27 Story Idea? Email Paul.Nolan@Farms.com Better Farming | July/August 2024 sponse to N, yields increase at a decreasing rate until a maximum yield is hit, and then it essentially plateaus. “It does not tend to fall within a reasonable range. While yield may not be lowered with rates beyond that associated maximum yield, it is not profitable to do so,” Weersink says. Agronomist Josh Nasielski adds that for corn, taking up N costs carbon (or sugar). The plant needs to expend photosynthate to assimilate it from the soil to a usable form. Corn won’t expend energy taking up much more N than it needs: It normally has a small reservoir of N, but the amount is small, he says. “So, from the perspective of more is better, the corn plant itself may not even be using the extra N that was applied,” Nasielski says. This leaves excess nitrate in the soil, which is vulnerable to losses to the environment, notes Saskatchewan agronomist Edgar Hammermeister at Western Ag Professional Agronomy. He adds that what’s underappreciated and largely not understood is the back side of the N yield response curve, where each additional pound of N starts taking away from yield. How steep that decline is relates to a growing season’s weather conditions. For instance, in a wet season, crops could experience lodging if they’ve been overfertilized. “The implication of the kinked stems is moisture and nutrients can’t be delivered to fill the kernels, resulting in a poorer quality crop,” says Hammermeister, who also notes the greater harvesting challenge. In a dry season, however, overfertilizing could result in “haying off,” particularly in the brown soil zones of Saskatchewan and Alberta. Haying off refers to a crop growing too aggressively at the start of the season, and thereby depleting its water reserves before it can set yield. Having provided such a crop more N than it needed could amplify those effects. Economic optimization “From a farmer perspective, there’s a loss of profitability, because he’s spending money on inputs that aren’t necessarily going to give him a return on investment,” Hammermeister says. Elgie explains that the ideal scenario is to choose the rate of N where $1 of input equals $1 of output, at a point known as the Most Economic Rate of Nitrogen (MERN). Applying N at a rate higher than MERN means spending more in fertilizer input than you will make up for in yield, he says. “While maximum yield may be the focus of yield contests, it may not be in the best interest of the farm business to target that maximum yield with relation to their N rate decision,” Elgie says. “Nitrogen fertilizers are expensive inputs, and excessive use can reduce the return on investment of these products.” Weersink notes that one dilemma for farmers trying to determine optimal rates at the beginning of the cropAPPLYING NITROGEN
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