Richard Jenny

Corn Stalk Nitrate Test

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To help evaluate nitrogen management in corn, you may want to try the corn stalk nitrate test as a post-mortem tool. The corn stalk nitrate test is a late-season or end-of-season plant analysis on mature corn stalks. Iowa State University developed the corn stalk sampling protocol and interpretation. If corn did not have sufficient nitrogen, the corn stalk nitrate level will be low. If corn had excess nitrogen, the corn stalk nitrate level will be high.

The corn stalk nitrate test can be useful in cropping systems with manure or corn-after-alfalfa, where a significant portion of the crop nitrogen budget comes from nitrogen mineralization. It is also helpful in more humid climates, where the residual soil nitrate-nitrogen test is not utilized. For corn silage production, it is easy to collect corn stalk samples on the go during silage harvest, making it a quick and useful tool.

Since the corn stalk nitrate test is a post-mortem tool with the goal to provide information for future years, it is not recommended in years with abnormal precipitation. In drought years, potential crop productivity is reduced, so the plant nitrogen requirement is lower than normal. In high precipitation years, soil nitrogen losses will reduce the available nitrogen supply. As a result, the corn stalk nitrate level can be very high in drought years or very low in wet years. Such results say more about environmental conditions, not the adequacy of the nitrogen fertilizer program.

When to sample

  • Early: One-quarter milk line (R5 growth stage) on majority of corn kernels. Nitrate concentration may be high if collected early.
  • Optimum: One to three weeks after physiological maturity (black layer, R6 growth stage) on 80% of corn kernels.
  • Late: Up to harvest. Nitrate concentration may be low if rainfall has leached nitrate from plant material.

How to sample

  • Measure 6 inches from the ground, cut the next 8 inches of corn stalk (the 6-14 inch stalk section measured from plant base). Remove outside leaf sheath.
  • Collect 12 to 15 corn stalks.
  • Place corn stalks in a ventilated plant tissue bag. Do not use plastic or zipped bag.
  • Do not collect diseased or damaged corn stalks.

Table 1. Corn Stalk Nitrate Test Interpretation

Nitrate-N (NO3-N), ppm Interpretation Comment
<250 Low Nitrogen supply was likely deficient and limited corn grain yield
250-2000 Sufficient
>2000 High Nitrogen supply exceeded plant requirement

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Jodi Boe

Updated Residual Soil Nitrate Trends (Variability is high this year)

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The 2022 growing season may seem like a long way off, but spring will be here before we know it. In fact, many growers are already making (or have made) crop choices and seed variety decisions for 2022. One factor that must be considered when making crop and variety selections for 2022 is residual soil nitrate-nitrogen following the 2021 growing season. For many in the northern Great Plains and Canadian Prairies, the 2021 growing season was hot and dry, which resulted in high residual soil nitrate levels following many crops. An update on average residual nitrate levels after wheat, broken down by geography, is below (Table 1). Residual soil nitrate-nitrogen following other crops, including soybean, are also higher than average (Table 2). This highlights the importance of soil sampling, even after crops we do not typically think of leaving high residual soil nitrate behind.

The data in the tables represents a snapshot of the samples we have tested so far this fall. While the average residual soil nitrate-nitrogen for an area may be interesting to talk about, it is not a replacement for actual soil test results from you or your growers’ fields. The data shows that over 30% of the wheat fields in many areas (see the right-hand column of the table) test over 100 lb/acre soil nitrate (0-24 inch depth). Droughts like 1988 and 2021 are very uncommon and leave us in situations that we are not used to dealing with. Using an average soil nitrate level from a region to decide an N rate on an individual field would be like deciding to apply an insecticide on every acre of the farm without even looking at each field to see if the insect is present. You need actual soil test data on each field to make informed decisions.

Table 1. Residual nitrate trends as of Sept. 17, 2021 from more than 20,000 soil samples taken after wheat. Regions with less than 100 soil samples are not included in the table.

Table 2. Residual nitrate trends as of Sept. 17, 2021 for crops other than wheat. Regions with less than 100 soil samples for each respective crop are not included in the table.

High Fertilizer Prices

According to the September 15, 2021 DTN fertilizer price survey, retail fertilizer prices continue to rise. The average price per pound of nitrogen by fertilizer product is $0.61/lb N for urea, $0.46 lb/N for anhydrous ammonia, and $0.66/lb N for UAN-28. This represents a 55%, 73%, and 71% increase in price compared to prices for the same fertilizers this time last year. Long story short, fertilizer is expensive. High residual soil nitrate following wheat may help reduce input costs in 2022, as long as you know what the residual soil nitrate in your fields is and take advantage of it by growing a crop that requires nitrogen fertilizer. If you have a soil nitrate test of 80 lb/acre (0-24 inch) after wheat, that is about 50 lb more than normal carry over. The extra 50 lb/acre soil nitrate is worth $30.00/acre (based on the current urea price).

Jodi Boe

Brent Jaenisch Joins AGVISE Technical Support Team

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AGVISE Laboratories is proud to announce that Brent Jaenisch has joined the AGVISE team as an Agronomist. Brent provides sales and technical support to AGVISE customers throughout Minnesota, South Dakota, and the northern Corn Belt. You will soon see his contributions in AGVISE newsletters and seminars. Brent is based at the Benson, MN laboratory.

Brent is a Minnesota native and grew up on a diversified grain and livestock operation outside Maynard, MN. Brent took his passion for farming and agriculture to school, obtaining a degree in Agronomy from the University of Nebraska-Lincoln, then a M.S. and Ph.D. in Agronomy from Kansas State University. Brent’s master’s degree research investigated wheat yield response to different fertilizer treatments and varying agronomic practices. His doctoral research evaluated wheat management practices in Kansas where he spent countless hours surveying wheat growers across Kansas and understanding the contribution of wheat yield components to wheat yield.

Brent enjoys interacting with agronomists and farmers, and has extensive experience leading and instructing research teams. Brent spent three summers of his undergraduate experience interning with CHS and Winfield in Minnesota, where he built lasting relationships with growers and retail agronomists. During his graduate school career, Brent trained, coordinated, and lead teams of new agronomists to complete field work and research tasks across the state of Kansas, which is no small feat!

Brent’s practical approach to agronomy, passion for teaching, and knack for building meaningful relationships make him an excellent addition to the AGVISE technical support team. We are excited to have him on the team and can’t wait for you to meet him.