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This paper investigates the effects of different long-term (36 years) fertilizer treatments on soil pH, exchangeable acids, exchangeable base cation and cation exchange capacity (CEC) at 0–10 cm and 10–20 cm soil layers in a double-cropping rice field. The following fertilizer treatments were included: chemical fertilizer (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without any fertilizer input as a control (CK). This result indicated that soil pH at 0–10 cm layer with RF and OM treatments was higher than that of MF and CK treatments. Soil exchangeable acidity content at 0–10 cm and 10–20 cm layers with RF and OM treatments were decreased by 48.4%, 51.6% and 49.2%, 54.2%, compared with CK treatment, respectively. Soil exchangeable calcium (Ca2+), magnesium (Mg2+) and potassium (K+) contents at 0–10 cm and 10–20 cm layers in paddy field with OM and RF treatments were higher than that of CK treatment. Moreover, compared with CK treatment, soil exchangeable base ion content at 0–10 cm and 10–20 cm layers in paddy field with OM treatment were increased by 54.1% and 42.6%, respectively. Soil CEC and effective cation exchange capacity (ECEC) at 0–10 cm and 10–20 cm layers with OM and RF treatments were significantly higher than that of MF and CK treatments. In conclusion, our results indicated that long-term application of crop residue or organic manure can improve soil exchangeable base ion and exchangeable capacity contents, alleviate soil acidity in a double-cropping paddy field. [ABSTRACT FROM AUTHOR]

While the application of manure to improve soil quality has attracted attention, the effect of pig manure application rates on soil acidity remains poorly understood. In this study, we analyzed the changes and correlations between soil acidity, pH buffer capacity (pHBC), soil chemical properties, and crop yields after 8 years of pig manure application at different rates (i.e., 0, 7.5, 15, 30, and 45 Mg ha−1) in a red upland soil (Ultisol). With an increase in the application rates, the crop yields were 0.77–8.85 times higher; the pH was enhanced by 0.4–0.8 units; and the soil organic matter (SOM), pHBC, iron activation (Feo), exchangeable calcium (ExCa), and exchangeable magnesium (ExMg) contents increased by up to 74.1%, 92.7%, 36.7%, 62.2%, and 48.7%, respectively, whereas that of total exchangeable acid (ExAcid) decreased by 17.2–52.9%. The crop yields were positively related to the soil pH but negatively correlated with ExAcid. Redundancy analysis revealed ExAcid and pHBC were more sensitive than pH was to the other chemical indicators. ExAcid was negatively correlated with SOM and ExCa; pHBC was positively correlated with ExMg, TN, SOM, and Feo. In conclusion, the crop yield could be improved by adjusting the soil acidity characteristics, and the application of pig manure reduced the soil acidity, with an optimal application rate of 15 Mg·ha−1. [ABSTRACT FROM AUTHOR]