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.

Understanding high residual soil nitrate-nitrogen following drought

Soil testing after small grains is well underway, and we are seeing higher than normal soil nitrate-nitrogen levels, as expected. Crop yields have varied from much below average to surprisingly decent in some locations. It is easy to understand why residual soil nitrate-nitrogen is high in fields where the 2021 drought was severe and crop yield was very low. It is a little harder to understand how some fields, that produced decent crop yields, can also have higher than normal soil nitrate-nitrogen as well. Given the variability we are seeing across the region, the only way to know whether or not your fields have higher-than-expected residual soil nitrate-nitrogen or not is to sample and test these fields.

We will attempt to answer some of the questions about “Where did all the soil nitrate-nitrogen come from?” and “What should we do next year?” farther down.

2021 Residual Soil Nitrate-Nitrogen Summary, Early Report (First 6,500 Fields)

AGVISE has tested over 6,500 soil samples from wheat fields across the region so far. We usually wait to share the early soil nitrate-nitrogen summary until September, but we have been getting a lot of questions already. The table shows the average soil nitrate-nitrogen (0-24 inch soil profile) and the percentage of soil samples in each category for several areas of Manitoba, Minnesota, North Dakota, and South Dakota. As you can see, there is considerably more residual soil nitrate-nitrogen than the long-term average of 30 to 45 lb/acre nitrate-N in a good year. In some areas, over 30 to 50% of soil samples have more than 80 lb/acre nitrate-N (0-24 inch) remaining after wheat.

Reasons for high residual soil nitrate-nitrogen in a drought with low crop yield

  • Lower crop nitrogen uptake and use (low crop yield)
  • No soil nitrogen loss from leaching or denitrification
  • Warmer than average soil temperatures in the early growing season when soil water supply was better, resulting in above nitrogen mineralization from soil organic matter (can be 40 to 100 lb/acre N)
  • Nitrogen fertilizer near the soil surface was positionally unavailable because there was no soil water for plant roots to obtain it

Where did high residual soil nitrate-nitrogen come from in fields that had decent crop yields?

In 2021, crop water use demanded a lot of stored soil water uptake from deeper in the soil profile. If the crop was able to root down deep enough and fast enough, the crop found additional water in the subsoil along with nitrate-nitrogen from previous years. With the extra water and nitrate found in the deep subsoil (below 24 inches), the resulting crop yield surprised many farmers and agronomists. Just because we do not routinely collect soil samples below the 24-inch soil depth in most areas does not mean there is zero nitrate-nitrogen down there. After a series of wet years, the amount of nitrate-nitrogen that can accumulate in the lower soil profile can be considerable. In a drought year, when all crops were forced to root deeper just to survive, the deep nitrate-nitrogen makes a significant contribution to the total plant nitrogen uptake.

What about the nitrogen fertilizer that was applied last spring and all the nitrate-nitrogen in the topsoil (0-6 inch soil profile)?

With the very dry topsoil conditions, plant roots grew deeper in search of water. Since plant roots obtain most nitrate-nitrogen through mass flow in soil water, this situation left fertilizer nitrogen “stranded” and positionally unavailable near the soil surface. Although this was bad for this year’s crop, the “stranded” nitrogen is in a good position for next year’s crop. We experienced the same phenomenon in 2017 and 2018, after some areas had experienced a severe drought. There were fields with decent crop yields and considerable “stranded” nitrogen, just like this year.

Strategies to utilize high residual soil nitrate-nitrogen for next year

With so many wheat fields with high residual soil nitrate-nitrogen this fall, you may want to consider changing your crop rotation. Severe droughts like 1988 and 2021 are not very common, so we need to think outside the box. It is common for wheat to be followed in the crop rotation with a legume like soybean or dry edible bean. However, the drought has left you with a lot of residual soil nitrate-nitrogen, and nitrogen fertilizer prices are staggeringly high right now. If you have 100 lb/acre nitrate-N (0-24 inch soil profile), that is $60 per acre of “free” nitrogen fertilizer at current urea prices ($550/ton). In addition, excess soil nitrate-nitrogen can also make soybean iron deficiency chlorosis (IDC) worse on moderate to high IDC risk soils. Do you want to sacrifice $60 per acre of “free” nitrogen AND risk lowering soybean yield due to more severe soybean IDC?

