Soil pH changes after application of plant shoot materials of faba bean and wheat

In a soil incubation experiment, the effect of green material of faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) on soil pH was compared. I n comparison with control, the application of both plant materials caused a significant soil pH increase. The liming effect was higher for faba bean t han for wheat. This difference in liming effect between the two plant speci es was closely related to their alkalinity concentration. In total, 82% of the alkalinity in faba bean and 96% of that in wheat were water-soluble. To elucidate possible factors responsible for the difference in liming effect , plant matter of wheat and faba bean was fractionated and organic anions w ere identified. The total concentration of identified organic anions was co mparable for both plant species. For wheat, over 80% of the alkalinity occu rred in the form of simple organic anions with malate as the dominant one. In faba bean, only 40% of the alkalinity was identified as simple organic a nions. About 40% of the alkalinity were related to macromolecules, possibly pectinates. Our data suggest that macromolecules such as pectinates may be mainly responsible for the greater liming effect of faba bean, as compared to wheat.