John Breker

AGVISE Demonstration Project: Lowering Soil pH with Elemental Sulfur

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This article originally appeared in the AGVISE Laboratories Spring 2025 Newsletter.

There may not be silly questions, but there are silly answers. Every so often, we get questions about unusual solutions to manage calcareous soils in the northern Great Plains and Canadian Prairies. The most frequent oddball “solutions” involve lowering soil pH with elemental sulfur on calcareous soils. Such suggestions might work on acidic soils; however, the dominant calcareous soils in the region have high pH (>7.3) and tons of natural calcium carbonate that make such attempts impractical and expensive. To put the nail in the coffin, AGVISE Laboratories started some long-term demonstration projects to show plainly why such ideas do not work or may cost way too much!

If possible, we’d like an easy and cheap solution to lower soil pH, like applying only 100 to 200 lb/acre elemental sulfur (S). In soil, elemental S oxidizes to sulfuric acid, which can lower soil pH. However, the large amount of calcium carbonate (free lime) keeps our soils buffered at high pH. To lower soil pH permanently, you must first react and neutralize the carbonate with elemental S before the soil pH can budge. With 100 lb/acre elemental S applied each year, that does not sound too difficult, right?

Elemental sulfur project with rates ranging from 0 to 40,000 lb/acre elemental sulfur. Can you identify the 20 ton/acre rate?

Not so fast. A soil with only 1% calcium carbonate equivalent (CCE) takes 3.2 ton/acre elemental S (6,400 lb/acre) to neutralize the carbonate alone in the 0-6 inch soil depth. In 2020, we started an elemental S project at Northwood, ND on soil containing 4.5% CCE, which would require literal tons of elemental S to lower soil pH. A previous project started in 2005 had used 10,000 lb/acre elemental S, but it was not enough to lower soil pH beyond pH 7.8 after 15 years. This time, we decided to get serious and use elemental S rates from 0 to 40,000 lb/acre (Figure 1). The elemental S rates were intended to hit above and below the target 30,000 lb/acre elemental S rate required to react and neutralize 4.5% CCE.

For the first three years of the project, we saw little to no change in soil pH, regardless of elemental S rate. The oxidation process that converts elemental S to sulfuric acid is a slow, biological process that can take a long time. In Fall 2024, we finally saw real changes in soil pH following elemental S application. The 16,000 lb/acre elemental sulfur rate reached pH 7.5. The 24,000 lb/acre elemental sulfur rate reached pH 7.0. The 40,000 lb/acre elemental sulfur rate reached pH 6.0, a dramatic change! The lowest 8,000 lb/acre elemental sulfur rate, however, was no different than the control.

There is still some unoxidized elemental sulfur and unreacted calcium carbonate in the soil, and we will continue to monitor these long-term demonstration plots in future years. The project demonstrates that elemental sulfur can lower soil pH, but it also shows that the very high amounts of elemental sulfur required are both impractical and expensive. A few hundred pounds of elemental sulfur applied each year will get you nowhere. In contrast, the very high elemental sulfur rates will break the bank. This is why we consider such “solutions” as either ineffective attempts or downright silly wastes.

Brent Jaenisch

Soybean Cyst Nematode (SCN) Egg Numbers Continue to Increase

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This article originally appeared in the AGVISE Laboratories Spring 2024 Newsletter.

Over the winter months, we received a lot of questions about the increasing soybean cyst nematode (SCN) egg count trends across the region. Soybean cyst nematode is the most damaging soybean pest in the United States, and the problem is becoming worse. The AGVISE SCN summary over the past five years (2019-2013) shows that SCN egg counts are increasing steadily in Minnesota and North Dakota,
which is a serious concern for SCN management into the future.

