Alfalfa roots and nitrogen transformations in peat

Accumulation of NH⁺₄ and NO^-₃ in peat was significantly reduced by living or decaying alfalfa roots. Alfalfa root extracts, alfalfa saponins, the carbohydrate fraction of alfalfa saponins and mono- and disaccharides inhibited NH⁺₄ production and NO^-₃ accumulation, in a casein-amended peat or enrichment cultures, and they enhanced denitrification in a flooded peat. NO^-₃ accumulation in peat was affected to a lesser extent by polysaccharides, the genine (aglycone) fraction of alfalfa saponins, and by the root extracts of Rhodes grass, clover and wheat. It is suggested that inhibition of accumulation in alfalfa-grown peat is mainly due to the relatively high concentrations of free sugars and saponins of alfalfa roots, which lead to NH⁺₄ immobilization, with a concomitant decrease in NO^-₃ accumulation.