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Tips to Avoid Delays in Your Soil Results

With harvest closely approaching for much of the region, the dry conditions can help the harvest to progress quickly and efficiently. When harvest is efficient, fall soil sampling is efficient, resulting in sample volumes that can challenge our laboratory’s daily maximum capacity. While our goal is to keep a consistent turn-time for all samples, it is not always possible if challenges arise in the process. Following these tips can help reduce delays in the delivery of your results.  

1. Use good quality new or lightly used, heavy duty boxes for shipping samples. The #1 cause of samples being lost is damaged boxes in shipping. Reusing Amazon boxes is discouraged because the cardboard is often too thin to withstand the weight of soil samples.
2. Packing tape is cheaper than resampling. Be sure to use plenty of good quality packing tape. Make sure to use multiple strips of tape on all box seams including the vertical seam that joins the box together. This is the most damaged part on a box causing loss of samples. If you are reusing boxes, be sure to reinforce all previously taped seams and joints.
3. Full boxes with organized rows of samples hold up best during shipping. Loosely packed boxes stand the greatest chance of being crushed during shipping. Loosely packed samples also stand the greatest risk of losing sticker labels or having handwritten information worn off. Samples that are organized improve the efficiency of the lab process.
4. If possible, pack entire fields in the same box. If this is not possible, please indicate on the outside of the boxes by numbering or labeling with the actual field name. It is fine to have multiple fields in one box but try to avoid spreading multiple fields across multiple boxes. Doing this prevents delaying sample results for multiple fields if one box is lost or delayed in shipping.
5. Include completed submittal forms that indicate your account number, grower, farm, field, all sample ID’s, and the desired analysis package. Your samples can be processed more efficiently if the submittal forms are in the same box as the samples they represent.
6. If you are using soil sampling software that allows for electronic submission, be sure to have your information synced, or uploaded prior to the samples being delivered to the lab.

If you have any questions regarding shipping supplies, or sample packaging, please contact your ALGL representative.

Corn Stalk Nitrate Testing

The Corn Stalk Nitrate Test (CSNT) was developed by Iowa State University agronomists to determine if growers were using the proper amounts of nitrogen for corn production. Traditional tissue tests work well to evaluate nitrogen availability to the plant at a given point in time, the CSNT helps identify the effectiveness of the season long availability of nitrogen. This is assessed by measuring the amount of nitrate - nitrogen present in the lower portion of the corn stalk around the time the plant reaches physiological maturity.  Corn plants suffering from inadequate N availability remove N from the lower cornstalks and leaves during the grain-filling period.  Corn plants that have more N than needed to attain maximum yields, however, accumulate nitrate in their lower stalks at the end of the season.  Several factors, including weather, can have a profound effect on the results of the test.

SAMPLE GUIDELINES

Samples should be collected between 1/4 milkline to 3 weeks after black layer has formed on 80% of the kernels of most ears.  Field test areas should not be larger than 10 acres.  Collect 15 stalks and remove an 8” segment between 6” and 14” above the soil.  Place in paper bag (not plastic). Refrigerate if delay in shipping is one or more days.  Do not freeze.

INTERPRETATIONS - CSNT

The CSNT does not directly indicate how much a N application should be increased or decreased.  However, the use of this test consistently from year to year can be a valuable tool when adjusting N rates.  Since the development of this test, nitrogen prices have increased substantially, increasing the need for sound nitrogen management.  In addition, nitrogen in ground and surface waters can be a major environmental concern.  From both an environmental and an economic perspective, any tool that can help a grower manage nitrogen usage should be seriously considered.  Additional information on the corn stalk nitrate test can be found in our factsheet, “Corn Stalk Nitrate Test”, available on our website.

What Goes into Making a Nitrogen Recommendation for Corn?

Some common questions that we get asked about soil test results are, where is the nitrogen level on my report, and how do you recommend a nitrogen rate when you did not test the nitrogen level of the soil?

To begin, let’s explain why plant available nitrogen (N) is not part of our routine soil test packages. The simple answer is our climate. In the Midwest and northeastern United States, our “non-growing” seasons are when we receive much of our annual precipitation. That means that any excess applied N from a growing season probably will not carry over to the following growing season. It is likely to be lost to leaching and denitrification. So, we build our recommendations on the assumption that we are starting with little to no plant available N.

