Humic Acids Incorporated into Urea at Different Proportions Increased Winter Wheat Yield and Optimized Fertilizer-Nitrogen Fate

Abstract

Humic acids (HAs) incorporated into urea fertilizers are highly effective at increasing yield and decreasing fertilizer-derived nitrogen (N) loss from soil, but reports of the optimal proportion in fertilizers remain widely inconsistent. In this study, we examined the effects of urea enhanced with 0.2–5.0% HAs (UHAs) on the yield, biomass production, N uptake, and N residue in fluvo-aquic soil in winter wheat cultivated over two growing seasons from 2018 to 2020 in the North China Plain. UHAs application significantly enhanced wheat grain yield, aboveground dry bio-mass, total and fertilizer-derived N uptake by wheat, and residue in soil, while reducing the loss of fertilizer-derived N. Additionally, UHAs treatments increased fertilizer-N residues in soil, especially in the top 30 cm soil layer, which increased with the proportion of added HAs. These positive effects were attributed to a higher spike number under UHAs treatments compared to conventional urea. Clustering analysis of the different treatments showed that 0.2% HAs were more similar to conventional urea, while 0.5% had similar effects to HAs at higher proportions. UHAs application significantly enhanced wheat grain yield, mainly via increasing spike number, and optimized the fertilizer-N fate. Among UHAs treatments, 0.5% HAs showed the highest increase in economic ben-efit.