Effects of soil,grass and legume root extracts on heterotrophic bacteria,nitrogen mineralization and nitrification in soil

The effects of root extracts of four grasses and two legumes and extracts of soils supporting these plants on the growth of five strains of heterotrophic soil bacteria, and on the rate of nitrogen mineralization and nitrification were measured in culture and in soil. All the root extracts inhibited the growth in culture of the five bacteria by 9–98 per cent. The legume-soil and one of the grass-soil extracts did not inhibit bacterial growth. Only two of the grass-soils, Andropogon lectorum and Pennisetum purpureum markedly inhibited the five bacteria. Incubation of soils with extracts of grass roots or grass-soil increased the rates of nitrogen mineralization and nitrification and incubation with legume root and soil extracts increased the rates of nitrogen mineralization and nitrification even further.