Since our recommend rate of N is not based on a soil test result, we use a projected yield goal. When harvested, a bushel of corn will remove about 0.67 pounds of N. To grow a 200-bushel corn crop we must supply a minimum of 134 pounds of N just to cover what is being removed. However, that crop is going to require more N than crop removal because we also need to grow the whole plant to grow the grain. A corn crop will take up about one pound of N in total per bushel grown, meaning that same 200-bushel crop really needs about 200 pounds of N supplied.

If you request recommendations from A&L Great Lakes for a 200-bushel crop, we will recommend 240 pounds. Most agronomists and growers will agree that this is an aggressive rate for 200-bushel corn, and it is. The reason that it is so high is that this is a starting point. We are assuming a worst-case scenario in which all the N is broadcast applied prior to planting. Unfortunately, N becomes more prone to loss the longer it stays in the soil before a crop can utilize it. A corn crop will take up about 70% of its N during the first half of the growing season and the remaining 30% will be taken up slowly all the way through physiological maturity. The likelihood of preplant application of N at a crop uptake only rate making it through the whole growing season is unlikely. The extra N supplied is to help ensure season-long availability. Fortunately, there are practices and tools that we can use to help lower the rate of N that needs to be applied.

The most common practice to lower the total amount of applied N is in-season and split applications. Whether it is sidedressing, high-clearance spreaders, or fertigation, the closer the N is applied to the time of crop uptake, the less likely it is for losses to occur. Most growers using a combination of starter N and a second application around V5 to V6, are comfortable using a rate around 1.1 pounds of N per bushel.

Another tool that can be used to reduce N application rates is the Estimated Nitrogen Release (ENR). In a good growing season, you can estimate that about 30 pounds of N will be mineralized from every 1% organic matter that is in your soil. If your soil has 3.5% organic matter, it has the potential to provide approximately 100 pounds. The problem with the natural mineralization of N is that it may not coincide with the timing that the crop needs it. So, it is not advisable to reduce the application rate by the entire 100 pounds, but 40 to 50 pounds maybe justifiable.

The Maximum Return to Nitrogen (MRTN) model is another option to use and is what the current Tri-State recommendations utilize. The idea of this model is to incorporate years of N response data from your area, N prices, and corn prices to predict the most profitable rate of N to apply.

The greatest challenge with recommending a N rate is that it is impossible to predict the weather and economy far enough into the future to know that the right decision is being made. The best way to go about making a recommendation is to use all of the tools that you have available and learn from your past practices.

Water, Salt, and Buffer pH

Increased awareness of different lab methods to measure extractable nutrients has been positive to help understand variations in soil test data from various regions of the country and why they may be different.  Like extractable nutrients there are various lab methods for testing soil pH.

Soil pH - Water vs. Salt

There is 1:1 water which uses equal parts distilled/deionized water and soil to make a slurry for pH determination. This is the common method in most of the eastern US. In drought conditions natural salts can accumulate in the soil that interfere with the pH probes used to measure the pH of the soil and water slurry. This interference can lead to a 0.2 to 0.6 drop in soil pH readings. This drop is also common in arid regions of the Western US. The severity of the drop is based on the salt levels in the soil. To overcome this issue in the arid western regions, low concentration salt water is used to stabilize the readings at 0.5 to 0.6 pH units lower than 1:1 water pH. The target pH is different for 1:1 water vs salt pH.

Buffer pH

Buffer pH is used to determine how much lime application rates. This is similar to soil pH in that it is a a buffer is added slurry of soil and water that strips all of the hydrogen from the CEC of the soil. The more hydrogen on the CEC the greater amount of reserve acidity in the soil leads to a greater decrease in the buffering solution. The greater the decrease of the buffer solutions after stripping the hydrogen from the soil indicates higher lime application rates. There are several buffer solutions that start at different pH’s and result in different buffer pH’s. Common Buffer solutions include:

• SMP
• Sikora
• Woodruff
• Adam Evans
• Mehlich

At ALGL our standard methods are 1:1 water pH and Sikora buffer pH.

Corn Silage Nitrate Testing

The inconsistent temperature and precipitation patterns throughout our region have raised concerns about the potential for nitrate toxicity in corn chopped for silage. Nitrates have the potential to accumulate in a corn plant under any stressful conditions that hinder plant growth. There are many guides, articles, and fact sheets available that discuss the interpretation of the lab data and sampling procedures for corn that has already been chopped, but there is little guidance for sampling the corn prior to harvest.

