Amelioration of an acid ultisol by agricultural by-products.

Ultisols are widely distributed in the subtropical regions of China as well as in the world. High acidity of Ultisols limits plant growth and reduces crop yields. Amelioration of an acid Ultisol was investigated by incorporating the residues of canola ( Brassica campestris L.), wheat ( Triticum aestivum L.), rice ( Oryza sativa), corn ( Zea mays), soybean ( Glycine max), peanut ( Arachis hypogaea), faba bean ( Vicia faba L.) and pea ( Pisum sativum) and Chinese milk vetch ( Astragalus sinicus L.) shoots after incubation of the agricultural by-products for a maximum of 75 days, soil pH was increased by each of the plant materials. The degree of amelioration of the soil acidity by the plant materials was found to depend on the ash alkalinity and N content of the materials; the legumes of higher ash alkalinities and lower N contents, such as peanut straw and faba bean straw, led to the largest increases in soil pH, while the legumes of higher N contents showed less amelioration of the acidity to a certain degree, because of the release of protons during nitrification of NH [ABSTRACT FROM AUTHOR]