State Year SCN Egg Count (eggs per 100 cm3 soil, % of soil samples)
0 1 – 200 201 – 2,000 2,001 – 10,000 >10,000
Minnesota 2019 17% 16% 36% 27% 3%
2020 15% 10% 28% 38% 8%
2021 10% 9% 27% 40% 14%
2022 11% 8% 27% 40% 15%
2023 8% 7% 21% 45% 20%
North Dakota 2019 43% 15% 25% 14% 4%
2020 42% 14% 25% 17% 2%
2021 30% 15% 23% 23% 9%
2022 29% 15% 25% 24% 8%
2023 20% 12% 21% 36% 12%

In Minnesota, 65% of SCN soil samples in 2023 had more than 2,000 eggs per 100 cm3 soil. This is the threshold where an SCN-resistant soybean variety is suggested, yet some soybean yield loss is still expected. The percentage of soil samples with zero or low egg counts (<200 eggs) has declined from 17% in 2019 to 8% in 2023, meaning that there are fewer SCN-free fields in the state. More alarming,
the percentage of soil samples with more than 10,000 eggs has skyrocketed from 3% in 2019 to 20% in 2023. This is the threshold above which planting soybean is not suggested, whether resistant or tolerant to SCN, and a non-host rotation crop is suggested.

In North Dakota, 48% of SCN soil samples in 2023 had more than 2,000 eggs per 100 cm3 soil. The percentage of soil samples with zero or low egg counts (<200 eggs) has declined from 43% in 2019 to 20% in 2023. More alarming, the percentage of soil samples with more than 10,000 eggs has quickly increased from 4% in 2019 to 12% in 2023.

These SCN summary trends highlight a growing concern for soybean growers. With SCN, an ounce of prevention is worth more than a pound of cure. A consistent SCN soil sampling program remains one of the best tools to monitor SCN populations. This is how we learn if current SCN management strategies like crop rotation and SCN-resistant varieties are working, or if you need to reevaluate your soybean
management plan. A detailed guide to collecting SCN soil samples can be found at the SCN Coalition website.

John Breker

Zone Soil Sampling: How Many Zones?

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Zone soil sampling has become a standard practice in precision nutrient management, but the grand question remains – How many zones should you be soil sampling?

Well, it depends! It just makes sense that a field with more variability requires more zones than a field with little variability. Zone soil sampling separates parts of fields that behave differently into similar zones that can be managed together. Common data layers used to build zone soil sampling maps include satellite imagery, plant vegetation indices, crop yield, salinity, topography, and even bare soil color.

As a soil testing laboratory, AGVISE does not know what data layers are used to create the zone maps, but we do know the soil nutrient levels in each zone. Clients often ask how many zone soil samples should be collected in each field to get the best soil nutrient information. Common sense tells us that splitting fields into more zones should provide more detailed soil nutrient data.

With soil test data from thousands of zone soil sampled fields, we mined the AGVISE database to see what the average range in soil test levels per field (high testing zone minus low testing zone) could tell us about field variability and the number of zones that should be sampled. The table summarizes the average range in soil test levels for over 24,000 zone soil sampled fields in 2023. The number of zones ranges from 3 to 8 zones per field. You can see, as the number of zones increases, the difference between the high zone and low zone gets larger and larger.

This data reminds us that more zones per field can tell us more about the soil nutrient status in each field, providing more powerful information to develop variable-rate fertilizer applications. If you have variable landscapes with rolling topography, diverse soil types, or salinity problems, you may have to take more zone soil samples per field (5-7 zones) to see the greatest differences in soil fertility and to take full advantage of variable-rate fertilizer applications. If your landscapes have less variability with fewer soil types, relatively flat topography, and no salinity problems, then you can probably take fewer zone samples per field (3-4 zones).

Jodi Boe

Lime Works: The Results Are In

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This article was originally published in the AGVISE Laboratories Winter 2023 Newsletter.

In the fall of 2022, I hired a custom applicator to haul and spread lime across 238 acres of my family’s farm in western North Dakota. The reason? To increase soil pH on five fields with very low soil pH. One field even had a soil pH of 4.7, so these were good candidate fields for a practical case study for liming on a real farm operation.

