John Breker

Troubleshooting Problems with Plant Analysis

in , , /by

A green growing crop is a delightful sight, and it is used by many people as an indicator of crop nutrient status. If you have fields with some yellow areas or slow growth, these symptoms may indicate a nutrient deficiency. Most commonly, yellow-looking plants may be deficient in nitrogen, sulfur, or both. If detected early, there may still be time for rescue treatment.

Plant analysis is not a magic or foolproof tool, but it can provide useful information in diagnosing problems when combined with soil analysis and good field scouting. During the summer, our technical staff receives many questions from agronomists, crop consultants, and farmers on troubleshooting problems in their fields. The following tips and tricks will help you identify potential nutrient deficiencies early.

Troubleshooting nutrient deficiencies based on visual symptoms can be difficult if symptoms look similar (yellow for nitrogen and sulfur deficiency in the early season) or indistinct (slow growth for phosphorus deficiency). Proper troubleshooting requires you to collect paired plant and soil samples from the area with poor plant growth and an adjacent area with good plant growth. A single plant sample from the poor area is seldom enough information to accurately identify the nutrient deficiency. A soil sample from the same area is needed to determine if the soil nutrient supply is truly lacking or if reduced plant nutrient uptake is caused by another factor (e.g., soil saturation, soil compaction, cool temperature, disease).

With paired plant and soil samples from both good and bad areas, you can compare the results and determine if the symptoms are caused by one or more nutrients or non-soil issues. This comparison is particularly important for secondary and micronutrients that may also reduce plant uptake of other nutrients such as nitrogen, which could otherwise misidentify the deficiency and lead to the wrong corrective treatment (a common problem when only one plant sample is collected). Plant and soil samples should be collected within 7-10 days of symptom development to identify the nutrient deficiency and to have enough time for a rescue fertilizer application if possible. Plant samples collected after this window may be suspect as other issues may develop and confound the results.

The picture below shows patchy yellowing in a spring wheat field during tillering stage. Plant and soil samples (good and bad) determined that sulfur was deficient in yellow areas, and the grower still had options for applying sulfur fertilizer to correct the deficiency. This is a great example of paired plant and soil analysis helping the farmer choose the right corrective action, rather than blindly putting more nitrogen on yellow wheat.

Yellow wheat showing potential sulfur deficiency (upper leaves yellowing first), but there might be soil nitrogen losses too. A paired plant and soil sample is the best way to decide the right corrective action.

Collecting plant and soil samples for troubleshooting nutrient deficiencies:

  1. Collect one plant sample in the area with possible nutrient deficiency symptoms (bad) and one plant sample in an adjacent area (~50 feet) into the crop that looks normal (good).  Collect the correct plant part for that plant growth stage (see instructions on plant sample bag or plant sampling guide).
  2. Collect one soil sample (0-6 inch) from each location where you collected the “good” and “bad” plant samples.
  3. Take photographs of individual plants that show distinct leaf symptoms (not landscape photographs) from each location where you collected the “good” and “bad” plant samples. Keep these photographs for your records; these will help in interpretation of plant analysis results.
  4. Submit plant and soil samples for Complete Nutrient Analysis (also called Option F for soil samples).

If you have fields with areas of poor plant growth, now is the time to collect plant and soil samples to determine if a nutrient deficiency is the issue. The troubleshooting procedure outlined above will help you detect nutrient deficiencies early and decide upon the proper corrective action if needed. To learn more about proper plant and soil sample collection and interpreting reports, please see the resources below.

Plant Analysis Guides
Plant Sampling Guide
Interpreting Plant Analysis Reports 

Soil Analysis Guides
Soil Sampling Guide
Interpreting Soil Test Reports

John Breker

Protecting Spring-Applied Nitrogen Fertilizer from Ammonia Volatilization

in , /by

As the spring planting season gets underway, agronomists and farmers are asking about the best ways to protect spring-applied nitrogen. How much nitrogen might I lose if I cannot incorporate it? Does vertical tillage incorporate fertilizer enough? We have compiled some resources to help answer those questions.

There are three ways to lose nitrogen fertilizer: ammonia volatilization, denitrification, and nitrate leaching. In excessively wet soils, nitrogen can be lost through nitrate leaching and denitrification. However, for spring-applied nitrogen, ammonia volatilization is the main concern with dry soil conditions and unpredictable precipitation forecasts.

