Stoichiometric analysis of an arable crop–soil–microbe system after repeated fertilizer and compost application for 10 years

Purpose: Little is known about the impact application of fertilizer and manure nutrients on the nutrient stoichiometry of crop–soil–microbe systems. We ask the question to what extent the nutrient availability in the microbe–soil–plant system may be affected by the application of fertilizers or manures. Methods: The influence of application of inorganic fertilizers or composted manure on the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and their stoichiometric ratios in soil, microbial biomass, enzymes, and plant tissues within the rhizosphere of maize was investigated in a maize–wheat rotation established for 10 years in China. Results: The higher rate of composted manure was most effective in increasing soil C, N, and P contents and the microbial biomass. Microbes changed biomass stoichiometry instead of regulating related enzyme secretion under different nutrient supplies. Although plants and microbes showed tight but different relationships with the two nutrient sources, competition for N consistently occurred. Pearson’s inter-correlation demonstrates stable Redfield-like C:N:P fractions existed in soil properties and related enzyme activity, but was not always found in crop and microbial biomass after fertilizer and manure application. Conclusions: The results indicate that soil microbial functioning and coupled feedback with the plants are important in maintaining the stability of fertilized/manured agricultural ecosystems.