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.

 

 

Fall-applied Nitrogen Fertilizer: A Couple Simple Rules

The beginning to mid-October is when soil temperatures across the northern Great Plains and Canadian Prairies typically drop below 50 °F (10 °C). This is the soil temperature threshold that we wait to reach before applying fall-applied nitrogen fertilizer. It is important to wait until soil temperatures are cold enough (<50 °F) to help 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. The colder soil temperatures slow microbial activity, thus keeping more nitrogen in the safer ammonium-nitrogen form. This applies to any ammoniacal nitrogen fertilizer source, which includes anhydrous ammonia, urea, and ammonium sulfate.

Map courtesy of the North Dakota Agricultural Weather Network (NDAWN).
You can find an updated average bare soil temperature map here

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 prevent ammonia volatilization, another potential nitrogen loss mechanism. Fall precipitation (rain or snow) is too sporadic and unreliable to be considered an effective incorporation “strategy” for fall-applied nitrogen. 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 enough soil coverage to prevent ammonia volatilization.

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 delay nitrification, offering additional insurance to keep nitrogen in the safer ammonium-nitrogen form for longer. However, please note that its efficacy decreases with warmer soil temperatures, so it is no replacement for cool soil temperatures (<50 °F).

In conclusion, fall-applied nitrogen is a great 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 fall will still be there next spring.

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).

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.

Update: Feed Nitrate Testing in a Drought Year

Drought continues to stress crops across the upper Midwest and the Canadian Prairies. As crop conditions continue to deteriorate in some places, we have received more phone calls about salvaging the drought-stressed crop as livestock feed and the need for feed nitrate testing. As you consider what to do with your standing crop, whether to harvest for grain or cut for hay, an important part of that consideration will be the nitrate concentration of the crop.

When drought-stressed annual crops (e.g., wheat, barley, oat, corn) are cut or grazed, producers must exercise caution about livestock nitrate poisoning when feeding these forages. Drought-stressed crops often accumulate nitrate because plant uptake of nitrate exceeds plant growth and nitrogen utilization. Nitrate is usually concentrated in lower plant parts (lower stem or stalk). When livestock, particularly sheep and cattle, ingest forages with a high nitrate concentration, nitrate poisoning can occur.

Instructions for collecting and submitting a feed nitrate test

1. Collect the plant part that livestock will consume, which may be the whole aboveground plant. If grazing, be mindful of the grazing height because the plant nitrate concentration will be lower near the base of the plant. If baling for hay or chopping for silage, cut at the intended cutter bar height.

Picture used for feed nitrate email - corn collage

2. Cut plant material with sturdy garden shears into 1- to 2-inch pieces. Mix the chopped plant parts together and take one quart-sized subsample for analysis (about four good handfuls).

3. Place subsample in AGVISE Plant Sample Bag. Write “Feed Nitrate” as the crop choice and select “Nitrate-nitrogen” as the analysis option.

    • If you are considering chopping corn for silage, also write “%Moisture” as an additional analysis because you will need to know if the moisture content is still adequate for silage fermentation. You may be surprised how much water will still be in drought-stressed corn stalks.

4. Ship plant sample to AGVISE Laboratories. If you cannot ship the sample right away, store it in a refrigerator until you can ship it.

IMPORTANT: Resample the hay or silage before feeding to any livestock. You need to know what is actually being fed to livestock, and you may need to blend it with other feed sources to dilute the nitrate concentration. For dry hay in bales, the nitrate concentration will not change in storage; use a hay probe to obtain the best possible feed sample. For silage, the nitrate concentration may decrease 20 to 50% during fermentation, so a fresh sample is necessary before feeding.

IMPORTANT: Many crop protection products have grazing restrictions on their labels that dictate if or when a crop treated with a product can be fed to livestock. Before using or selling a crop for livestock feed, check all labels of crop protection products that have been used on the crop this season. This includes seed treatments, herbicide applications, fungicide applications, and insecticide applications.

AGVISE Laboratories offers next-day turnaround for feed nitrate analysis. Rapid turnaround on nitrate analysis is important for producers debating to cut and bale or graze small grains or corn as livestock feed.  We also provide livestock water analysis, which includes total dissolved solids, nitrate, and sulfate, to assess livestock drinking water quality. Please call AGVISE staff in Northwood, ND (701-587- 6010) or Benson, MN (320-843-4109) with questions about nitrate, feed and hay quality, or water analysis. We can send you sampling supplies if needed.

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Helpful resources on using drought-stressed crops for livestock feed:

Nitrate Poisoning of Livestock (NDSU)

Using Drought-Stressed Corn as Forage (SDSU)

Drought-Related Issues in Forage, Silage and Baleage (Univ. of Missouri)

Feed Nitrate Testing in a Drought Year

Drought is an unwelcome but well-known phenomenon on the Northern Plains and Canadian Prairies. Rainfall has been sparse and scattered across the region, and high temperatures exceeding 90 to 100° F (32 to 38° C) have already caused stress to young crops. These same stresses have also wracked pastures, prompting livestock producers to think about alternative feed options for cattle. Believe it or not, we have already received questions from farmers and ranchers about decisions to cut and bale or graze small grain fields for livestock feed.

When drought-stressed annual crops (e.g., wheat, barley, oat, corn) are cut or grazed, producers must exercise caution about livestock nitrate poisoning when feeding these forages. Drought-stressed crops often accumulate nitrate because plant uptake of nitrate exceeds plant growth and nitrogen utilization. Nitrate is usually concentrated in lower plant parts (lower stem or stalk). When livestock, particularly sheep and cattle, ingest forages with a high nitrate content, nitrate poisoning can occur if large amounts of nitrate convert to nitrite in their digestive system.

Dry soil conditions and high soil nitrate levels favor plant accumulation of nitrate. There is one upside to very dry soil conditions: Some soils may not have had enough soil water to convert all nitrogen fertilizer from the ammonium form to the nitrate form, especially if nitrogen fertilizer was applied in a concentrated band that delays nitrification. Therefore, this may limit the amount of soil nitrate available for plant uptake and accumulation. Regardless, there is still variation across the landscape, and a feed nitrate analysis is the best method to assess livestock nitrate poisoning risk.

When collecting plant material for nitrate analysis, collect the plant parts that the livestock will eat. If plant material will be grazed, recall that lower plant parts contain higher nitrate concentrations; monitor grazing height closely. If plant material will be cut and baled, you should collect plant material above the cutter bar height. Alternatively, plant material can be sampled with a hay probe after being baled.

For the fastest turnaround, submit feed materials for nitrate analysis using a plant sample bag. Write “feed nitrate” for crop choice and select “nitrate-nitrogen” as the analysis option. 

AGVISE Laboratories offers next-day turnaround for feed nitrate analysis. Rapid turnaround on nitrate analysis is important for producers debating to cut and bale or graze small grains or corn as livestock feed.  We also provide livestock water analysis, which includes total dissolved solids, nitrate, and sulfate, to assess livestock drinking water quality. Please call AGVISE staff in Northwood, ND (701-587- 6010) or Benson, MN (320-843-4109) with questions about nitrate, feed/hay quality, or water analysis. We can send you sampling supplies if needed.

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