The mechanisms underlying the reduction in aluminum toxicity and improvements in the yield of sweet potato (Ipomoea batatas L.) After organic and inorganic amendment of an acidic ultisol

Soil acidification limits crop and pasture production and leads to the degradation of agroecosystems. The dissolution of aluminum (Al) in acidic soils can lead to Al toxicity towards plants depending on the species of Al present, and can decrease crop yield. Different organic materials have been suggested to alleviate Al toxicity and increase the yields of important crops such as sweet potato (Ipomoea batatas L.). Therefore, soil solution was collected from different treatments in a field experiment to investigate how sweet potato yield responds to different Al toxicity levels. The Al species in the soil solution were characterized and the nutrient contents were determined to evaluate the efficacy of alleviating Al toxicity by making a single application of canola straw (CS), peanut straw (PS), commercial organic fertilizer (OF), lime, or alkaline slag (AS); and a combined application of AS with one of the three organic materials in an acidic Ultisol. The aims were to alleviate Al toxicity and increase sweet potato yields. The results showed that all the amendments significantly decreased (P < 0.05) the total Al, monomeric Al, monomeric inorganic Al, and Al3+ concentrations in the soil solution. The AS and lime applications were more effective at decreasing the concentrations of phytotoxic Al species in the soil solution than applications of the three organic materials alone, and the Al3+ concentration decreased to as low as 7 μM, which was similar to lime. The AS, in combination with PS or OF, was more effective than their respective sole applications in decreasing phytotoxic Al species. The combined applications increased nutrient contents, and enhanced nutrient uptake by sweet potato. The mitigation of soil Al toxicity and the increase in nutrient contents after fertilization improve crop growth and crop yields in acidic soils. The AS + PS and AS + OF treatments were the best amendments for acidic Ultisols.