Denitrification under different cultivated plants: effects of soil moisture tension, nitrate concentration, and photosynthetic activity

Abstract

Plant effects on the denitrification rate were investigated in pot experiments at different soil moisture tensions and nitrate concentrations. Nitrate concentrations and the soil moisture tension were regulated immediately before each measurement. The effects of the plants on denitrification rates were dependent on the soil moisture tension. At a low soil moisture tension (−7 cm H2O), there was a 10-fold increase in the denitrification rate (planted versus unplanted soil). At a medium moisture tension (−30 cm H2O) the plants had practically no effect, and at the highest tension (−60 cm H2O) the effect was slightly negative. Large differences in denitrification rates under different plant species were observed. At a low soil moisture tension, the average denitrification rate (μg N kg−1 soil h−1) was 39–42 under small grains (barley, wheat, and oats), 47–82 under the grasses (cocksfoot, meadow grass, meadow fescue, and timothy) and 18 under red clover. The differences between the monocots were attributable to differences in plant growth rates, rather than to any specific difference in stimulation or inhibition of denitrification, since the variations in photosynthetic activity fairly well predicted the differences in denitrification rates under different monocots. Clover, however, gave much lower denitrification rates than those predicted by the photosynthetic activity.