Evidence for nitrification ability controlling nitrogen use efficiency and N losses via denitrification in paddy soils

For understanding the effects of nitrification ability on nitrogen (N) use efficiency and N losses via denitrification in paddy soils under flooding conditions, six paddy soils with different nitrification activities were sampled from various sites of China and a pot experiment was conducted. Rice plants at tillering stage were transplanted into pots and harvested 7.5 days after transplanting, 15N-(NH4)2SO4 was applied 2.5 days after rice transplanting under continuously flooding conditions. The N losses by denitrification were determined by the unrecovered 15N applied as 15NH4 + and the N use efficiency (NUE) was calculated by 15N taken up by rice plants. Plant height (from 33.8 to 37.3 cm) and biomass (from 1.07 g pot−1 to 1.52 g pot−1) increased significantly with the native NH4 + concentration in the studied soils (P < 0.01). The NUE decreased, whereas the N losses via denitrification increased due to the increase in the nitrification rate of soils determined at 60% water holding capacity (P < 0.05). The results implied that the nitrification activity of paddy soils is a key factor in controlling NUE and N losses via denitrification.