When you apply ammoniacal fertilizers (e.g. anhydrous ammonia, urea, UAN, ammonium sulfate) to the soil surface without sufficient incorporation, some amount of free ammonia (NH3) can escape to the atmosphere. Sufficient incorporation with tillage or precipitation is needed to safely protect that nitrogen investment below the soil surface.

Ammonia volatilization risk depends on soil and environmental factors (Table 1) and the nitrogen fertilizer source (Table 2). Typically, we are most concerned about ammonia volatilization for surface-applied urea or UAN. It is not easy to estimate how much nitrogen might be lost, and sometimes the losses can be substantial. Although you cannot change the soil type or weather forecast, you do have control over the nitrogen source and application method (Table 2) to protect your nitrogen investment.

Table 1. Relative risk factors for ammonia volatilization
Factor High risk Low risk
Soil pH >7 <6
Soil moisture Moist Dry
Soil temperature >70 °F <50 °F
Rainfall, irrigation Little or none, heavy dew >0.3 inch after N application
CEC (cmol/kg) <10 >25
Soil surface residue >50% residue cover (no-till, pasture, turf) Bare
Application method Surface broadcast Incorporated, subsurface band
Havlin, J.L., S.L. Tisdale, W.L. Nelson, and J.D. Beaton. 2014. Soil fertility and fertilizers: An introduction to nutrient management. 8th ed. Pearson, Upper Saddle River, NJ.
Table 2. Estimated ammonia volatilization for different nitrogen sources, application methods, and rainfall scenarios on soil with pH > 7 (high risk).
Fertilizer source Application method Precipitation after fertilizer application
> 0.5 inch rain within 2 days Little or no rain likely within 7 days
% fertilizer nitrogen lost
Urea or UAN Broadcast 0-20 2-40
Dribble 0-15 2-30
Incorporated 0-10 0-10
Ammonium sulfate (AMS) Broadcast 0-40 5-60
Incorporated 0-10 0-30
Ammonium nitrate Broadcast 0-20 5-30
Incorporated 0-10 0-20
Anhydrous ammonia Injected 0-2 0-5
Messinger, J.J. and G.W. Randall. 1991. Estimating nitrogen budgets for soil-crop systems. In: Follett, R.F., D.R. Keeney, and R.M. Cruse, editors, Managing nitrogen for groundwater quality and farm profitability. SSSA, Madison, WI. pp. 82-214.

Practices to reduce ammonia volatilization for urea or UAN, in order of most effective practice

  • Apply urea in subsurface bands at least 3 inches below the soil surface. A shallow urea band (1 or 2 inches deep) acts like a slow-release anhydrous ammonia band, and nobody should ever apply anhydrous ammonia that shallow.
  • If nitrogen will be broadcast with incorporation, make sure the fertilizer is sufficiently incorporated at least 2 inches below the soil surface to ensure good soil coverage. A chisel plow or field cultivator are good incorporation tools. The popularity of high-speed disks (vertical tillage) has led some people to think that it counts as a meaningful incorporation event. In reality, it just moves soil and crop residue around on the soil surface without really incorporating the fertilizer. Take a look after you run across the field and you will see white urea granules remaining on the soil surface. Do you remember the old soil-applied herbicide incorporation videos from the 1970s? Those classic videos provide great examples of what a thorough incorporation job really requires. NDSU Extension has posted them online: https://vimeo.com/216680310/e843149fdd
  • If nitrogen will be broadcast without incorporation, try to time the fertilizer application right before rain (at least 0.5 inches of precipitation). Soils with good crop residue cover (no-till) may require more rain to sufficiently move urea or UAN into the soil.
  • If no rain is forecasted in the near future, consider applying a urease inhibitor on urea or UAN to provide temporary protection until rain arrives. The active ingredient NBPT has been widely researched and shown to reduce nitrogen losses; make sure the active ingredient rate is 1.3 to 1.8 lb NBPT per ton of urea to ensure effective NBPT activity and protection. NBPT begins to break down after 7 to 14 days. In addition, it is important to remember that nitrification inhibitors like nitrapyrin and DCD do not protect against ammonia volatilization.

These practices should also be considered if you will be applying in-season nitrogen fertilizer later in the summer. It is always best to apply nitrogen below the soil surface, such as injected anhydrous ammonia or coulter-injected UAN, to protect nitrogen fertilizer. For surface-applied urea or UAN, you should time the fertilizer application just before a rainfall or consider NBPT to extend the rainfall window.