Drought can be sporadic or continue for multiple years. You may want to consider more short-season crops in the crop rotation that require less water and can produce well in drier years (remember, we used most of the stored soil water in 2021). Short-season crops to consider include winter wheat, spring wheat, durum wheat, barley, canola, etc. It is also important to consider the current price for each crop. With high crop prices right now and promising futures prices in 2022, you could lock in some good prices for next year. Although two consecutive years of the same crop (e.g. wheat) is not ideal for disease management, there was very little disease in 2021, and it might allow some different weed control options for future crops in the rotation. All in all, a drought brings opportunities to think outside the box.

 

Lessons (Ghosts) of Droughts Past

From Alberta to Iowa, the region has experienced everything from abnormally dry soil conditions to exceptional drought. In some places, the drought started in 2020 and has continued through 2021. Considering lower than expected crop yields, we expect that residual soil nitrate-nitrogen levels will be much higher than normal in many wheat, canola, and corn fields this fall. There was reduced crop nitrogen uptake and little to no soil nitrogen losses to leaching or denitrification through the growing season, which should result in higher soil test nitrate-N remaining in the soil profile.

In major drought years, high residual nitrate levels are a normal phenomenon. In 1988, the average soil nitrate test following wheat across the region was a staggering 107 lb/acre nitrate-N (0-24 inch soil profile). This is considerably higher than the long-term average around 30-45 lb/acre nitrate-N (0-24 inch soil profile). The 1988 drought was extreme, and 2021 has rivaled that in some locations. Based on previous drought years, it will be no surprise to find wheat fields with 80-100 lb/acre nitrate-N (0-24 inch soil profile) or even higher.

Past experience also shows us that drought can create greater crop yield variability across fields. Some zones in the field with better water holding capacity and soil organic matter may have produced a decent crop yield, and these will have lower residual soil nitrate-N. Yet, other zones may have had very poor crop growth and yield, leaving very high amounts of soil nitrate-N remaining.

Zone soil sampling is always a good idea, but it is especially important in drought years. Soil sampling based on productivity zones is the only way to determine the correct amount of nitrogen fertilizer in each zone across the field. To create good productivity zones for soil sampling, it is best to use multiple data layers such as satellite imagery, crop yield maps, topography, or electrical conductivity (Veris or EM38).

This fall, we expect residual soil nitrate-N to be higher than normal, but there will be exceptions to the rule. Last spring, there was a lot of broadcast urea fertilizer applied without incorporation. If no rain was received for several weeks after application, much of the nitrogen could have been lost to ammonia volatilization. This means some fields will seem out of place with lower residual soil nitrate-nitrogen because fertilizer nitrogen was lost last spring.

For fields with more than 150 lb/acre nitrate-N (0-24 inch soil profile), the crop nitrogen requirement for next year may not call for much, if any, nitrogen fertilizer. We must remember that drought creates variability within a field and even within large productivity zones. This is why we always suggest applying a base amount of nitrogen fertilizer to address the variability, even if the soil nitrate test is more than 150 lb/acre nitrate-N. A base nitrogen fertilizer rate (maybe 20 to 40 lb/acre N) should address most of the field variability and provide a fast start to the next year’s crop. In 1988, we learned the tough lesson that applying no nitrogen fertilizer on fields testing very high for nitrate-N was a mistake, and the best producing parts of fields had early-season nitrogen deficiencies. A modest base nitrogen fertilizer rate was the right decision to cover field variability.

Three Simple Lessons from Droughts Past

  1. Soil test all fields for residual soil nitrate-N. There will be considerable variability from field to field and even zone to zone.
  2. The residual soil nitrate-N test allows you to reduce nitrogen fertilizer rates for next year, saving money on crop inputs for 2022.
  3. Remember to apply a modest base nitrogen fertilizer rate on fields testing very high in nitrate-N to address field variability. You will want to get next year’s crop started right.

