Three ways to maximize nitrogen this growing season

Rock River Laboratory
Taking advantage of the array of nitrogen analyses can maximize fertilizer while input prices climb.

Fertilizer and commodity prices are in constant flux and the weather never seems to run on the desired schedule. The silver lining is that opportunities to improve efficiencies, and thus profits, exist - and sometimes they are simple management efforts that can extend positive effects throughout the growing season.

One such tool is nitrogen testing. Three soil tests and two tissue tests – all for nitrogen - can be used to optimize dollars spent. It’s important to know how each of these tools can amplify crop potential, as well as the pitfalls that can occur if used incorrectly.

Preplant and Presidedress

Timing and sample collection technique are the most important distinctions among the various nitrogen tests on the market.

“With the soil tests, the actual analysis that happens at the laboratory is the same for each test we offer,” explains Dustin Sawyer, laboratory director and soil scientist with Rock River Laboratory.

The difference, he says, is in how the results are interpreted. The interpretation of the Preplant Nitrogen Test (PPNT), for example, requires that samples be collected at two depths in each site: one at zero to twelve inches and another at twelve to twenty-four inches. Meanwhile, the Presidedress Nitrogen Test (PSNT) requires only a zero to twelve-inch sample.

“Nitrate is the form of nitrogen that the plants prefer, so knowing how much is in the soil is key to optimizing growing conditions that can be controlled,” advises Sawyer. “More important still is knowing how much is in the soil at the time that fertilizer is being applied.”

He adds that timing is critical to the success of nitrogen testing. “The nitrogen cycle is quite active during the growing season, so nitrogen can change form rapidly as it gets cycled through the microbial community.”

The microbes are still active in soil samples after they’ve been collected, so it’s important to arrest their activity quickly so as not to alter the sample post-collection. If the sample cannot be processed by the laboratory within 24 hours of collection, the best practice is to freeze the sample.

“Don’t wait too long to get the sample to the lab as the nitrogen cycle is still happening in the field,” warns Sawyer. “If you wait, let’s say a week, before laboratory delivery, that sample is no longer a representation of the current field conditions.”

Tissue Analysis

Tissue analysis is another option to manage nitrogen during the growing season, and there are two options: in-season and post-season. “In-season tissue testing is a great way to be sure that the nitrogen that was placed in the soil is actually getting into the plant,” explains Sawyer.

Timing, soil moisture, excess rain, and application error all affect the expected yield response – which is based on nitrogen application. Sawyer recalls that there has been at least one occasion in which tissue analysis has shown that the fertilizer spreader was missing strips in the field.

“While such realities are not fun for a grower to uncover, at least it was discovered while there was still time to take corrective action.” Without tissue analysis, such setbacks likely wouldn’t have been uncovered.


Post-season tissue analysis is used a bit differently than the aforementioned nitrogen tests. Rather than providing information to correct the growing crop, this test scores how well the nitrogen was managed in this year’s crop, to outline changes to nitrogen management in next year’s crop.

Requiring some very specific sampling protocols in order to be useful, the post-season tissue sample incorporates the eight-inch section of corn stalk that begins six inches above the soil surface. “Imagine running a tape measure from the soil surface up the corn stalk and marking the corn stalk at six inches and fourteen inches,” explains Sawyer. “The lab needs those eight inches between the marks.” 

As with the other tests, timing is crucial. This test, known as the Late Season Corn Stalk Nitrate Test, needs to be conducted one to three weeks after the onset of Black Layer.

When it comes to spending money wisely, there is no substitute for information.

“These are tested and proven analytics that provide insight into the actual crop need for additional inputs,” says Sawyer. “It surprises me that more people don’t take advantage of them.”

In a year when limiting input costs is crucial, finding cost-effective, simple means to make decisions that maximize potential seems like a platinum lining.