Parent material and altitude influence red soil acidification after converted rice paddy to upland in a hilly region of southern China

Purpose Land use conversion from rice paddy to upland has been shown to decrease soil pH due to enhanced proton production from nitrification of ammonium-based N fertilizers and base cation loss. Parent material and altitude have a dominant impact on spatiotemporal distribution of soil base cations, but little information is available about their effects on soil acidification. This study examined changes in acidity indicators after the conversion, and their relationship with parent materials and altitude in a typical hilly region of southern China. Materials and methods To explore the effects, soils derived from limestone, quaternary red clay, and sandshale were sampled from 11 sites in Qiyang and Qidong counties, Hunan Province, China. In each sampling site, paddy field as control and upland maize under different conversion ages were selected in adjacent and pairs. The information on management and conversion ages were surveyed from local farmers, and altitude was recorded for each site. Soil pH, exchangeable acidity, base cations, cation exchange capacity, soil organic matter, nutrients, and their inner relationships were examined. Results and discussion The conversion significantly decreased soil pH, which was parent material dependent. Soils derived from limestone had much higher pH than that from quaternary red clay and sandshale. Soil pH negatively correlated with altitude ranging from 96.2 to 138.3 m in the study area. The conversion significantly increased exchangeable acidity of soils derived from quaternary red clay and sandshale by 1.53 and 1.13 cmol (+) kg −1 , respectively, dominated by Al, but no change for soils derived from limestone. The boosted regression tree model driven by soil properties explained 96.5%, 91.8%, and 98.1% of the pH variation of soils derived from limestone, quaternary red clay, and sandshale, respectively. Soil exchangeable Ca was the most influential trigger on pH variability of limestone- and quaternary red clay-derived soils, while soil total N and available N loss played critical roles in accelerating acidification of sandshale-derived soils after land use conversion. Conclusions Our data indicated that Ca and N loss play critical roles in accelerating soil acidification from enhanced nitrification after land use conversion in the red soil hilly region, which could be influenced by parent materials and altitude. Practices such as liming, straw mulching, or catch crop should be taken to prevent Ca and N loss, and alleviate acidification as the conversion occurring, especially for soils at high altitude.