Our frequent rainfalls and wet soils are creating difficult circumstances to provide sidedress nitrogen applications to corn. Nitrogen is a key nutrient in determining corn yield. Unfortunately, there is limited capability for the soil to store nitrogen, dependent mainly upon soil organic matter content so generally supplemental nitrogen is needed to produce an economical yield. The nitrogen in organic matter has to be converted to an inorganic form to allow plant roots to absorb and utilize the nitrogen. Synthetic, commercial fertilizers provide nitrogen in a readily available inorganic form. The issue is that once nitrogen is in the inorganic form, primarily as a nitrate ion, it is very susceptible to loss. The main avenues of loss involve water; either nitrogen leaching through the soil profile and beyond the reach of plant roots with high and/or frequent rainfall events, or through denitrification in standing water/saturated soil conditions when the nitrate ion is converted to the nitrite ion and lost as a gas back into the atmosphere.
Ideally, a commercial nitrogen application is applied a close as possible to the time when the corn plant demand for nitrogen is greatest from V-8 growth stage to tassel. The longer nitrogen must wait around before the crop uses it, the greater the chance it can move and be lost before the crop needs it. This is why agronomists typically refer to nitrogen as a “leaky” nutrient. This week I am excerpting comments from some OSU Extension specialists including Steve Culman, soil fertility specialist and Peter Thomison, corn production specialist regarding their thoughts on what to do about nitrogen fertilizer for corn in this difficult 2019-growing season.
“The excessive water this spring has clearly driven nitrogen losses in many fields, but how much? Recent research at Ohio State has shown that ear leaf N, soil nitrate and grain yields were significantly reduced after just 2 days of standing water in the field. So N losses can occur quickly with excessive water.
A perfect indicator of N need does not exist, but some tools can help. Crop sensing tools like NDVI meters or crop sensing aerial imagery can provide insight if they are used routinely. Soil-based tests can also monitor N availability. Soil nitrate is the most widely available and vetted test. A value of 25 ppm or higher indicates that there is sufficient N. More information can be found here: https://agcrops.osu.edu/newsletter/corn-newsletter/2017-20/manure-psnt-and-n-recommendations. Ongoing research at Ohio State is looking to develop soil health indicators that can provide insight into how much N will be available over the growing season.
Corn typically takes up less than 1 pound/ acre of N before the V4 stage, but N uptake rates will increase dramatically through tasseling. N uptake does continue beyond tasseling and into grain fill, but at much lower rates. Research at Ohio State and Purdue has shown that if sidedress applications are not made due to saturated conditions, rescue N fertilizer applications can increase yields and reduce the negative impact of flooding. Note these responses are much more likely to occur in fields that had high N loss conditions (excessive water).
How much N should be applied? This is a difficult question to answer, it’s important to keep in mind that yield potential of corn can be severely restricted by excessive stress in the early phases. But corn that has simply grown too tall to sidedress might not have been severely stressed and yield potential could still be good. The potential of N loss and the extent of stress should be considered when determining N rates. It’s also important to consider the likelihood of economic return to invested N fertilizer. This economic model is used to maximize farmer profitability: http://go.osu.edu/corn-n-rate
The choice of N source will likely be driven by application equipment, but best practices for minimizing N losses should be considered and practiced if at all possible. Consider that N losses can increase as the growing season progresses and soil and air temperatures rise. For example, if broadcasting with urea, consider a stabilizer such as Agrotain to minimize volatilization losses.”
Rory Lewandowski is an OSU Extension Agriculture and Natural Resources Educator and may be reached at 330-264-8722.
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