PSNT – Champlain Valley Crop, Soil & Pasture

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).

Applying nitrogen to corn, a process known as side-dressing.

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.

Pre-sidedress nitrogen test samples at the UVM
Agricultural and Environmental Testing Lab.

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
leaching).
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

By Kristin Williams, Agronomy Outreach Professional

We just finished a two-year, multi-farm study on the health of clay soils, funded through a VT Conservation Innovation Grant through the NRCS. Measures of soil health (using Cornell’s soil health test) were not consistent, and we found that comparing practices over time was more informative than comparing field to field. One interesting, and maybe
obvious, lesson was the correlation between soil health practices and crop yields.

So, how do soil health practices influence yield? Research suggests soil health can improve yields. It is important to note our project focused on demonstration, not replicated research. We compared no-till and conventional/reduced till corn silage on 5 farms with clay fields in our region. A simple t-test revealed no significant difference in yield between no-till (19.1 tons/acre) and conventional (19.2 tons/acre). More importantly, we were able to demonstrate that a farmer can grow no-till without yield losses, and be successful with good management practices. A yield gain might take time as the soil builds up its condition.

We also wondered how cover crop species or mixes might affect corn silage yield. We had an opportunity to use a field where the corn was accidentally killed. We planted 15 different combinations, including 4 single species, 6 two-way mixes, and 5 three-way mixes. This project was a slight anomaly in that the cover crops were planted with a drill in late August, which allowed for a more vigorous production of all cover crops. Radish was a star in the fall, maximizing both phosphorus and nitrogen uptake. We did not measure phosphorus content in the spring, so we do not know how much was retained in the soil. It seems to have allowed
for more available nitrogen in the soil at the time of a pre-sidedress nitrogen test (PSNT), therefore requiring less nitrogen. Surprisingly, legume mix covers had good fall biomass, but that did not translate into more N mineralization.

We applied nitrogen to each plot as per the PSNT recommendation for 20 tons/acre corn silage. At the end of the season, we measured corn silage
yield and compared that to nitrogen applied (see graph). The winter rye plot had a lower corn silage yield and required more nitrogen. Other than the nutrient effect of less uptake and slower decomposition, there may have been a physical barrier created by the standing rye crop, which was particularly vigorous in the spring. However, our three-way mix (winter rye – oats – radish) actually had the highest average corn silage yield, even though it required more N at PSNT time than the pure radish stand.

So, do not go abandoning your winter rye just yet. In fact, we think this three-way mix has promise and we are looking for a mix that gives both fall and spring soil conservation. Radish alone will winter kill, which may be good for mineralization, but not as good for spring soil conservation. Oats also winter kill but provide faster fall soil cover than rye by itself.

When using an over-wintering cover crop, it is clear that timing and success of termination is critical for subsequent crop yields. Nitrogen mineralization may happen later in the season with a plant such as winter rye that has a heavier carbon content. In a no-till system particularly, you may need to adjust your nitrogen rates/timing and put more on upfront. If you are using cover crops, a PSNT seems like a wise investment.

It is also important to remember that soil health is a long game, and it may take time to see the results of your labors with cover crops. We have replicated this project by replanting these cover crops in the fall of 2016, this time planted in September, and will look at this again this coming season.

More info about UVM’s PSNT test can be found at:
go.uvm.edu/getpsnt