Early Soil Nitrate Trends after Wheat in 2022

Small grain harvest is well underway across the region, and soil testing is progressing quickly. Crop yields have varied from below average to exceeding expectations across the region and often in the same area. Planting date, summer temperatures, and rainfall (too little or too much) were major factors this year.

The major factors influencing the amount of residual soil nitrate-N after crops are:

1.     Nitrogen fertilizer rate: too high or too low
2.     Crop yield achieved: much lower or higher than expected
3.     Nitrogen losses: denitrification and leaching after too much rainfall
4.     Nitrogen mineralization from organic matter: cool or warm growing season

Seasonal weather is a large driving factor in the amount of nitrate-N in the soil profile. This changes from field to field and year to year. Early spring weather conditions were very wet across much of the region. In June and July, some areas continued to receive adequate to excess rainfall. Meanwhile, other areas received very little rain in the late growing season.

AGVISE has tested over 10,000 soil samples from wheat fields across the region. The table below indicates the percentage of soil samples in each soil nitrate-nitrogen category in several areas of Manitoba, Minnesota, North Dakota, and South Dakota. The data should give you a general idea of how variable residual soil nitrate is from field to field in each region. With such variable crop yields, there is quite a bit of variability in residual nitrate following wheat in the region. In drought-affected areas of Minnesota, North Dakota, and South Dakota, over 10 to 20% of soil samples have more than 60 lb/acre nitrate-N (0-24 inch soil profile) remaining after wheat.

What about Prevented Planting or unseeded acres?

For Prevented Planting or unseeded acres, the factors above plus some additional factors will affect the amount of residual nitrate-nitrogen:

1.     How long was water standing on the field?
2.     Was weed growth controlled, early or late?
3.     Was tillage used? How many times? How deep?
4.     Was a cover crop planted? What amount of growth was achieved?

When submitting soil samples from fields that were not planted, please choose “Fallow” or “Cover Crop” as the previous crop. This will allow us to send additional information on soil nitrate trends for unseeded and cover crop fields once we get enough data.

As the fall soil testing season continues, we will keep you updated. If you have any questions, please call our experienced agronomic staff. We hope you have a safe harvest and soil testing season.

 

Corn Growth and Development – Are we behind?

This article originally appeared in the AGVISE Laboratories Fall 2022 Newsletter under Southern Trends

The spring and early summer were very interesting to say the least. Spring rains continued well into late May and delayed planting for sugar beet, corn, and soybean throughout the southern region. By mid-May, many producers changed long-day corn maturities to earlier corn maturities. In the Benson, MN neighborhood, corn planting finally got underway around May 20 (60% planted) and near completion on June 5 (93% planted). Around the coffee shop, many people have commented, “How far behind is the corn crop in 2022?” So, let’s put some numbers to this question.

The High Plains Regional Climate Center has a nice growing degree day (GDD) calculator for simulations of corn growth and development (https://hprcc.unl.edu/agroclimate/gdd.php). I made a few GDD simulations for previous years, comparing 2022 with 2019 (a below-average GDD year) and 2021 (an incredible GDD year). As of mid-July, the 2022 growing season was 3 days ahead of 2019 (63 more GDD) and 9 days behind 2021 (182 fewer GDD). A corn plant takes about three days to make a new leaf when the corn plant is V12 and younger, so you can guesstimate that we were about 3 leaf stages behind 2021.

With the late spring planting window, many corn producers around Benson, MN opted for corn maturities about 6 to 8 days earlier than normal. If you compare an earlier 92-day corn maturity with a more typical 100-day corn maturity, the required GDD to blacklayer is 2207 and 2401 GDD, respectively. We generally accumulate 20-30 GDD per day in midsummer. If either corn maturity was planted on May 20, the estimated silking (R1 stage) date is July 21 for the 92-day maturity and July 25 for the 100-day maturity, a difference of four days. Similarly, the estimated blacklayer (R6 stage) date is September 18 for the 92-day maturity and October 12 for the 100-day maturity, a difference of 24 days. Toward the end of the growing season when fewer GDD are accumulated per day, the difference in maturity groups really starts to show. Warmer than average temperatures will shorten that difference, but only time will tell if the right decision was to plant earlier corn maturities.

