Differences in N fate and net eco-economic value between common urea and humic acid urea: Combined experiments using 15N tracer and field lysimeter

Compared to the limited performance of other high-efficiency urea products, humic acid urea (HAU) increased the grain yield of winter wheat as well as of summer maize. However, the effect of adding different amounts of humic acid (HA) on the fate of urea and comprehensive economic and environmental evaluations remains unclear. Four treatments (no urea (CK), common urea (U), HAU0.5, and HAU5) were compared in a 2-year winter wheat–summer maize rotation system. Compared to U, the grain yield of HAU treatments increased by 4.48–11.25 %, regardless of crop type, planting year, or HA addition level; this was partly attributable to the increased storage of soil available N, as confirmed by a simultaneous ¹⁵N tracing microplot experiment in the first winter wheat season. HAU inhibited the loss of reactive N (NH₃ volatilization, N₂O emission, and NO₃^--N leaching loss). The C footprint based on the yield and areas calculations for HAUs was 7.01–13.48 % and 3.53–5.54 % lower than that of U, respectively. Annual environmental damage costs and annual net ecosystem economic benefits were decreased and increased by 14.89 %–19.11 % and 6.38 %–9.23 %, respectively. Few agronomic and environmental differences were found between HAU5 and HAU0.5, although the former locked more ¹⁵N nutrients in the topsoil. This combined experiment using ¹⁵N tracer and field lysimeters showed that more nutrients from HAU were absorbed by crops and converted into grains, reducing the environmental risk of greenhouse gas emissions due to the release of unused nutrients from common U into farmland.