Objective The aims were to explore the effects of application rates of Si-Ca-Mg soil conditioner on the physicochemical properties of acidic latosols, as well as the growth and nutrient accumulation of maize seedlings, in order to clarify the optimal application rates of the soil conditioner for different acidic latosols.

Method A pot experiment was conducted to investigate the effects of Si-Ca-Mg soil conditioner applied at rates of 0, 0.75, 1.50, 2.25, and 3.00 g kg⁻¹ (calculated based on CaO content) on soil nutrient dynamics, as well as the growth and nutrient accumulation of maize seedlings. Three types of acidic latosols were selected as the research substrates, including strongly acidic granite-derived latosol (pH 4.43), acidic sand-shale-derived latosol (pH 4.96), and weakly acidic granite-derived latosol (pH 5.51).

Result After the application of soil conditioner, the shoot dry weight of maize in strongly acidic and acidic soils increased by 1.56 - 3.08 g plant⁻¹ and 0.75 - 1.21 g plant⁻¹, respectively, while the root dry weight increased by 0.36 - 0.62 g plant⁻¹ and 0.35 - 0.52 g plant⁻¹, respectively. The pH values of all three soil types increased significantly. Meanwhile, the contents of soil exchangeable acid and exchangeable aluminum decreased significantly, with the maximum reduction rates reaching 80% and 78% for strongly acidic soil, 84% and 84% for acidic soil, and 86% and 54% for weakly acidic soil, respectively. Simultaneously, the contents of soil exchangeable calcium and magnesium in the three soils increased significantly, with exchangeable calcium content increasing by 89% - 244%, 86% - 234% and 88% - 174%, respectively. The application of soil conditioner significantly increased the accumulation of nitrogen, phosphorus, potassium, calcium and magnesium in the shoots of maize planted in strongly acidic and acidic soils. In strongly acidic and acidic soils, the acid injury threshold values of maize were pH 5.16 and pH 5.70, respectively. The optimal application rates of soil conditioner (calculated based on CaO content) were 0.75 g kg⁻¹ and 0.81 g kg⁻¹, respectively.

Conclusion Soil pH and exchangeable calcium content increased gradually with the increasing application rate of soil conditioner, whereas soil exchangeable acid and exchangeable aluminum contents decreased progressively. Significant improvements in acidification amelioration were observed in all three tested soils, with the best efficacy achieved in strongly acidic soil and the poorest in weakly acidic soil. In strongly acidic soil, the application of soil conditioner increased the shoot and root dry weights of maize and enhanced the nutrient accumulation in maize shoots. Since most latosols in Hainan are derived from granite, the recommended application rate of soil conditioner is 6000 kg hm⁻² for the strongly acidic granite-derived latosol (pH 4.43) in the Sanya Breeding Base of Hainan.