Objective To evaluate the soil acidification characteristics of sugarcane fields in Guangxi under different fertilization treatments and to provide a theoretical basis for mitigating soil-acidification in this region.

Methods Based on a long-term field experiment initiated in 2008, four treatments were established: no-fertilizer control (CK), recommended fertilization (OPT), increased N application (OPTN, 50% higher nitrogen (N) application rate than OPT) and recommended fertilization combined with sugarcane leaf mulching and returning (OPTS). Soil pH, exchangeable acidity, acidification rate, exchangeable base cations, cation exchange capacity (CEC), soil acid-base buffering capacity (pHBC) and soil nutrients indicators were determined after 16 years under different fertilization treatments.

Results After 16 years long-term experiments, compared with the initial soil, soil pH under CK, OPT, OPTN, and OPTS treatments decreased by 0.04, 1.74, 2.00, and 1.72 units, respectively. The corresponding soil acidification rates were 0.16, 9.62, 10.41, and 9.81 kmol/(hm²·a), respectively. The soil pH buffering capacity (pH) of the CK treatment was 24.00 mmol/(kg·pH). compared with CK, the pH buffering capacity under the other fertilization treatments increased by 20.32%-26.77% , with the greatest increase observed in OPTS treatment. Compared with the OPT treatment, the OPTN treatment increased exchangeable acidity, exchangeable aluminum(Al³⁺), and exchangeable hydrogen(H⁺) by 19.31%, 15.25%, and 54.75% respectively. The total exchangeable base cations decreased by 14.03%, and base saturation decreased by 15.10%. Soil pH decreased by 0.04 units, and the acidification rate increased by 8.22% under OPTN relative to OPT. Compared with the OPT treatment, the OPTS treatment increased exchangeable acidity and exchangeable H⁺ content by 17.82% and 69.27%, respectively. The total exchangeable base cations increased by 13.45%, mainly due to a 26.22% increase in exchangeable calcium content. CEC increased by 12.67%. However, there were no significant differences in soil pH and acidification rate. Under increased N fertilization, soil total phosphorus, available phosphorus, and available potassium contents decreased by 6.99%, 11.06%, and 27.11%, respectively. Under sugarcane leaf mulching and returning, soil organic matter, total N, and available N contents increased by 9.96%, 12.32%, and 26.40%, respectively, while available phosphorus and available potassium contents decreased by 17.15% and 34.65%, respectively. In terms of 5-year average sugarcane yield, compared with the OPT treatment, the OPTN treatment resulted in a 6.23% reduction, while the OPTS treatment increased by 2.68%.

Conclusions Long-term excessive N fertilization increased exchangeable H⁺ and Al³⁺ contents while reducing total exchangeable base cations. The increased fertilizer N was not efficiently utilized by sugarcane, further accelerating soil acidification. In contrast, long-term sugarcane leaf mulching and returning effectively increased total exchangeable base cations, CEC, and organic matter content, and improved soil nutrient supply and acid-base regulation capacity. Therefore, rational chemical fertilizer application combined with sugarcane residue mulching and returning can serve as an important strategy for managing soil acidification in lateritic red soil sugarcane fields in Guangxi.