Corn growers could save on fertilizer costs by taking more advantage of the organic nitrate nitrogen in their soil.
“Most farmers have a substantial bank of nitrogen in the soil, but it’s in the organic fraction,” says John Heard, a Manitoba Agriculture soil fertility specialist.
“The difficulty is for us to predict in advance when it’s going to come out.”
Traditional soil tests can help Manitoba growers determine nitrate levels before fertilizing and seeding. Generally, these tests have served growers well.
However, sometimes there is a tremendous release or mineralization of nitrogen from organic matter, Heard said, resulting in little benefit from applied fertilizer nitrogen.
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The hitch is that the availability of the organic nitrate nitrogen to the crop can vary greatly from year to year and is so unpredictable that farmers cannot afford to underfertilize in anticipation of a large nitrogen release. Soil moisture, temperature and oxygen all have an influence, as do soil microbe populations.
Heard said some corn growers in the American Midwest are trying to make the most of their soil’s organic nitrate nitrogen by using a split application of nitrogen.
They first learn how much fertilizer nitrogen should be applied based on traditional nitrate soil tests. Rather than applying all of that nitrogen at seeding, they apply only a portion to establish the crop.
The soil nitrate levels or plant chlorophyll content are then reviewed in early June, giving growers an idea of how much organic nitrate nitrogen is being freed up for the crop and whether they need to apply the full balance of fertilizer recommended before planting.
This approach opens the possibility of cutting back on fertilization in years when conditions bolster the amount of organic nitrate nitrogen released to the crop, Heard said.
“If we can estimate the amount of nitrogen that has been freed up by the soil at that time, we can do some fine tuning of nitrogen rates.”
Heard, who spoke at the Manitoba Corn Growers Association’s corn school, held in Winnipeg Feb. 21, said time constraints of a short growing season on the Prairies are an obstacle. So is availability of equipment to side dress fertilizer.
Another strategy involves soil testing to determine the amount of organic nitrogen that might be metered out over the season. Soil test companies are developing several new chemical tests.
Use of the conventional nitrate soil test can also be improved, Heard said. During a two-year research project recently completed by Manitoba Agriculture and the Manitoba Corn Growers Association, conventional soil test samples were taken from zero to 15 and 15 to 61 centimetre depths.
In one instance, a deeper sample detected sufficient nitrogen in the 0.6 to 1.2 metre depth to meet the crop’s nitrogen needs.
Heard said growers who follow highly fertilized crops on sandy soils may wish to check this depth because corn will be rooting to this extent later in July. He cautioned that his ideas come with risks, the greatest being lost yields from trying to second guess Mother Nature.
He said growers may want to spend more on the knowledge and on-farm testing side of their operations.
For example, rather than spending $40 per acre on nitrogen, a producer might instead benefit by spending $10 per acre on a professional crop scout, who could then work on strategies to bring the fertilizer costs below $30 an acre while still getting equivalent or better yields.
