Study pinpoints worst time for fertilizer emissions

Three years of field experiments with fertilizer impacts and greenhouse gas emissions in Saskatchewan indicate plans to reduce emissions must target early spring. The experiments from 2014 to 2016 with varying spring, fall and split fertilizer applications showed little difference in impacts, soil scientist Richard Farrell from the University of Saskatchewan told an irrigation meeting in Moose Jaw.

The split application before planting and during the growing season saw fewer emissions after the second application because “growing plants take up all the nutrients.” Increased or decreased fertilizer application rates did not have much impact on emissions.

Most of the emissions came after spring thaw as residual fertilizer nitrates were pulled out of the soil. Between 50 per cent and 80 per cent of emissions were after spring thaw.

“It starts at snow melt and goes right up until two days before crop is seeded.”

Non-irrigated site emissions were much lower. Irrigated sites have more crop residues, higher fertilizer application rates and “over time develop microbial systems that are almost looking for nitrogen to form nitrous oxide so you get higher emissions because of the history of the site.” The emissions were worst during one dry year when unused nitrates accumulated in greater quantity. Two of the years were wet, he said.

Different yields did not change emissions.

The experiment was conducted to see if fertilizer application impacts were at odds with environmental goals. No data was kept on costs of the different procedures. The process involved what Farrell called the “4Rs” of nutrient stewardship: right source, right rate, right time and right place.

Both urea and anhydrous ammonia fertilizers were used.

Ron Walter can be reached at ronjoy@sasktel.net