By Rico Balzano, Agronomy Outreach Professional
Spring 2017 started relatively dry, but Mother Nature has certainly made up for it, with above average rainfall in May, and the seventh wettest June in 100 years (National Weather Service, Burlington, VT).
While this spring’s rainfall may average out to be normal, the timing of it has caused some problems. Rain started to increase just as corn planting season began, keeping soils cold and postponing planting. Cold soils delayed emergence and slowed growth in planted fields. More to the point, nitrogen fertilizer that was applied pre-plant or at planting time has seen extremely susceptible to loss. Nitrogen is lost through denitrification in saturated soils, and is lost through leaching in well-drained soils. Either way, nitrogen is often not there when the corn needs it. This will prompt many farmers to think about applying nitrogen to corn while it is growing, a technique known as sidedressing, which is a more efficient
use of nitrogen, especially on soils prone to leaching.
The good news is that the organic nitrogen in manure has been slow to mineralize because of the cool temperatures and will still be there as the season progresses. However, it is safe to say many farms will be sidedressing corn with extra nitrogen this year.
The old, reliable way to predict how much sidedress nitrogen to apply is the pre-sidedress nitrogen test (PSNT). PSNTs are simple and affordable ($6-8). However, they require effort and only offer a snapshot in time; they do not account for previous activity nor for future nitrogen mineralization.
An alternative way to generate sidedress recommendations is Adapt-N software. Nitrogen is very dynamic in the soil so it is difficult to predict how much will be plant-available. Therefore, it is necessary to have as much information as possible about fertilizer, manure, previous crop and soil type to generate a good recommendation with Adapt-N. You can also assess the nitrogen needs of corn using chlorophyll meters, active sensors and aerial imagery. These can be effective when used properly, and local agricultural consultants can provide these services.
PSNT is recommended for corn fields 2 or more years after a sod, and/or where manure rate is uncertain, or if manure application is not expected to meet corn N requirement. PSNT is not recommended in first-year corn after a grass sod; first-year corn after an alfalfa grass stand is plowed down; or if enough manure was applied to meet corn N requirement.
Below are the PSNT sampling guidelines, a link to the UVM sample submission form, and the updated UVM nitrogen recommendations
based on PSNT results. Results are usually sent out within 24 hours since the information is time-sensitive.
PSNT Sampling Guidelines:
1. Wait 2-3 days after significant rainfall (due to nitrate
2. Sample when corn is 6-12” tall and sample to a depth of
12” – deeper than a regular soil test.
3. Take 15-20 cores per field from in between rows to avoid
fertilizer bands. Mix sample thoroughly.
4. Air dry samples ASAP to stop further mineralization.
5. Submit samples in small plastic bag (about 1 cup).
Download the PSNT Form: go.uvm.edu/psntform
N Recommendations: go.uvm.edu/nitrogenrecs
More Info: go.uvm.edu/getpsnt