Timing of Manure Injection and Nitrification Inhibitors Impacts on Nitrous Oxide Emissions and Nitrogen Transformations in a Barley Crop

Mitigating the greenhouse gas emissions that arise during the use of livestock manure is a crucial environmental challenge. We evaluated the management effects of liquid manure timing (fall vs. spring) and nitrification inhibitors (NIs) [2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) vs. 3, 4-dimethylpyrazole phosphate (DMPP)] on N2O emissions, soil mineral N transformations, barley (Hordeum vulgare L.) productivity, and N uptake. Eight treatments were established in an incomplete split-plot design in Lacombe and Edmonton, AB, Canada. Repeated measurements included N2O fluxes by manual static chambers, and soil ammonium (NH4-N) and nitrate (NO3-N) concentrations. Relative to the manured soils without NIs, the use of NIs with fall injection significantly reduced annual N2O emissions by 81% with DMPP and 58% with nitrapyrin in our Lacombe site; however, this difference was not found in the comparable spring treatments applied during the dry growing season. These beneficial effects were discernable in Lacombe, which was relatively wetter than Edmonton, indicating the overriding role of varying moisture on N dynamics and fluxes. Following a 5-mo freezing winter, the spring thaw caused at least 64% of annual N2O emissions from the fall-manured soils, and these intense episodic fluxes also revealed that the efficacy of fall-added NIs still continued during the early spring. On average, fall injections amplified the N2O direct emission factors by about threefold compared with the corresponding spring treatments. Thus implementing liquid manure injections with NIs at the right timing has the potential opportunity to increase N uptake by crops and simultaneously diminish global warming effects.