Nielsen, R. L. The Planting Date Conundrum. Corny News Network, Apr. 2022. Purdue Univ., West Lafayette, IN. https://www.agry.purdue.edu/ext/corn/news/timeless/pltdatecornyld.html

To help drive home the point about planting date and final corn grain yield, I really like the graph from Dr. Bob Nielsen at Purdue University (figure above). Early planting does not always result in very high corn yield, and late planting does not always result in very low corn yield. In 2022, late planting will limit top-end crop yield potential, but the final crop yield could still be good as long as GDD accumulation remains above average. As always, Mother Nature will be the final determinant in setting the final crop yield.

Prevented Planting Acres? What to do for 2023

This article originally appeared in the AGVISE Laboratories Fall 2022 Newsletter

Good crop prices encouraged late planting beyond crop insurance deadlines, but additional June rainfall kept some producers from planting all their acres, leaving some unplanted fields or unplanted parts of fields. There are many questions about soil testing on these unplanted fields: When should you start soil sampling? What kind of residual soil nitrate-nitrogen amounts can you expect? The extremely wet soil conditions may have caused considerable soil nitrogen losses to leaching or denitrification. Through summer, warmer and drier weather added nitrogen through mineralization of soil organic matter. In addition, cover crops and any weedy growth will acquire nitrogen from soil. The amount of soil nitrate-nitrogen remaining for next year will depend on soil type, environment, and management factors, which vary from field to field and zone to zone.

Management Factors
• What was the crop grown in the previous year?
• What was the nitrogen fertilizer rate and application timing? Was it applied last fall?
• Did you do any summer tillage? More tillage promotes nitrogen mineralization.
• How was your weed control? Did the weeds get large and acquire substantial nitrogen?
• Did you plant a cover crop? Did the cover crop get incorporated later?

Environmental Factors
• Did excessive rainfall cause nitrate leaching on well-drained soils?
• Did excessive rainfall cause denitrification on poorly drained soils?
• Were summer temperatures warm? Warm temperatures promote N mineralization.

Soil testing on these unplanted fields can begin as soon as good quality soil samples can be collected after mid-August. There is no reliable way to guess how much residual soil nitrate may be present in these unplanted fields or unplanted parts of fields. Soil testing is the only accurate way to learn how much residual soil nitrate remains in the soil profile. To obtain the best information for nitrogen management, we recommend splitting fields into management zones for soil testing. The unplanted field areas can vary considerably from the rest of the field, which will skew the field-average soil test result and resulting nitrogen fertilizer rate.

Zone Soil Sampling and Variable Rate Fertilization: Optimizing profits

This article originally appeared in the AGVISE Laboratories Winter 2022 Newsletter

Farmers, like all business owners, are profit maximizers: things are good when revenue exceeds cost. Things are even better when the difference between revenue and costs is substantial. The math behind increasing profit is simple: reduce costs, increase revenue. But, the difficult part is finding and implementing strategies on the farm to do this. Why not start with fertilizer, which is typically the largest annual input cost on the farm?

Your fields are variable. You know the hilltops have lower crop yields than the mid-slopes, and you know exactly how far the saline spots creep into the more productive part of the field. So why use the same rate of fertilizer in the unproductive areas as you would in the productive areas? Optimize your fertilizer inputs by reducing rates in low-yielding areas and reallocate those fertilizer dollars to the productive ground.

The North Field Zone Map

Figure 1. North Field zone map, created using ADMS from GK Technology.

How does one actually do this? Creating zone maps for your fields, soil sampling and testing based on productivity zones, and variable rate (VRT) fertilizer application is the place to start. Applying VRT fertilizer allows you to apply fertilizer where it is needed and not waste fertilizer dollars where it is not. Let me show you an example from my family’s farm in western North Dakota.

I farm with my dad and brother in southwest North Dakota. This past fall, I created zone maps for each of our fields, with help from GK Technology and their ADMS program. The final maps are based on historical satellite imagery. I will show you one of our fields, the North Field, and take a deep dive on nitrogen fertilizer optimization using zone soil sampling and VRT fertilization in the dryland “out west” country.

The North Field (Figure 1) is variable. That is expected on a 120-acre field with many hills and ravines (Table 1). For discussion, we will use residual soil nitrate-nitrogen results and make a nitrogen fertilizer plan using urea for hard red spring wheat (HRSW) in 2022. You can see the soil nitrogen data, crop yield goals, and final nitrogen rates in Table 2.

