News

Late Season Plant Tissue Analysis

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 later grain-fill 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 test 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 may not be 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.

Fertilizer Reference Samples

For fertilizer retailers and manufacturers, it is had been a best practice to retain a reference sample of all fertilizer deliveries. This practice can be very useful to producers that have on farm storage.  If an issue arises, a reference samples can be used to help identify causes and solutions. This is even more important today as we are sourcing fertilizer materials from new sources and at different times of the year. The reference samples area especially useful after the material has been applied and no more remains in storage. If you have any questions about fertilizer testing, please reach out to your ALGL regional agronomist.

Originally Published October 31, 2016

When fertilizer is applied to a field its nutrient analysis should match what is claimed on the fertilizer product label (ex. 28% nitrogen).  This means that the buyer gets what they want and pay for, and the supplier is paid for what they delivered.  This is almost always the case, but there are situations where there is a discrepancy.

When a fertilizer is offered for sale at any point in the supply chain (manufacturer, distributor, wholesaler or retailer) the seller and buyer need to be confident of the fertilizer analysis.  Samples are often collected and either immediately analyzed or retained in case a question arises.

We recommend each incoming load of fertilizer be sampled.  If the material is different from previous shipments (ex. color) it should be communicated to the supplier and a sample immediately sent for analysis.  Retain samples of normal-appearing materials in case a future question arises.  The length of sample retention is unique to each situation, but likely should be at least until the current crop is harvested.

Collection of fertilizer samples can be challenging, especially with bulk deliveries.  The state’s fertilizer inspector can provide procedures for sampling of various fertilizers:  liquid, granular, bulk, bagged, etc.  When your facility is being inspected it is a good practice to ask the inspector to provide you with a sample collected at the same time as the one they will have analyzed.  Should their sample show the fertilizer does not match the label the retained sample can be analyzed to independently confirm the analysis.

Retained fertilizer samples should be stored in air-tight containers to prevent moisture entry and spills.  Small 4–8 ounce plastic bottles work well for liquid fertilizers.  Solid fertilizers can be stored in zip-lock bags – compress the bag to remove air and then place in another bag.  Keep retained samples in a controlled temperature area.

Soil Testing In a Drought

Some locations in our trade area have experienced drought conditions and many of these areas continue to remain drier than normal.  If you are faced with sampling under drought conditions, the following information may assist you in your planning and the interpretation of the results that you receive.

Soil pH: Water pH readings may be 0.1 to 0.6 pH units lower than expected. This is due to a slight increase in soluble salts in the soil solution that haven’t leached into the soil profile. This condition does not alter the buffer pH result so the amount of lime recommended for most samples will not be affected. An exception to this would be sandy soils where the water pH determines the lime recommendation. However, sandy soils are leached more easily so the amount of soluble salts in solution may be much lower than a heavier soil.

Potassium: Soil test levels for potassium may be lower than normal. When soils remain extremely dry for extended periods of time, the moisture that normally keeps the clay latticework open for potassium exchange retracts, capturing the available potassium from solution. This will show up as a reduction in the soil test level. Also, potassium is easily leached from crop residue following harvest. With little rainfall, this potassium reserve could remain in the tissue. One caveat of this, though, is with inadequate moisture to produce normal yields, less potassium may be removed from the soil reserve.

Phosphorus: Soil test levels for phosphorus may be slightly lower than normal. The effect of the dry soil on phosphorus levels isn’t as dramatic as potassium, but less moisture in the soil may lower the soil test results. The same situation of reduced crop yields may result in less phosphorus being removed from the soil.

 Soil sampling technique: It is extremely difficult to sample dry soils. Often the top one or two inches of the core are compressed enough that some of this material may spill out of the probe. In minimum tillage situations, this could have a dramatic effect on the soil test readings. Also obtaining the correct depth of soil sample maybe difficult, auger soil probes tend to work better in extremely dry conditions.

Many of the areas that were suffering under dry conditions earlier in the season may have had enough time to equilibrate moisture levels prior to fall sampling so that some of the drought effects will be negligible. Reduced yields, though, will still be a remnant of decreased nutrients being removed from the soil. This year is one where soil sampling should occur to assess the effects of this unusual growing season.

Soil Sampling Season Preparation

The fall soil sampling season is upon us. Are you ready? Here are a couple of things you can do in advance of the sampling season to help things run smoother.

1. Call the lab, or your ALGL regional agronomist, to update your account if there have been changes in staff, email contacts, or phone numbers.
2. If you have made a change in software, call your ALGL regional agronomist so that they can modify your account settings to ensure that the data flow is correctly configured. It is also a good idea to do a test with a small sample number to ensure the data flows correctly and any needed changes in procedure are identified before the season starts.
3. Order soil bags and shipping boxes ahead of time. We are working hard to ensure that we have ample supply of sampling materials, but shipping delays could impact your access to supplies.
4. Check your UPS shipping labels, do you need more or have they expired. The expiration date is on the lower portion of your UPS labels, after this date the tracking of the package can become unreliable. If you need new labels call the lab or your ALGL regional agronomist and they can get new labels on the way.
5. Many customers are making the switch to Mehlich 3 soils data. If you have made the decision to switch or would like to make any changes to your reported data, contact your ALGL regional agronomist. The change to Mehlich 3 data can be made to your pdf reports, your data export files, or both.
6. Every January a summary of the previous year’s samples is posted to your eDocs account. That report shows what field by grower/farm/field that were sampled each year. For example, if you sample every two years, you can look back to the 2020 sampling report to ensure no resampling is missed.
7. If you are resampling for customers, take the time now to pre label the soil bags and pre generate labs submission forms.

