Effect of Lime and Organic Matter on Soybean Seedlings Grown in Aluminum‐toxic Soil

Abstract Organic matter is believed to be able to reduce Al toxicity in Ultisols. Since little information is available to substantiate this hypothesis, a greenhouse experiment was conducted to compare the effects of organic matter and lime on soybean [ Glycine max (L.) Merr.] plants grown under increasing Al stress in a Bradson (Typic Hapludults) soil. Treatments, replicated three times, were 0, 25, 50, and 100 mg Al kg −1 pot −1 , 0, 5, and 10% wheat ( Triticum aestivum L.) straw, and the equivalent of 0, 1, and 2 Mg CaCO 3 ha −1 . After thorough mixing and incubation of the growth medium at field capacity for 20 d, five soybean seeds were germinated per pot and the five seeds allowed to grow for 30 d. The results indicated that shoot and root growth were severely affected by increased Al treatments. Aluminum toxicity started to seriously affect plant growth at 50 mg Al kg −1 , and plants were hardly growing at 100 mg Al kg −1 . However, plant growth in the Al‐toxic soil was improved substantially by the application of wheat straw or lime. The data suggest that treatments with wheat straw produced taller plants and greater dry weight contents of roots than was found in plants grown only with lime. Lime alone yielded good results, but lime in the presence of organic matter was more effective in reducing the effect of Al toxicity. The plants receiving wheat straw still contained relatively high levels of Al (3.7–7.4 mmol kg −1 ) in their shoots, but little damage could be detected. A tendency toward a decrease in N content was noticed in shoots of plants grown in the presence of wheat straw, but this was believed to have been caused by a temporary immobilization of N because of the application of straw. It was concluded that organic matter was as effective as lime in reducing Al toxicity.