Corn is Sprinting: Does it need nitrogen?

It is the time of year that the corn crop is beginning to sprint.

It is hard to find corn in the Northeast that was not planted under suitable conditions. With few exceptions, the majority of the corn planted has received ample amounts of precipitation and growing degree days this year.

Physiologically, corn is close to or at the time of exponential growth. The plant needs a balance of nutrients all season long and that need changes throughout the season. As we approach this exponential growth period, the demand for nitrogen moves from steady to very steep on the demand curve.

Determining nitrogen need

Setting your corn crop up with its seasonal need for nitrogen is no small task. Things like the impact of current and past field management practices, organic and inorganic nutrient amendments (manure, composts, manufactured fertilizers, etc.), variety, plant population, and weather can all help predict nitrogen need. However, there are other seasonal factors, like weather, that must be considered as well.

Not all corn needs to be side-dressed with nitrogen. Crop sequence along with pre-season and annual organic nutrients help determine what corn will benefit from additional nitrogen. Experience and the literature tell us that applying nitrogen close to the time of high demand, V8-10 or sprinting time, brings an economic yield advantage. 

When determining nitrogen needs, historical perspective can be a good place to start. Farmers that have previously harvested crops on a field have a very good sense of what to expect each year as a new crop begins. However, yield in a field can vary significantly, or not at all, from year to year.

Scouting and evaluating the crop for several weeks post-planting can help us account for any variation and determine where the plants are in the growing stage. Scouting can provide insight on variations in planting performance from year to year. It can also help account for factors that are out of our control, such as weather.

Feed the need

We know that applying nitrogen, when warranted, at the time of maximum crop uptake is a yield winner. Accounting for variation, we can fine-tune application rates. We can also drill deeper to adjust that rate for different areas in a field. Field biomass is assessed, production areas are assigned, and the application equipment places nitrogen according to the production area.

Now the areas of a field have nutrients based on expected yield potential. The nitrogen is put where it will have the greatest impact on yield and return, and not wasted on areas it’s not needed. This helps reach not just a higher yield potential, but also a higher quality product. The economic impact of this approach is twofold; we can better control our environmental footprint and increase the profitable yield per acre or per cow.

How does it work?

It starts with an NDVI (natural difference vegetative index) image of the corn field just prior to max nitrogen uptake. NDVI is an index of near-infrared and infrared light reflectance from the corn that is well correlated to biomass. Field zones are made based on similar NDVI and the ability of the application equipment to manage those areas.

NDVI is derived from a color infrared image.
Color infrared image.

In most cases, the result is three to four distinctive zones in a field. Pounds of supplemental nitrogen is assigned based on yield potential and the existing nitrogen supplying power occurring in the different zones. A nitrogen rate prescription is made specific to the computer in the application equipment which is linked to the GPS (global positioning system) on said equipment. As the machine navigates the field the rate applied changes accordingly to the zone the machine is in.

Using past experiences, data, and technology, we can put nutrients exactly where they’re needed for the biggest economic impact. We know this because we can measure the impact these adjustments to application rates have on yields. A harvest monitor can measure the effect different application rates had on different parts of the field. If you don’t have a harvest monitor, similar observations can be made through scouting, tissue sampling, and soil sampling.

Taking the time to look through the data before and after nutrient application yield short- and long-term benefits. In the short term, we can improve this year’s crop. In the long term, we can start to plan for next year’s by adjusting things earlier in the cycle, such as prescriptive seed rates.

The Dairy One Precision Farming team has helped many farms determine optimal nitrogen rates this season. The team has the tools and expertise to help you get the most out of this year’s crop and begin to plan for an even better crop next year. To find out more, email [email protected] or call 607-252-7550.


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