Long-term returning agricultural residues increases soil microbe-nematode network complexity and ecosystem multifunctionality

Abstract

The negative environmental impacts of chemical fertilizers have been recognized for a long time, and the returning of agricultural residues to the soil is considered a sustainable agricultural practice. However, few studies have focused on the ecological and economic benefits of returning agricultural residues to the soil simultaneously. Using a 16-year field experiment, we integrally evaluated and compared the ecological and economic benefits of six fertilization practices. The treatments included a no-fertilizer control, conventional chemical NPK fertilization, and partial substitutions of the NPK in chemical fertilizers with a low (30%) or high (60%) level of agricultural residues (straw or cattle manure). The amount of N, P and K inputs remained constant across all fertilization treatments, but the source of N, P and K differed. Ecological benefits were assessed through a study of ecosystem multifunctionality and through a co-occurrence network analysis of the soil micro-food web. Our results showed that applications of agricultural residues increased soil microbial biomass and diversity, soil co-occurrence network complexity, and ecosystem multifunctionality compared with the chemical fertilization alone. The high-level straw substitution treatment supported the greatest ecosystem multifunctionality and soil network complexity. Random Forest regression analysis revealed that soil microbial biomass and fungal diversity were important biological traits associated with ecosystem multifunctionality. The economic benefit was highest when cattle manure was returned to the soil, lowest when crop straw was returned to the soil, and intermediate with chemical fertilization alone. Therefore, the return of cattle manure to the soil provided comprehensive ecosystem services. Our findings increase the understanding of the relationships between economic and ecological effects of returning agricultural residues to the soil.