Quantifying the effect of diammonium phosphate replacing fused calcium magnesium phosphate on soil acidification rate in sugarcane fields based on conservative ion cycling

Abstract

Abstract Background and aim In recent years, diammonium phosphate (DAP) has gradually replaced fused calcium magnesium phosphate (FCMP) as the main source of phosphorus in sugarcane fields in China. This substitution tended to accelerate soil acidification. We aim to quantify the effect of DAP replacing FCMP on soil acidification rate (SAR) by using conservative ion cycling. Methods A 3-yr experiment in a sugarcane field was performed. We use conservative ions to assessed conservative alkalinity (CA), and CA was defined by subtracting the sum of the charges of conservative anions (SO42− and Cl−) from the sum of the charges of conservative cations (K+, Na+, Ca2+, and Mg2+). SAR was assessed by the input and output of CA. Results CA loss and H+ production have a significant positive correlation. In sugarcane field, CA was output from topsoil by 7.1 to 8.9 kmolc ha–1 yr–1 through leaching and sugarcane harvesting, which continuously acidified the topsoil. Among them, sugarcane removal and leaching contributed 62–66% and 34–38%, respectively. The CA input by deposition alleviated 7.7–9.7% of the CA output. When the FCMP application rate was 500 kg ha–1 yr–1 on average, fertilization alleviated 105.8% of the CA output. When FCMP was replaced by DAP, the SAR increased by 7.4 kmolc ha–1 yr–1. Conclusions Replacing FCMP with DAP changes conservative ion cycling, causes the soil to lose more CA, and increases the SAR in sugarcane fields in China. Its subsequent impact on sugarcane production requires further attention.