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

Abstract

Nitrogen (N) amendment of soil ecosystems alters GHG fluxes to the atmosphere by increasing nitrous oxide (N 2 O) emission and affecting methane (CH 4 ) uptake in well-aerated soils. Although nitrification inhibitors (NIs) can decrease N 2 O emission, this may alter the rate of ammonia (NH 3 ) volatilization, crop yield, and soil CH 4 fluxes by directly or indirectly affecting methane-oxidizing bacteria, causing severe environmental and economic damages. Here, we measured the response of gaseous N loss (N 2 O + NH 3 ) and GHG fluxes (CH 4 + direct N 2 O + indirect N 2 O) 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 NH 3 volatilization by several orders of magnitude, N 2 O emission by 7- to 10-fold, and CH 4 emission by 2- to 4-fold. DCD and DMPP strongly inhibited the N 2 O emission and, to a lesser extent, CH 4 emission but promoted greater NH 3 losses in a dose-dependent manner. The soil receiving urea with inhibitors exhibited up to 62.7% additional NH 3 volatilization than untreated (inhibitor-free) soils over the rice growth cycle. Considering the estimated indirect N 2 O emission from deposited NH 3 , 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 NH 3 volatilization. Consequently, NIs appear to be a potentially double-edged sword when targeting to diminish gaseous nitrogen losses from N fertilized soils. • N fertilization significantly enhanced the emission of NH 3 , CH 4 and N 2 O. • Higher inhibitory effect of DCD and DMPP for N 2 O than CH 4 fluxes. • DMPP exhibited a similar inhibitory effect to DCD at five-fold low application rates. • NIs appear to be a double-edged sword in diminishing gaseous nitrogen losses.