The most important step in collecting a sample from a standing corn field is that the sample must be representative of the portion of the plant that will be harvested. That means cutting it at the same height as the chopper. Nitrates accumulate primarily in the lower stalk section, so a few inch difference can have a significant impact on your results. Second, the plants that are collected need to be representative of the condition of the field. For example, if a quarter of the field is performing poorly as compared to the rest of the field, a quarter of the plants collected for the sample need to be from that section, three quarters from the good area of the field. A sample should consist of a minimum of 15 plants to best represent the average of the whole area being sampled. The sample also needs to be collected as close to harvest as possible, because nitrate levels can change quickly as the weather changes.

Prior to sending the sample to the lab, the plants need to be chopped and thoroughly mixed. This is best accomplished with a lawn chipper shredder.  Once all the plants are chopped and mixed, collect a 1-gallon zip top bag subsample to be shipped to the lab for analysis.

Please note that a Corn Stalk Nitrate Test (CSNT) and a feed nitrate test are very different in the sample collection and will give you very different results. A CSNT involves collecting only an 8-inch section of the lower stalk around black layer. This test is used to evaluate the effectiveness of a nitrogen program and does not necessarily represent a potential for nitrate toxicity.

For more information please see our A&L Great Lakes fact sheet, Nitrate Toxicity in Feed.

Another excellent resource is from the University of Wisconsin Extension, Nitrate Poisoning in Cattle, Sheep, and Goats.

For any additional questions regarding feed nitrate testing and sampling, feel free to contact your A&L Great Lakes Laboratories agronomist or call the laboratory directly as 260-483-4759. 

Tissue Testing Near the End of the Growing Season

Collecting plant tissue samples throughout the entire growing season to monitor nutrient levels has become a common practice over the last few years. As most of the crops in our region are now well into reproductive stages, plant tissue test results need to be evaluated with a cautious eye.

As plants transition from vegetative growth stages to reproductive stages, the nutrient content of the plant leaves will change, most noticeably nitrogen and potassium. These nutrients are mobile in plants, so as the plant starts transitioning to grain-fill, they may be translocated from the leaf to the grain resulting in low tissue test ratings that may not necessarily indicate a yield-reducing nutrient deficiency.

Another common trend in plant tissue nutrient levels is an increase in micronutrient concentrations as the plants approach physiological maturity. This is a result of carbohydrates and other carbon-based molecules being translocated from the leaf tissues to the grain effectively reducing the biomass of the leaf. The micronutrients (iron, manganese, zinc, and copper) are immobile in the plant tissue, so they remain in the leaf that has a lower mass and are now present at a higher concentration. The micronutrients may be rated as high or very high, however, this not necessarily an indicator of excessive fertility or potential toxicity.

While plant tissue testing can be a very effective tool for fine-tuning a fertility program, be careful not to make drastic decisions based on late-season plant tissue test results alone.

Don’t Forget the Lab as You Prepare for Fall Soil Sampling

While we are finishing family vacations, county fairs, and getting ready to send the kids back to school, it is also time to begin preparing for the fall soil sampling season. As you begin to layout your sampling strategy and processes, please keep the lab in mind.

• Contact the lab or your regional ALGL regional agronomist to update changes that need to be made to your lab account. Changes might include:
  • Email addresses to receive status notifications, PDF soil test reports, electronic data files
  • Changes in GIS software being used
  • If you are adopting Mehlich 3 data
  • Changes to from ppm and lbs/acre
  • Needed changes in report format
• Make a list of fields that are up for resampling. The annual soil sampling history reports on eDocs are helpful to help ensure you a not missing a resample field. If you are on a standard 2-year sampling cycle, look back to the 2021 report.
• Review the requirements for sampling dates on programs like H2Ohio. Some programs may have requirements that will require you to collect soil samples sooner than the normal sampling cycle.
• Contact the lab or your regional ALGL regional agronomist to order sampling supplies.
• Be sure to check the expiration date on UPS shipping labels you may have in inventory, if they are expired order new.
• If you are expecting an increase in sample numbers, contact the lab or your regional ALGL regional agronomist to discuss updates in volume discounts.

Planning makes the season go much better for everyone involved. If you find yourself rushed in season to get soil samples collected and then fertilizer recommendations complete, we encourage to you consider sampling a season in advance. For example. If the client spreads fertilizer in the fall, collect the soils sample in the spring so that the recommendations can be made outside of the soil sampling season.

Sampling for Soybean Cyst Nematode (SCN) and Other Nematodes Mid Summer

Dry weather this year has stressed the crops enough in many areas. This additional stress has made many underlying issues visible that were normally masked with good growing conditions. Elevated populations of soybeans cyst nematode (SCN) are being found in areas of stunted and yellow soybeans. Especially in light textured soils with a history of frequent soybean crops. Other species of nematodes are impacting corn.