The higher ammonia loss potential for ammonium sulfate (Table 2) often surprises people (and we get questions about it). On calcareous soils with high pH, the initial reaction products of ammonium sulfate [(NH4)2SO4] and calcium carbonate (CaCO3) can produce free ammonia, which may be lost if ammonium sulfate is lying on the soil surface. This is a similar reaction process to free ammonia formation with diammonium phosphate (DAP, 18-46-0) applied to calcareous soils. This is why AMS and DAP are not suggested as seed-placed fertilizers on calcareous soils because of the ammonia toxicity risk to seedlings. Please note that urease inhibitors like NBPT will not protect ammonium sulfate from ammonia volatilization.

Helpful resources

Nitrogen extenders and additives for field crops (NDSU) https://www.ag.ndsu.edu/publications/crops/nitrogen-extenders-and-additives-for-field-crops

Should you add inhibitors to your sidedress nitrogen application? (Univ. Minnesota) https://blog-crop-news.extension.umn.edu/2020/06/should-you-add-inhibitors-to-your.html

Split the risk with in-season nitrogen (AGVISE Laboratories) https://www.agvise.com/split-the-risk-with-in-season-nitrogen/

John Breker

Fall-applied Nitrogen Fertilizer: A Couple Simple Rules

in , /by

This article is shared annually to help answer frequently asked questions about nitrogen fertilizer applications and nitrogen losses in the fall.

October is here, and many people are preparing for fall nitrogen fertilizer applications. Before you hit the field, we want to share these important reminders about fall nitrogen application timing and placement to help you reduce potential soil nitrogen losses through fall and winter.

It is important to wait until soil temperatures reach 50 °F (10 °C) before applying fall nitrogen to reduce the risk of soil nitrogen loss. Once nitrogen fertilizer is applied, soil microbes begin converting ammonium-nitrogen (NH4+) to nitrate-nitrogen (NO3-), a process called nitrification. In the nitrate form, nitrogen is vulnerable to loss through nitrate leaching or denitrification. Soil temperatures cooler than 50 °F help slow microbial activity and keep nitrogen in the safer ammonium-nitrogen form longer. This applies to any ammoniacal nitrogen fertilizer source, which includes anhydrous ammonia, urea, UAN, and ammonium sulfate.

Quick rules for fall-applied nitrogen timing

  1. Wait until after October 1 because cool soil temperatures are more consistent and reliable after this date. After October 1, measure soil temperature in the early morning (6 a.m. to 8 a.m.) at the 4-inch soil depth.
  2. When the 4-inch soil temperature has reached 50 °F (10 °C), it is relatively safe to start applying anhydrous ammonia.
  3. Wait one week after the anhydrous ammonia-safe date to apply banded urea.
  4. Wait two weeks after the anhydrous ammonia-safe date to apply broadcast urea.

Soil temperature map from the North Dakota Agricultural Weather Network (NDAWN) from 21 September 2025. You can find an updated daily soil temperature map at the NDAWN website.

It is a good idea to keep a soil thermometer with you to measure the current soil temperature in the field. In addition to NDAWN, a number of regional climate mesonets have online tools to search for local and regional soil temperatures.

The 50 °F soil temperature rule of thumb is particularly important for soils prone to nitrogen loss: well-drained, coarse-textured soils are prone to nitrate leaching and poorly-drained, fine-textured soils are prone to denitrification. If such soils receive excess precipitation or become saturated (waterlogged) through fall or spring, soil nitrate can be lost through leaching or denitrification. In general, it might be better to apply nitrogen fertilizer on such soils in spring. But, if you must apply nitrogen fertilizer in the fall, make sure you wait until soil temperatures are cold enough to keep it in the ammonium-nitrogen form for a longer period of time to reduce potential soil nitrogen losses.

For fall-applied nitrogen, subsurface banding or incorporation is also important to reduce ammonia volatilization, another potential nitrogen loss mechanism. Fall precipitation (rain or snow) is often too sporadic and unreliable to be considered an effective incorporation “strategy” for broadcast applications. Fall-applied urea should be banded below the soil surface (3 inches or deeper) or incorporated with tillage (at least 3-4 inches) to ensure complete coverage.