 

The first place to optimize fertilizer inputs is setting realistic crop yield goals for each zone. Spring wheat yield goals range from 65 bushel/ acre in the best zone (zone 1) to 30 bushel/acre on the hilltops (zone 5). Adjusting the nitrogen rate for the proper crop yield goal ensures that the high-producing zones are not limited by lack of nitrogen (increased fertilizer cost, increased revenue) and the low-producing zones are not overfertilized (decreased fertilizer cost, same revenue). With a responsible crop yield goal on the low-producing zones, the crop still receives the amount of nitrogen it requires, and excess nitrogen is not lost to nitrate leaching (wasted input cost). As a result, the excess nitrogen fertilizer is reallocated to high-producing zones, resulting in more crop yield with the same total fertilizer budget, and increased revenue.

The nitrogen fertilizer scenarios in Tables 3 and 4 break down the projected revenues and expenses, demonstrating the benefits of zone soil sampling and VRT fertilization. For the North Field on my farm, the projected profit increase was $3,725 for the field or $31.05 per acre. It is tough to argue with a dollar amount like that! Prices will vary, of course, for fertilizer and precision ag services in your geography. Do the math for yourself and see how zone soil sampling and VRT fertilization can maximize profits for you.

2021 Drought: High residual soil nitrate-nitrogen across the region

This article originally appeared in the AGVISE Laboratories Winter 2022 Newsletter

The 2021 drought rivals the 1988 drought, and it covered much of the northern Great Plains and Canadian Prairies. From previous experience with droughts, we expected that residual soil nitrate-N following crops would be higher than normal, caused by the drought and reduced crop yields. The first wheat fields that were soil tested in August and September confirmed our expectation that residual soil nitrate-N was already trending much higher than normal.

The 2021 AGVISE soil test summary data highlights how exceptional the 2021 drought was. The median amount of soil nitrate-N across the region was markedly higher following wheat and corn. Over 20% of wheat fields had more than 100 lb/acre nitrate-N (0-24 inch) remaining, and another 40% of wheat fields had a sizable 40 to 80 lb/acre nitrate-N (0-24 inch) left over. For any given farm, the great variability in residual soil nitrate-N makes choosing one single nitrogen fertilizer rates impossible, and soil testing is the only way to decide that right rate for each field.

Through zone soil sampling, we were also able to identify that residual soil nitrate-N varied considerably within a field. This makes sense because we know that some areas of the field produced a fair yield, leaving behind less soil nitrate, while other areas produced very poorly and left behind much more soil nitrate. These differences across the landscape are driven by soil texture, soil organic matter, and stored soil water as well as specific problems like soil salinity or low soil pH (aluminum toxicity). Although the regional residual soil nitrate-N trends were higher overall, it is truly through zone soil sampling that we can begin to make sense of the field variability that drives crop productivity and the right fertilizer rate for next year.

For fields that have not been soil tested yet, there is still time to collect soil samples in winter (see winter soil sampling article). Nobody wants to experience another drought, but this kind of weather reminds us how important soil nitrate testing is every year for producers in the Great Plains. Each year, AGVISE summarizes soil test data for soil nutrients and properties in our major trade region of the United States and Canada. For more soil test summary data and other crops, please take a look at our soil test summaries online.

 

 

Controlling Soybean Cyst Nematode: Do you have a resistance problem?

This article originally appeared in the AGVISE Laboratories Winter 2022 Newsletter

This is the third year of our soybean cyst nematode (SCN) resistance project. Each year, we have flagged spots in soybean fields and collected paired SCN soil samples in June and September. If the SCN egg count increases through summer and into fall, we can quickly learn if the soybean SCN-resistance source, either PI88788 or Peking, is working or failing. University SCN surveys have found that the PI88788 resistance source has begun to lose its effectiveness at controlling SCN populations in much of Minnesota. This is a particular problem because 95% of SCN-resistant soybean varieties still use the PI88788 resistance source.

SCN egg count and soybean yield data from the 2021 AGVISE SCN resistance project. Bars of the graph represent SCN egg count, lines of the graph represent soybean yield. Click on the graph for a higher resolution version.