Save Time and Avoid Mistakes by Using AGVISOR to Submit Soil Samples Online

AGVISE Laboratories is always trying to make soil sampling easier. Since 2011, AGVISE customers have enjoyed submitting soil samples online through our AGVISOR platform. AGVISOR is the online platform that allows you to submit soil samples (conventional, grid/zone, and soybean cyst nematode samples); save grower and field information (so you don’t have to fill it in by hand on paper forms); and set default crop fertilizer guidelines. With online submission, you simply submit the sample information online and print barcode reference number stickers to place on each soil sample bag (like below). There is no more handwriting on soil sample bags or forms anymore!

Picture of samples with online sticker labels for AGVISOR article

With the online AGVISOR platform, organizing your sampling operation is easy. You can save time by submitting soil samples ahead of time and printing reference number stickers before the fall soil sampling rush begins. If you are working with a third-party sampler, you can submit samples online and then email a PDF of the barcode reference stickers to the sampler, allowing them to print the stickers at their location.

In addition to submitting samples online, the AGVISOR platform allows you to view, print, and save soil test reports. This means you can save soil test reports and send them as PDFs to growers. AGVISOR also allows you to change crop choice, yield goal, and fertilizer guideline type (broadcast vs. band). The flexibility of the platform makes it easy to keep up with changes that inevitably happen in farming.

If you have any questions on how to access AGVISOR or need help navigating the online submission and results platform, please give one of our Laboratories (Northwood 701-587-6010; Benson 320-843-4109) a call and our technical staff will be happy to help you.

How Much AMS Does Your Spray Water Need?

AGVISE Laboratories Spray Water Analysis

Hard water is a fact of life for those of us in the northern Great Plains and Prairie Provinces. It is why our homes have water softeners, why our well water tastes funny (or delicious), and one reason we need to add AMS (ammonium sulfate) or UAN to our spray tanks to optimize weed control.

When we talk about conditioning “hard water” for herbicide applications, we are preventing dissolved salts (calcium, magnesium, sodium, potassium, and iron) in water from antagonizing, or binding, the pesticide we’re putting in the tank. Dissolved salts bind to weak-acid, salt-formulated pesticides and reduce their efficacy (e.g. glyphosate [RoundUp], growth regulators, ACCase inhibitors [Select, Axial, etc.], ALS inhibitors [Pursuit, Express, etc.], HPPD inhibitors [Callisto etc.], and glufosinate [Liberty]).

A water conditioner like AMS prevents salts in spray water from binding to pesticides. AMS is most often recommended at rates from 8.5 to 17 lb/100 gal spray volume on herbicide labels. This is a wide window, however, and handling dry AMS can be a pain. So, how do you know how much AMS you should add to the tank to overcome antagonism?

A spray water analysis!

An example of an AGVISE Laboratories spray water report

AGVISE Laboratories provides fast and convenient analysis of spray water used for pesticide applications. The Spray Water Analysis package includes calcium, magnesium, sodium, iron, pH, salt, hardness, and SAR (sodium adsorption ratio). The spray water report uses NDSU data to determine the recommended amount of AMS required per 100 gallons of water to overcome antagonism. You will want to test each water source you use for pesticide applications. This information can help avoid problems throughout the spraying season.

Give us a call in either Benson, MN, or Northwood, ND and we will send you a water sample kit. Each kit contains a water collection jar and a sample information sheet. Water sample tests are completed within a week and results are emailed to you, so you have information on your water source right away.

Don’t let salts take away from your weed control this summer – get your spray water tested!

2021 Plant Nutrient Deficiency Troubleshooting Project

Plant analysis is a valuable tool for managing plant nutrients and troubleshooting agronomic problems. Being certain that a specific plant nutrient is causing deficiency symptoms is difficult with visual symptoms alone. Many causal agents unrelated to soil fertility can cause symptoms that appear to be nutrient-related. There are also some plant nutrient deficiencies that are impossible to determine visually so we call them a “hidden hunger.” For troubleshooting situations, you will need a pair of good and bad plant samples, along with good and bad soil samples, to discover the real answer to what is happening in the field (nutrient deficiency or something else).