Shallow fertilizer bands or shallow incorporation with vertical tillage does not provide adequate soil coverage to prevent ammonia volatilization. If soils are very dry, successful incorporation may not be possible because tillage can produce large, uneven clods that leave nitrogen fertilizer exposed to the atmosphere and vulnerable to ammonia volatilization. Although dry soil poses a lower risk of ammonia volatilization than moist soil, soil moisture is not the only factor that contributes to ammonia volatilization risk (Table 1).

Fall-applied anhydrous ammonia should be banded 5 to 6 inches deep. Ensure that anhydrous ammonia trenches are sealing properly to prevent gaseous ammonia losses from the trench. In addition, the nitrification inhibitor nitrapyrin (brand name N-Serve) can be added to anhydrous ammonia to slow nitrification, offering additional insurance to keep nitrogen in the safer ammonium-nitrogen form for longer. Nitrapyrin is also available in formulations for dry and liquid nitrogen products. Please note that nitrapyrin degrades faster and loses its effectiveness at warmer soil temperatures, so it is no substitute for cooler soil temperatures (<50 °F).

Fall-applied nitrogen is a convenient way to allocate time and labor resources, leaving one less thing to do in the spring. But, you must be smart and consider fertilizer source, timing, and placement options to make sure that the nitrogen applied in the fall will still be there next spring. With fertilizer prices still remaining high, now is not the time to risk soil and fertilizer nitrogen loss.

John Breker

Soil Nitrogen Trends – Fall 2023: Some Up, Some Down

in , , , /by

The 2023 drought was an all-too-soon reminder of the widespread 2021 drought. It covered much of the upper Midwest, 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 higher than normal. Yet, some regions were spared the drought and received above-average rainfall, and achieved record-setting crop yields. For these regions, the amount of residual soil nitrate-N after high-yielding crops was near or below average. 

The 2023 AGVISE soil test summary data highlights the great variability following the drought. The median amount of soil nitrate-nitrogen across the region was higher than the long-term average following wheat. Over 28% of wheat fields had more than 60 lb/acre nitrate-N (0-24 inch) remaining. Yet, another 17% of wheat fields had less than 20 lb/acre nitrate-N remaining, suggesting either lost crop yield or protein due to insufficient nitrogen nutrition. For any given farm, the great variability in residual soil nitrate-N across all acres makes choosing one single nitrogen fertilizer rate impossible for next year, and soil testing is the only way to decide that right rate for each field.

Through zone soil sampling, we are also able to identify that residual soil nitrate-nitrogen can vary considerably within the same field. This makes sense because we know that some areas of the field produced a fair or good 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-nitrogen 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 determine 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. 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 and Canadian Prairies. Each year, AGVISE summarizes soil test data for soil nutrients and properties in our major trade regions of the United States and Canada. For more soil test summary data and other crops, please view our soil test summaries online: https://www.agvise.com/resources/soil-test-summaries/

Jodi Boe

Two Graphics You Should Know Before the 2023 Growing Season

in , , /by

This article originally appeared in the AGVISE Laboratories Spring 2023 Newsletter

The goal of AGVISE Newsletters is to inform you and your customers of important soil fertility information relevant to our area. Often, visuals or graphs are much more powerful at communicating a message than words. With that in mind, I want to share two figures I think you should know about going into the 2023 growing season with a short synopsis and where you can find more information on the topic.

Adapted from the “Biostimulants” episode of the University of Minnesota Extension Nutrient Management Podcast https://nutrientmanagement.transistor.fm/episodes/biostimulants-52305fc9-6c01-4907-8507-2bcf4c708a08

Right now, there are many biological products and fertilizer additives on the market. In particular, asymbiotic nitrogen-fixing products have gained a lot of attention, but many have little or no university research evaluating them. Any grower wanting to try new products should test them on a small acreage first, before adopting them across the whole farm. To the left is a diagram of how such an on-farm trial would look. The key factors of a meaningful on-farm trial include a control treatment (the standard practice), the standard practice plus the product, and randomized replication (at least three replicates, randomized so that one treatment is not always on the east or west side of the trial area).

If the standard nitrogen rate will be reduced when the product is used, a treatment should also be included that compares the same reduced nitrogen rate without the product (this three-treatment setup is what is pictured). If the standard nitrogen rate is higher than the crop N requirement, maybe if you do not have a current soil nitrate-N test or just general overapplication, a reduced nitrogen rate plus the product that produces the same crop yield as the standard practice does not mean that the product is producing additional nitrogen for the crop; it may just mean that the grower can cut back their standard nitrogen rate.

