28 Our Advertisers Appreciate Your Business Better Farming | July/August 2024 APPLYING NITROGEN ping season is that MERN varies significantly across years, depending on weather conditions, which are unknown beforehand. Nasielski says that some farmers will apply more than they need to in order to compensate for environmental N losses, with the logic being that rainfall could leach some N away. “I understand this thought process, but it doesn’t always work that way. Generally, losses increase the more N that is applied,” Nasielski says. Environmental optimization Avoiding N losses can not only help improve profitability, but also reduce environmental impacts, Elgie says. He warns that overapplication of N poses significant environmental risks. At rates higher than MERN, uptake of additional N fertilizer decreases, and every additional kilogram of N has a higher potential for loss. “Excess N is prone to losses via volatilization, leaching, and denitrification,” Elgie says. “In Western Canada, the leaching is less of a concern,” adds Hammermeister, “but there can be denitrification losses, and depending on the moisture circumstances, it might be a small loss (or) quite a significant loss.” Denitrification leads to losses of nitrous oxide (N2O), a powerful greenhouse gas, approximately 298 times more potent by weight than CO2, Elgie says. For its part, the federal government wants to see N2O emissions from farms reduced 30 per cent by 2030. Although Ottawa’s goal isn’t mandatory, Hammermeister worries that that might change if the sector faces years when farmers are powerless to stop Mother Nature from forcing N losses. One way to mitigate that or avoid overapplication in typical years is to determine the right rate. Soil testing is key, but they’re not all equal or the same, and the wrong test could miss N mineralization, causing overapplication of N, which would then get released into the environment. Elgie explains that as microbes break down soil organic matter, N is released in a process called mineralization. Measuring this mineralization can be done by collecting a Pre-Sidedress Nitrate Test (PSNT), the results of which can assist in finetuning N application rates, Elgie says. Hammermeister points out PSNT hasn’t been used in grains and oilseeds in Western Canada because that region’s “100-day” crops grow too aggressively early on. Elgie also recommends 4R practices, such as split-application, injection or incorporation of N fertilizers, and use of N stabilizers such as urease or nitrification inhibitors, to reduce N losses. Explains Weersink: “Splitting application allows one to assess growing conditions and adjust rates accordingly. Inhibitors slow the release of N so its availability better matches the needs of the crop and less is lost.” Birch Effect Complicating N management decisions in Western Canada have been recent droughts and/or very dry falls and their impact on how soil biology mineralizes organic matter. In scientific literature, the process is beginning to be nicknamed the “Birch Effect” after a researcher who started publishing his observations back in the 1950s. Hammermeister explains that when soils go through an extended period of drying, there are some physical and biological changes that occur that can result in a N mineralization burst. Triggering the burst is warm soil and moisture. “The degree of nitrate release relates to the duration of the drought and the organic carbon (OC) content of the soil. The greater the drought duration and the greater the OC content of the soil, the greater the mineralization potential,” Hammermeister says. Portions of Western Canada have seen consecutive dry growing seasons and/or very dry falls the last few years, and the Birch Effect is resulting in a large release of nitrogen from fields that have been in zero-till for 15 to over 30 years, he says. “If farmers are not accounting for this plant-available nitrogen, they could easily be over-fertilizing their crops to the detriment of yield, profitability, and the environment,” Hammermeister says. BF Chart provided by OMAFRA YIELD NITROGEN RATE N Loss Yield N LOSSES Maximum Yield MERN NITROGEN RATE INTERACTION WITH YIELD AND LOSSES Theoretical nitrogen rate interaction with yield and N losses. As N rate increases above MERN, less N is taken up by the plant, leading to higher rates of loss. note that MERN occurs at a lower N rate than maximum yield. NITROGEN RATE INTERACTION WITH YIELD AND LOSSES
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