Humic acid urea boosts cotton yield and fiber quality with net life-cycle carbon benefits despite higher production-stage burdens

To systematically evaluate the effects of applying humic acid urea (HAU) in cotton fields and its associated environmental impacts, this study used the ReCiPe method to assess the environmental burden of HAU at the production stage, conducted field experiments to investigate its effects on cotton yield, quality, economic benefits, and greenhouse gas (GHG) emissions, and calculated the full life‑cycle carbon footprint of HAU. The results indicated that, per ton of nitrogen (N) produced, the midpoint environmental impact categories of HAU were similar to those of conventional urea (CU), primarily associated with freshwater ecotoxicity, marine ecotoxicity, human carcinogenic toxicity, and non-carcinogenic toxicity, with coal, natural gas, and electricity consumption being the dominant contributors. The overall environmental burden of HAU was only 1.84% higher than that of CU. In field trials, compared with CU, HAU significantly increased seed cotton yield (5.67%) and lint yield (4.53%), and improved fiber length, fiber strength, elongation, and micronaire by 3.05%, 3.31%, 2.60%, and 6.02%, respectively ( P < 0.05), resulting in a conservative estimate of 10.91% increase in economic returns under equal pricing ( P < 0.05). HAU also reduced field-level GHG emissions by 9.25% ( P < 0.05). When accounting for emissions from production, transport, and application per ton of N, the full life-cycle carbon footprint of HAU was 5.94% lower than that of CU ( P < 0.05). Overall, these results support the use of HAU as a sustainable N management tool for Xinjiang’s cotton production, contributing to both economic returns and carbon footprint reduction.