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Fertilizing oats for yield and quality


November 30, 1999
By Bruce Barker

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For high-quality oat production, test weight is king, and too much nitrogen (N) can result in lower test weights. “We have seen declines in test weight once the fertilizer N rate goes above 55 pounds per acre. That has been consistent, especially if the weather turns dry in July and August,” says Agriculture and Agri-Food Canada (AAFC) researcher Bill May at Indian Head, Saskatchewan.

May has conducted research on oat agronomy during the past decade at Indian Head, and says that his trials comparing N fertilizer rates consistently point to that 55-pound per acre rate, except in the Red River Valley and on saturated soils where N leaching may be a concern. There, higher rates may be justified, but he does not have the research to make a recommendation under those conditions. 

Finding the sweet spot
As in other cereal crops, N response is tied to moisture. Higher moisture produces higher yield, to a point.  For a 100 bushel per acre crop of oat, the crop requires 97 to 117 lbs of N per acre. However, not all of that N has to come from fertilizer. Research by Ramona Mohr and Cynthia Grant at AAFC Brandon, along with May’s work at Indian Head, confirms that optimum yields are achieved when soil-plus-fertilizer N equals approximately 89 lbs of N per acre (100 kg of N per hectare). Optimum yields were usually achieved in the 40 to 80 kg per hectare (36 to 71 lbs per acre) applied N range.

Rates above this optimum level tended to cause yield decreases and crop lodging, similar to May’s findings at Indian Head.

More recently, May has looked at nitrogen response in oats on land that has been in long-term versus short-term no-till cropping. In these trials, he has again found that while oat yield increases with increasing N rate, test weight quickly drops off, especially if the land was in long-term no-till. Additionally, the short-term no-till treatment required approximately 20 lbs of N per acre more than the long-term no-till treatment to achieve a similar grain yield.

“If there is enough moisture to produce high yield, there will be enough moisture for additional N mineralization,” explains May. “Under these higher moisture conditions, if you put on high rates of N fertilizer, the oats may use the fertilizer N instead of extracting residual N from the soil with very little change in yield and a decrease in test weight. That’s why I generally recommend a maximum of 55 pounds per acre of N fertilizer.”

May says that oats also appear to be very good at scavenging and exploring the rooting area for soil-N. In a separate medic crop rotation trial, he found that residual N levels following an oat crop tend to be lowest compared to wheat or flax.

In May’s experience, oat growers should be aiming at applying 30 to 55 pounds of N per acre on good, fertile land. Whether they use the approach of 89 lbs of N minus soil test N, or just apply 30 to 55 pounds of fertilizer N, he says they are using much the same approach. “We are probably just splitting hairs. The first 30 pounds is the most important. You need that amount regardless of the soil test to ensure even and vigorous growth across the entire field since residual N can vary quite a bit as you move across a field. Generally, 30 to 55 pounds of fertilizer N seems to be the right amount to apply. Above that and you can decrease test weight and increase lodging,” May explains.