Spatio-Temporal Variation Characteristics and Driving Factors of Paddy Soil pH Changes in Jiangxi Province

Taking paddy fields in Jiangxi Province as an example, this study aimed to clarify the characteristics of acidity changes in paddy fields from 2010s (2007-2014) to 2023, to quantitatively analyze the drivers and relative contributions of soil acidification in Jiangxi Province, and to explore the reasons for the changes in the contribution rate of each driver over time, so as to provide the theoretical basis for the improvement of arable land acidification and the enhancement of crop yields in Jiangxi Province.

Based on the public data of China Statistical Yearbook, Jiangxi Provincial Statistical Yearbook, Jiangxi Provincial Ecological Environment Statistical Bulletin, Jiangxi Provincial Cultivated Land Quality Long-term Positioning and Monitoring Report from 2010s to 2023, and related literature, the characteristics of the change of pH in paddy fields from 2010s to 2023 were clarified, the amount of nitrogen cycling, crop harvesting, and H⁺ production from acid deposition were calculated, respectively, and the contribution rate of three driver factors to the change of soil acidity was quantified.

The pH of paddy fields increased from 5.20 to 5.37 from 2010s to 2023, with an increase of 0.17 units; the proportion of strongly acidic soil (pH＜4.5) decreased from 0.02% to 0.00; the proportion of paddy fields with acidic soil (pH 4.5-5.5) decreased from 84.4% to 70.7%; the proportion of weakly acidic soil (pH 5.5-6.5) increased from 14.9% to 26.7%; neutral and alkaline soil (pH＞6.5) increased from 0.7% to 2.6%; about 26.8% of the paddy fields were acidified (∆pH＜0), The area of paddy fields with pH changes ranging from -0.50 to 0.00 accounted for approximately 25.0%, while the area of paddy fields with pH changes less than -0.5 accounted for approximately 1.8%; and about 73.2% of the paddy fields had stable or increasing pH (∆pH≥0). Soil acidity changes in paddy fields in Jiangxi Province were mainly driven by anthropogenic activities, with an average contribution of 72.3% from nitrogen cycling processes, including ammonium nitrogen nitrification, nitrate nitrogen leaching, and plant uptake of ammonium nitrogen releasing H⁺; crop harvesting took away saline ions with an average contribution of 27.7%, and acid deposition had a weak effect (0.04% on average). H⁺ production from the nitrogen cycle showed an overall decreasing trend from 21.93 kmol·hm^-2·a^-1 to 13.93 kmol·hm^-2·a^-1; H⁺ production from salt-based ions floated less, fluctuating between 6.02 kmol·hm^-2·a^-1 to 7.60 kmol·hm^-2·a^-1; the amount of H⁺ produced by acid deposition decreased slowly, from 0.04 kmol·hm^-2·a^-1 to 0.00 kmol·hm^-2·a^-1. Reducing the amount of H⁺ produced by the nitrogen cycle process was a key factor in curbing soil acidification.

The area of paddy fields with pH increase between 2010s and 2023 accounted for 73.2%, indicating that the soil acidification problem in Jiangxi Province has been alleviated. Nitrogen cycle was the main factor of acidity change in paddy fields, and the reduction of nitrogen fertilizer dosage was the main reason for the decrease of H⁺ production from nitrogen cycle, so optimizing fertilizer application technology and increasing organic fertilizer could effectively curb the acidification process, and improve the quality of arable land and crop yield.