ONTARIO GRAIN FARMER ENVIRONMENT 25 continued on page 26 rain – as much as 7.5 centimetres (3 inches) – is needed to avoid this problem. And if urea is broadcast on wet soils, volatilization starts immediately. “Even if it rains three days later you can lose a lot,” Nasielski says. TO INHIBIT, OR NOT? Volatilization inhibitors are widely regarded as an effective go-to tool for increasing the longevity of nitrogen fertilizer. However, in some cases, their use has been proven to actually hurt the bottom line. “If you’re applying any nitrogen on the surface, urease inhibitors will significantly reduce losses from volatilization,” Nasielski says. “This was consistent at every site location every year. But they are much more economically beneficial if you’re using urea compared to UAN because UAN already has much less loss.” Applying 50 pounds of urea per acre, plus an inhibitor at $0.125 per pound of urea, provides an average return of $14 per acre more (assuming corn is priced at $4.50 bushel). Applying the same rate of UAN, with an inhibitor costing $0.105 per pound of fertilizer and the same average corn price, also returned about $14 per acre. There were notably more cases where the additional cost of the inhibitor incurred financial losses when added to UAN, though. In an era of sky-high fertilizer costs, research helps growers identify efficiencies to maximize profitability “Sometimes we weren’t getting high losses with UAN, so net returns could have been negative. But I think overall, if you’re surface applying urea or UAN, the net returns are going to be positive,” Nasielski says. UREA IS SAFE TO TOP-DRESS Yield penalties from fertilizer whorl and leaf burn were also analyzed. In experimenting with what Nasielski calls the worse case scenario – 160 pounds of urea or UAN directly entering the whorl of corn plants across one acre – yield impact was not observed at or below 5 per cent damage. Above that, yield potential starts dropping at half of 1 per cent for every additional per cent of leaf burn. Six per cent damage to the canopy, that is, will incur half of one per cent drop in relative yield. Similar losses to yield potential begin once 15 per cent of the surface area of ear leaves are burned.
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