To help you troubleshoot problem areas and get familiar with plant analysis, AGVISE Laboratories is sponsoring the Plant Nutrient Deficiency Troubleshooting Project in 2021. We are looking to work with 50 to 100 customers this summer who see apparent nutrient deficiency symptoms in one of their fields and want to be involved in this educational project. Volunteering in this project will help you figure out if a problem area in a field is caused by a plant nutrient deficiency or something else. If you want to volunteer, contact one of our agronomists or soil scientists in Northwood (701-587-6010) or Benson (320-843-4109) as soon as you have a problem area you want to troubleshoot for this project. Immediacy is key for good data. The results may be inconclusive if you wait to take plant samples 7 to 10 days after symptoms first appear because new problems can arise.

Once you have spoken with one of our staff and described the problem in your field, we will send you the supplies packet to submit good and bad plant samples, as well as good and bad soil samples (0- 6 inch). If you can provide us with good photographs to aid in the problem diagnosis, we will cover the soil and plant analysis fees (two complete tissue analyses and two complete soil analyses; $151.20 USD retail value).

It is important to catch plant nutrient deficiencies early while you still have time to make a rescue fertilizer application. Take advantage of the AGVISE Plant Nutrient Deficiency Troubleshooting Project and solve those problems the right way… right away.

New Address for AGVISE Laboratories Canada Receiving Facility

The AGVISE Laboratories Canadian Receiving Facility has moved across the street from its former location in Winkler, Manitoba. What this means for customers sending samples to our Canadian Receiving Facility:

  • The new address is 380 Kimberly Rd Winkler, MB R6W 0H7
  • If you’ve dropped off samples at the receiving shed in Winkler, the shed is now across the street in the Winkler Construction parking lot
  • We will be changing the address on all future printings of AGVISE documents, such as Purolator shipping labels
  • If you have pre-printed Purolator shipping labels that have the old address (375 Kimberly Rd), you can still use these. The Purolator delivery professional knows where the shed has been moved to. 

If you have any questions, please give us a call at 701-587-6010.

Soil Testing and 4R Nutrient Stewardship

Each year, farmers aim to increase agricultural production and profitability while conserving our land resources for the next generation. These tandem goals drive sustainable soil fertility and crop nutrition decisions on cropland across the world.

In 2005, global fertilizer industry and environmental stakeholders began developing a standard theme to emphasize science-based stewardship in soil fertility and crop nutrition. The theme eventually became known as 4R Nutrient Stewardship, where each “R” referred to the “right” way to manage nutrients for crop production. The 4Rs are summarized as managing crop nutrition with the 1) Right Source, 2) Right Rate, 3) Right Time, and 4) Right Place.

To successfully implement 4R Nutrient Stewardship, you must start with a high-quality soil sample and an informative soil test. To begin, the fertilizer need and amount is determined through soil testing, which is based on regionally calibrated soil test levels for each crop. If you do not have a soil test, how do you know what the Right Rate is? Using crop removal rates or simply guessing without soil testing often leads to overapplication of fertilizer, cutting into profit.

A conventional whole-field composite soil sample (one soil sample per field) is certainly better than no soil sample. It gets you in the ballpark, but it does not detect variation in soil nutrient levels across the field. You might underapply fertilizer on high yielding parts and overapply fertilizer on low yielding parts. To get the Right Rate applied in the Right Place, precision soil sampling, either grid or zone, is the best way to determine the appropriate fertilizer rate and where to apply it in each field. Precision soil sampling is a proven tool to reduce over- and under-fertilization across fields, thus optimizing crop yield and profitability while reducing the potential risk of soil nutrient loss to the environment.

When you start soil sampling and making soil fertility plans for next year, keep 4R Nutrient Stewardship in mind. AGVISE Laboratories is a proud 4R Partner. To learn more about the 4Rs or become a 4R Partner, visit the 4R Nutrient Stewardship website.