The best time to sample for SCN is in the fall just prior to harvest to determine max population levels in whole field sampling. Diagnostic sampling for SCN focuses samples to be collected in a smaller area where the soybeans are affected during the growing season. This earlier testing may not indicate maximum seasonal population but can identify the location and relative severity of SCN infestations. Collect a minimum of eight 0-8” deep cores near the affected soybean rows to make a composite sample. It is best to collect another sample just outside the impacted area, near the soybean rows, to determine if the injury is due to an isolated population in the field.

When collecting and shipping nematode samples to the laboratory, do so quickly and avoid exposing the samples to extreme temperatures. Overnight shipping is not required. Nematode samples sent to ALGL should request the NCYST test package that will return SCN adult and cyst numbers, along with interpretations of potential percent of yield reduction. For other crops, request the N3 package which is an adult only count of a wide variety of nematodes that impact other crops. This test will also yield an interpretation of crops that maybe impacted by the species of nematodes present.

Additional Resources:

Not All Nematodes Are the Same - Corn Nematodes

Sampling for SCN

The Value of Wheat Straw

Wheat grain and fertilizer prices have been variable recently. If you are faced with the decision of whether to remove the straw or leave it in the field, take a few minutes to calculate the value of the nutrients that will be removed with the straw. Make sure you are adequately compensated for the replacement costs of these nutrients.

IPNI nutrient removal data shows wheat straw removing 12 pounds N, 3.3 pounds of P2O5, and 24 pounds of K20 per ton. An 80 bushel per acre wheat crop will produce on average 4 ton per acre of straw with a low harvest cut height. 

Be sure to calculate the cost to replace those nutrients when pricing the straw product. The cost to replace the P and K removed in the straw is approximately $50 per ton. The replacement cost of the N, P, and K is about $55 per ton. These prices will vary with the fertilizer market. Several factors can affect the actual removal rates such as rainfall following harvest and prior to bailing that will leach a portion of the potassium back to the soil.

If you would like to submit a straw sample to the lab for testing, we can help you more accurately estimate the nutrients removed and your ALGL regional agronomist can help you with the calculations if needed.

“Good’ Vs. “Bad” Tissue Test Data in a Challenging Growing Season

Tissue samples are often submitted to the lab with the sample ID ‘s of “good” and “bad”, and sometime the tissue test data results are very similar. The dry weather this year has increased the appearance of these samples. Sometimes the “bad” sample will have higher nutrient concentrations than the “good” sample.

It is advisable in tough growing conditions to take both a “good” and “bad” sample. In some cases, the samples should be labeled “bad” and “really bad”.  Even the better appearing plants may be struggling and result in low tissue test values, just not as low as the poor appearing plants.

Tissue testing lab methods are a complete acid digestion of the plant materials. The concentration is the relative amount of a given nutrient within a defined volume of plant biomass. Changing either the total amount of nutrient in the plant or changing the overall volume of plant biomass will impact the results.

The impact of nutrient uptake and plant size on tissue test results when comparing two samples.

If nutrient availability in the soil is not limiting, there is no reason to expect the tissue test data between a “good” and “bad” sample to be significantly different. If a plant is limited by physical or environmental factors leading to reduced plant growth, the biomass volume of the impacted plant will be less.  Equally decreased nutrient uptake by the impacted plant will lead to a less total nutrient in the plant tissue tested. Often the decrease in plant biomass is correlated to the relative decrease in nutrient uptake. This leads to a very similar sample nutrient concentration. If the plant biomass is severely impacted while nutrient uptake continues, the impacted plant could result in elevated nutrient levels. Notes and pictures taken at the time of sampling can be very valuable in interpreting plant tissue data.

When a nutrient deficiency is occurring, it normally only impacts one or possibly two nutrients. When all or several of the nutrients are shifted, then external forces like lack of water limiting mass flow uptake of nutrient or soil compaction reducing root mass may be the cause. This is why taking a soil test close to the sampling location of the tissue test is very helpful. If the tissue test is low and the soil test is low, there is a lack of supply. If the tissue test is low and the soil test is good, then there is a lack of access.

Getting a tissue test report back from the lab showing that both the “good” sample and “bad” sample have adequate nutrient concentrations to support plant growth does not mean the tissue test did not tell you anything. It means the issue affecting the growth of the “bad” sample is most likely not directly related to specific nutrient deficiency. Contact your ALG agronomy representative for support using plant tissue data in diagnosis situations.