Using inhibitors to trade greenhouse gas emission for ammonia losses in paddy soil: A zero-sum game

Nitrogen (N) amendment of soil ecosystems alters GHG fluxes to the atmosphere by increasing nitrous oxide (N2O) emission and affecting methane (CH4) uptake in well-aerated soils. Although nitrification inhibitors (NIs) can decrease N2O emission, this may alter the rate of ammonia (NH3) volatilization, crop yield, and soil CH4 fluxes by directly or indirectly affecting methane-oxidizing bacteria, causing severe environmental and economic damages. Here, we measured the response of gaseous N loss (N2O + NH3) and GHG fluxes (CH4 + direct N2O + indirect N2O) to the intensive application of three different rates of DCD (15 to 45 kg ha−1) and DMPP (3 to 9 kg ha−1) in N fertilized soils imposed upon six different rice cultivars. N addition increased NH3 volatilization by several orders of magnitude, N2O emission by 7- to 10-fold, and CH4 emission by 2- to 4-fold. DCD and DMPP strongly inhibited the N2O emission and, to a lesser extent, CH4 emission but promoted greater NH3 losses in a dose-dependent manner. The soil receiving urea with inhibitors exhibited up to 62.7% additional NH3 volatilization than untreated (inhibitor-free) soils over the rice growth cycle. Considering the estimated indirect N2O emission from deposited NH3, the overall inhibitory effect of nitrification inhibitors (at different application rates) ranged from 17.4% to 36.6% (reduction) for global warming potential and -6.7% to -45.9% (increase) for nitrogen losses. Collectively, our results suggest moderate inhibition of global warming potential but inadequate reduction of gaseous nitrogen losses by NIs, which were outweighed by increased NH3 volatilization. Consequently, NIs appear to be a potentially double-edged sword when targeting to diminish gaseous nitrogen losses from N fertilized soils.