Alfalfa saponins and microbial transformations of nitrogen in peat

Alfalfa saponins, their sugar fraction or glucose, but not their sapogenin fraction, favored nitrogen immobilization and denitrification and inhibited proteolysis and ammonification in both peatinoculated and Pseudomonas sp.-inoculated media. Alfalfa root saponins and sapogenins significantly reduced the fungal peat population, but did not affect the bacterial population. The inhibition of N mineralization in peat by saponins and by their sapogenin fraction during dry and wet cycles was mostly due to their fungistatic activity. The inhibitory effect of the sugar fraction of alfalfa roots on mineral-N accumulation in peat is mainly under moist conditions.