Objectives Straw decayed products have been found of improving soil acidity and resisting soil acidification. This study compared the effects of two straw decayed products, to provide technological base for choosing efficient straws to inhibit the re-acidification of red soil.

Methods The lateritic red soil (pH 4.75) and latosol soil (pH 5.02), derived from granite and basalt respectively, were used as test soils, 2% of rice and pea straw decayed products (RSD, PSD) was added into the two soils to make four treatment soils. The control soils were prepared by adding Ca(OH)₂ to the same pH as the RSD and PSD treatments (RCK, PCK). All the eight soil samples were then cultured at dark for 30 days before used as the treatments of corn pot experiment. After corn harvest, soil acidity, cation exchange capacity, organic matter, available nutrient content, microbial diversity, plant aboveground and root growth and nutrient uptake were analyzed.

Results Compared to before sowing, the lateritic red soil pH after harvest of maize in RSD, RCK, PSD, and PCK treatment decreased by 0.11, 0.60, 0.92, and 1.04 unit, the decrease in RCK, PSD, and PCK reached significant level. While the latosol soil pH after harvest in RSD increased by 0.22 unit, and that in RCK, PSD, and PCK decreased by 0.13, 0.16, and 0.36 unit, with significant decrease in PSD and PCK treatment. In lateritic red soil, there were no significant differences among the four treatments in exchangeable H⁺ and Al³⁺ content, while in latosol soil, the exchangeable Al³⁺ in RSD treatment was higher than in RCK, but that in PSD lower than PCK. The soil cation exchangeable capacity (CEC) in the RSD and PSD treatments were significantly higher than that in the corresponding lime treatment. The RSD and PSD increased the soil CEC by 27.11% and 17.69% in lateritic red soil, and increased soil CEC by 10.10% and 6.40% in latosol soil, respectively. Both RSD and PSD increased the content of soil organic matter, available N, P and K significantly, compared with lime controls. The application of straw decayed products enhanced the species abundance of Firmicutes, Actinobacteria, Ascomycota and Basidiomycota, stimulated the growth of maize plants and roots and the absorption of nutrients. Compared with lime treatment, the plant height, biomass, total root length, root surface area and root volume of maize treated by pea straw decayed product increased by 59.51%, 738.43%, 280.00%, 392.87%, 404.31% respectively in lateritic red soil, and those in latosol were 29.82%, 72.04%, 23.43%, 11.05% and 5.79%, respectively.

Conclusions Compared with lime, the application of rice and pea straw decayed products effectively prevented soil re-acidification, improved soil fertility, increased soil microbial community diversity, and promoted the growth of maize. The promoting effect of pea straw decayed product was better than that of rice straw decayed product.