In 2021, paired soybean variety comparisons with SCN soil samples and soybean yield data really helped us see the difference in these SCN resistance sources. Among the sites, the Peking resistance source always had a lower SCN egg count than the PI88788 comparison, indicating that the Peking soybean varieties had better control of the SCN population at 4 of 5 sites. The Alberta site had similar SCN population control with both PI88788 and Peking resistance sources, so the soybean yield was similar at the site. However, the other sites demonstrated SCN resistance to PI88788, and the resulting soybean yield with the Peking resistance source was better with 7-bu/acre soybean yield increase on average.

For 4 of 5 sites, it is apparent that a Peking-traited soybean variety is the better choice. To learn if you have SCN resistance problems in your field, the simple early-late SCN soil sampling exercise, like we did in this project, is a quick way to learn if your current soybean variety is still controlling SCN and delivering the best soybean yield.

 

 

How much residual soil nitrate is left after the 2021 corn crop?

It’s probably more than you think.

So far, the residual soil nitrate-nitrogen trend following corn is much higher than average across the upper Midwest and northern Great Plains. This follows the same trend set by the 2021 wheat crop. For many growers in the region, the hot and dry growing season has resulted in high residual soil nitrate-N carryover where corn yield was lower than average. An update on average residual soil nitrate-N after grain and silage corn, broken into zip code areas, can be found below (Table 1). This data highlights the importance of soil sampling for nitrate-N, even after high N-requirement crops you may not think of leaving much residual soil nitrate-N behind.

Bar graph showing median residual nitrate-N in lb/acre for fields sampled after grain corn as of Oct. 11, 2021. Results include fields tested in MN, ND, SD, and MB. Fields tested thus far are on pace to set a record for amount of nitrate-N left after corn.

The early soil nitrate-N trend data gives us a snapshot of the soil samples that AGVISE has analyzed so far. The average soil test data is not a replacement for actual soil test results on your fields or your clients’ fields. There is considerable variability within a single zip code area, with some corn fields having less than 20 lb/acre nitrate-N and many other fields that are much higher. Take a look at eastern South Dakota, the Sioux Falls and Watertown areas have over 49% of soil samples with more than 100 lb/acre nitrate-N (0-24 inch soil depth). Considering sky-high nitrogen fertilizer prices (and still rising), it makes sense to soil test for nitrate-N and credit it toward next year’s crop nitrogen budget.

Agronomic considerations for soybean in 2022

One crop that will not benefit from extra residual soil nitrate-N after corn is soybean. Soybean can create its own nitrogen thanks to a symbiotic relationship with nitrogen-fixing bacteria. The nitrogen fixation process takes energy, however, and if there is already ample plant-available nitrate in the soil, soybean will delay nodulation and take advantage of the free nitrate. Delayed nodulation may ultimately lead to soybean yield loss.

High residual soil nitrate-N can also increase soybean iron deficiency chlorosis (IDC) severity.  Soybean IDC is a challenge for growers in the upper Midwest, northern Great Plains, and Canadian Prairies, especially on soils with high carbonate and salinity. If soil nitrate-N is also high, research has shown it can make soybean IDC even worse and result in lower soybean yield. If you plan to grow soybean on fields with high residual soil nitrate-N, seriously consider IDC-tolerant soybean varieties or consider planting them on fields with lower residual soil nitrate-N.

Should a corn-corn rotation be considered after a drought year and high soil nitrate?

Planting a second corn crop would allow a producer to capture this “free” nitrate-N in the soil profile. However, planting corn on corn has many challenges from soil moisture to insect pressures (e.g. corn rootworm). The 2021 corn crop started the growing season with a full profile of water (due to excessive moisture in 2019 and adequate moisture in 2020) and ended with enough to push the corn crop through harvest. Going into the 2022 growing season, plant available water will be considerably less than the beginning of 2021. If the drought continues into 2022, remember that corn requires more moisture than soybean, so planting corn on corn means putting a higher water-requiring crop on ground that had less water to start with (versus corn following soybeans). Less available moisture, combined with other agronomic pressures, may mean less than expected yield for a corn-on-corn rotation.

Table 1. Residual nitrate trends as of Oct. 11, 2021 from more than 2,500 soil samples taken after corn. Regions with less than 60 soil samples are not included in the table.

Corn Stalk Nitrate Test

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

for corn stalk nitrate test article

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

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).

Brent Jaenisch Joins AGVISE Technical Support Team

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.