Farm Horizons, June 2018

New approach to N management

By Dave Schwartz
Certified crop advisor, Gold Country Seed

When I worked with the Extension Service 14 years ago, we hosted many crop meetings, and it’s surprising how many times nitrogen management was a topic of discussion.

Optimum nitrogen rates, fall vs. spring application, nitrogen management in continuous corn, and best management practices for N were discussed. We devoted a lot of time and resources to managing nitrogen in crops.

Now, in my current role as a seed dealer, I scout corn fields from July through September.

There are years where nearly all corn fields have adequate nitrogen levels, and then there are years when more than 50 percent of the fields show nitrogen deficiency symptoms. At winter meetings following harvest, we are back to the drawing board discussing how to manage nitrogen.

The optimum rate of nitrogen for corn changes each year, because each year, we are handed a different set of weather conditions.

I believe rainfall is the most important factor and it seems in recent years (if you believe in global warming), we have had more than one 50-year storm event. Big rains in late May and June can drive nitrogen down below the root system of corn plants. Corn plants’ root system is quite limited in May and early June, compared to plants at tassel.

So, in my mind, this nitrogen issue really boils down to managing risk, and maybe the old line about not throwing all your eggs in one basket applies here.

Research has shown that spring applications of nitrogen are a best management practice and have a yield advantage over fall applied nitrogen. If we rely on all spring-applied N and we have a late spring like we did this year, it may be difficult to get fertilizer on in a timely matter.

So, applying a small percentage of our N late in fall with a nitrogen stabilizer may have merit. Then, in spring, this land will be ready to plant.

On some of the remaining fields, it may be wise to plan to sidedress a portion of the N, especially fields that are prone to nitrogen loss. Examples would be sandy loam fields, or fields with low areas with poor drainage.

Sidedressing N is a low-risk system that will assure nitrogen is available when plants need it the most – 12 inches tall to tassel stage. Plants take up only 5 percent of the total N from emergence to V6 stage.

One other recommendation on sidedressing nitrogen is to incorporate it to at least 3 to 4 inches. This will make it more available to the plant if weather turns droughty in July and August. I really believe sidedressing nitrogen, on a portion of the corn acres, has merit and will keep corn plants green through early September.

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