Slide from Dr. John Jones’ 2023 AGVISE Seminar presentation, Phosphorus and Potassium: A Fresh Look with Fresh Data https://www.agvise.com/resources/seminars-and-events/

With fertilizer prices remaining high, it is tempting to cut back phosphorus and potassium inputs to save money. As tempting as this is, do not cut back farther than the fertilizer rates needed to meet the critical soil test level, as optimum soil-test P and K levels are required to achieve the highest response from nitrogen fertilizer. While working to update the Wisconsin phosphorus and potassium fertilizer guidelines, Dr. John Jones at the University of Wisconsin has put together some excellent data illustrating the reality of Liebig’s Law of the Minimum: when P and K fertility needs are unmet, the return from nitrogen fertilizer investment will be reduced compared to when P and K are at optimum levels. This means pouring on more nitrogen will not increase crop yield unless you are doing a good job of managing P and K too. Although not shown here, Dr. Jones also has data showing that corn and soybean yield response to P is reduced when K fertility needs are unmet.

John Breker

Early Soil Nitrate Trends after Wheat in 2022

in , , /by

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.

 

John Breker

Prevented Planting Acres? What to do for 2023

in , /by

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.

John Breker

Soil Sampling for Nitrogen in a Delayed Spring

in , , /by

Spring planting is clipping along in some parts of the region, while other parts are still waiting to hit the field, as excessive rainfall and cold temperatures have delayed spring field work and planting. Who would have thought last fall that this is what spring 2022 would look like, after the worst region-wide drought in 30 years? Mother Nature always reminds us to stay prepared for anything.

A delayed spring start means that every day in the field is important. AGVISE delivers next-day turnaround on processing soil samples. The soil samples are analyzed and reported the next business day after arrival at the laboratory. Soil test results are posted to our online AGVISOR portal for quick and easy access. If you need any soil sampling supplies for spring, please let us know and we will send them to you right away.

So, what is the best strategy for spring soil testing and assessing soil nitrogen losses after the rain? The compressed fertilizer and planting window might not leave enough time to adjust preplant fertilizer rates, especially if the field is just barely dry enough to plant. If soil nitrogen losses have occurred following spring rains, a spring soil test collected now will be helpful to create a split-applied nitrogen plan or to direct a supplemental nitrogen application later. In the AGVISE Spring 2022 Newsletter, we answered some questions on split-applied nitrogen application strategies, so please take a look at those options for applying nitrogen during the growing season.

Short-season crops develop quickly, so additional nitrogen should be applied in the upcoming weeks. A soil sample collected before or shortly after planting will provide the best assessment of preplant soil nitrogen supply and losses. Do not wait too long to collect the soil sample because, as we move into June, plant nitrogen uptake and nitrogen mineralization from soil organic matter will make the soil nitrogen result more difficult to decipher. To maximize yield in small grains, apply all topdress nitrogen before jointing (5-leaf stage). Any nitrogen applied after jointing will mostly go to grain protein. In canola, apply nitrogen during the rosette stage, before the 6-leaf stage.

Long-season crops like corn offer more flexibility and time for in-season soil sampling and nitrogen application. Rapid nitrogen uptake in corn does not begin until after the V6 growth stage. The Pre-sidedress Soil Nitrate Test (PSNT) can help you decide the appropriate sidedress nitrogen rate. For more details, take a look at the PSNT article link for instructions on collecting and submitting PSNT soil samples. The PSNT requires a 0-12 inch depth soil sample taken when corn plants are 6 to 12 inches tall (at the whorl), usually in late May or early June. Late-planted corn may not reach that height before mid-June, but PSNT soil samples should still be collected during the first two weeks of June. If spring rainfall was above normal, Iowa State University guidelines provide additional PSNT interpretation criteria for excessive rainfall, manured soils, and corn after alfalfa.

If you have any questions on the best strategies for spring soil sampling and in-season nitrogen application options, please call our technical support team and we will be happy to answer any questions you may have.

Jodi Boe

Zone Soil Sampling and Variable Rate Fertilization: Optimizing profits

in , , /by

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.

John Lee

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

in , , , , /by

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.