Lime requirement determination for acidic soils based on the measurement of soil mobilized aluminum with a portable colorimeter under field conditions.

Currently, the lime requirement calculation models for ameliorating acidic soils required laboratory analyses of soil samples to obtain necessary parameters. This study established a rapid method for determining soil mobilized aluminum (Al) content under field conditions. Then, based on the soil mobilized Al content, the lime requirement to ameliorate acidic soils was calculated. Incubation experiments were conducted to examine the feasibility and reliability of the new method. Finally, the field experiment was conducted to confirm the feasibility and reliability of the method under field conditions. Method validation revealed the chromium azurol S-colorimetric approach for soil mobilized Al with a portable colorimeter was satisfied for two critical analytical criteria: (1) measurement accuracy comparable to reference methods (95.8-104.1 % recovery) and (2) operational simplicity suitable for field deployment. According to soil pH and mobilized Al, the [OH]/[Al] molar ratio of mobilized Al and the amount of alkali required to completely transform the mobilized Al into Al(OH)3 were calculated, and thus lime requirement was estimated. This method could quickly determine the lime requirement for ameliorating acidic soil under field conditions, and soil mobilized Al content significantly decreased from 12.71 mmol kg-1 to 1.63 mmol kg-1 and the rapeseed yield increased by 38 % with the lime dosage estimated using the method. Therefore, quick and accurate determination of lime requirement for acidic soils can be achieved based on the measurement of soil mobilized Al, which enhanced the efficiency of soil acidity diagnosis and decision-making for ameliorating acidic soils.