I wrote more about the soil sampling process and lime application in the AGVISE Winter 2022 newsletter (https://www.agvise.com/wp-content/uploads/2022/11/AGVISE-Newsletter-2022-Winter.pdf). Each field received approximately 2 ton/acre sugar beet lime (1.4 ton ENP/acre) from Sidney Sugar in Sidney, MT, and the lime was disced to 3 inches for incorporation. After one year, the soil pH had already increased by 0.36 pH-units in the 0-6 inch soil depth. The 2023 growing season was relatively wet in southwest North Dakota, and the additional soil water certainly helped the lime react and neutralize soil acidity quickly. The incorporation with a disc also helped distribute the lime more evenly and deeply, allowing the lime to react faster. One negative side effect of tillage was a flush of annual weeds, particularly green and yellow foxtail. This was the first tillage event on these fields in 12 years, so I expect the annual weed community to diminish as we return to no-till after the one-time tillage pass.

Figure 1. Zone soil pH map of a field receiving 2 ton/acre sugar beet lime in fall 2022. Each zone increased roughly 0.36 pH-units from 2022 to 2023. (Maps created in ADMS 32, GK Technology, Inc.)

Lime also works without incorporation, just at a slower pace. In 2021, we established a no-till lime trial to investigate lime rates without incorporation. Lime was applied in May 2021, and the fall 2023 soil pH results are shown in Figure 2. The highest lime rate at 2.5 ton ENP/acre increased soil pH in the upper 0-3 inch soil depth by 0.71 pH-units over 2.5 years. So far, no effect on soil pH in the lower 3-6 inch soil depth has been observed. In most no-till systems, the most acidic part of the soil profile is located at the soil surface, and a lime application correcting soil pH in the upper 0-3 inch soil depth is still effective. This is where seedlings and roots are most vulnerable to soil acidity, so correcting soil pH at the soil surface is critical and can be accomplished with a surface application of lime in no-till systems.

Surface Soil pH (0-3 inch) in No-till Lime Trial, October 2023

Figure 2. Soil pH following surface application of lime after 2.5 years in a no-till cropping system in southwestern North Dakota.

John Breker

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

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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/

John Breker

John Breker Appointed to NAPT Oversight Committee

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This article originally appeared in the AGVISE Laboratories Spring 2023 Newsletter

John Breker was appointed to the North American Proficiency Testing Program Oversight Committee as the North Central Region representative, starting in January 2023. The North American Proficiency Testing (NAPT) Program assists soil, plant, and water laboratories with quality control and quality assurance through inter-laboratory sample exchanges as well as statistical evaluation of the analytical data. These tools help laboratories generate accurate and precise analyses, as well as provide confidence to clients that their data meets high standards.

The NAPT program guidelines have been developed for the agricultural laboratory industry by groups involved with standardizing soil and plant analysis methods in the United States and Canada. The program is authorized through the Soil Science Society of America (SSSA) and administered by the NAPT Oversight Committee, composed of representatives from regional soil and plant analysis workgroups, state/provincial departments of agriculture, and private and public soil and plant analysis laboratories.

AGVISE Laboratories has been a member of the NAPT program since its inception. AGVISE Laboratories in Benson, MN and Northwood, ND participate in the soil, plant, and water programs through NAPT, as well as the Performance Assessment Program (PAP) required for participation in USDA-NRCS programs. AGVISE is a strong supporter of NAPT and the ongoing objectives of the NAPT program.

NAPT Program Objectives

  • Provide an external quality assurance program for agricultural laboratories
  • Develop a framework for long-term improvement of quality assurance for the agricultural laboratory industry
  • Identify the variability of specific methods

 

 

John Breker

Early Soil Nitrate Trends after Wheat in 2022

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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 Lee

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

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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.

 

 

Brent Jaenisch

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

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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.

 

 

Jodi Boe

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

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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.