilization management practices (N fertilizer reduction or organic material addition) on alleviating the negative effects on the nematode food web in croplands. Four treatments/ management practices were examined: conventional fertilization (N control), N fertilizer reduction of 100% (N-0), N fertilizer reduction of 50% (N-1), and conventional fertilization with organic material addition (N+S). The results showed that the abundance of nematodes and microbial phospholipid fatty acids (PLFAs) both increased in the treatments of N-0, N-1, and N(+S)compared with N. Besides, N(+S)also increased the nematodes' biomass, diversity, and metabolic footprint, which correspondingly strengthened the nutrient turnover through the nematode food web. Overall, two management practices 1)N fertilizer reduction and 2) organic material addition, differ in the abiotic or biotic process in alleviating the negative effects of N fertilization on the nematode food web. The reducing N fertilization can directly alleviate the negative effect of fertilizer on soil acidification and then benefit for the growth of microorganisms and nematodes. The exogenous carbon input from organic material addition might promote carbon flowing and immobilization into nematode food web, and ultimately enhance the stability of soil food web.