Your ALGL agronomist representative is available to discuss you soil sampling protocols and help find way to streamline your fall soil sampling.

It’s Time to Evaluate our Management Decisions

By Stan Miles, Regional Agronomist

The time is drawing near when we will learn if the fungicide pass paid off or if our starter fertilizer choice worked or if we made the correct seed choice or was our fertility plan up to the task.  Have you been counting kernels, breaking ears in half and working the calculator on yield estimates?  The yield maps will tell the final tale but some late season scouting, sampling and note taking will go a long way when interpreting the yield maps and putting a star next to all the management choices that paid off.

My grandfather didn’t enjoy the benefits of yield maps and our site specific tools but he was a student of the game and he improved every year.  He had an excellent long term memory and added to his knowledge base every year. (1934 and 1936 were a bit warm I was told)

Several changes were made to our fertilizer plans last spring based on elevated product prices and there are many learning opportunities in our fields right now based on rate reductions, application timing changes and product substitutions that were done made to improve the crop budgets and remain profitable.

The Late Season Cornstalk Nitrogen Test is a useful tool that can help us evaluate how the corn crop finished the season and it can give us key insights into our nitrogen application rates and timings and it will help us determine if these practices were a wise choice and we can adjust next season. The Cornstalk Nitrogen test should be done between ¼ milk line and 3 weeks past black layer for most accurate results.  Sample an 8 inch segment of the stalk about 6 inches above the soil surface. It is recommended to collect about 10 stalk pieces randomly across a 10 acre area.

ALGL CORNSTALK NITRATE TEST (CSNT) factsheet can be viewed here.

The link above will take you to our fact sheet that describes sampling instructions, history and research that was used to develop the test and interpretations for the results.  Please contact your ALGL agronomist with questions and for more information regarding the Late Season Cornstalk Nitrogen test.

NPK from Summer Manure Applications on Wheat Stubble

Summer applications of manure to recently harvested wheat fields are a great option for managing manure volumes on a livestock facility. In an ideal situation, soil samples are collected following the wheat harvest and an agronomically appropriate rate of manure can be applied based on the future cropping plans for the field. However, we do not live in an ideal world. Whether the soil is too dry and hard to sample, or the manure pits are about to overflow, summer manure applications are often done without recent soils data to guide the rate. Here are some expectations and management tips for managing nitrogen, phosphorus, and potassium following a summer manure application.

Nitrogen in manure exists in two primary forms, ammonium and organically bound nitrogen. Depending on the type and storage method of the manure, the percentage of nitrogen in either form can vary greatly. The ammonium fraction is immediately plant available. While ammonium is relatively immobile in the soil, this form of nitrogen is easily converted to nitrate when soils are moist and warm which makes the nitrogen prone to leaching and denitrification. The organic fraction of nitrogen requires microbial decomposition to become plant available. A portion of the organic nitrogen will carry over to the next growing season. The relative amounts of organic and ammonium nitrogen forms are based on the type and handling of the manure.

• Characteristics of Poultry Manure
• Characteristics of Swine Manure
• Characteristics of Beef and Dairy Manure

Consider using a cover crop to help recover some of the plant available nitrogen to be released to a future crop when the cover crop residue decomposes. To help account for nitrogen that does carry over to the following growing season, use soil nitrate and ammonium testing so that an appropriate application of supplemental nitrogen fertilizer can be applied.

The general rule of thumb for managing phosphorus from manure, is that if you can keep the manure and soil on the field, you will keep the phosphorus as well. Cover crops do not take up an appreciable amount of phosphorus from a manure application, but they can help reduce runoff and erosion, keeping the phosphorus in the soil profile. Subsurface injection or light incorporation of the manure will also help minimize phosphorus losses. Collecting soil samples shortly after a manure application will not give you an accurate assessment of the availability of the phosphorus for the next crop. While there is no exact rule for how long to wait before soil sampling a manure field, most crop advisors would agree that you should wait 3 to 6 months to give enough time for the fresh source of phosphorus to come into equilibrium with the soil.

Potassium from a manure application is considered relatively immobile in the soil because it is a positively charge ion that can be held in the soil profile by the cation exchange capacity (CEC). Practices for minimizing loss of potassium and soil testing for it are the same as mentioned above in the phosphorus discussion. However, the soil’s ability to maintain potassium until the next growing season is going to be highly dependent on the type of soil the manure was applied to. Sandy, low CEC, and high organic matter soils have the lowest ability to hold potassium. If possible, select fields or sections of fields with more finely textured, higher CEC, soil to apply manure during the summer.

With the current price of conventional fertilizer, it is becoming increasingly necessary to not only utilize the nutrients in manure but to properly assess what is in the soil profile to avoid over applying any fertilizer.

Not All Manure is the Same – Beef and Dairy

The nutrient characteristics of a manure are dependent the species of animal, the diet of the animals, and how the manure is handled. While poultry manure is often viewed as a premium manure because of its high nutrient content per ton, and high organic nitrogen content, manure from the bovine species is not far behind.

The form of nitrogen in manure from beef and dairy manure vary bit and are dependent on manure handling. Solid beef and dairy manure are very high in organic nitrogen. Organic nitrogen is not readily plant available and requires microbial mineralization for the nitrogen to be plant available or subject to loss. Ammonium nitrogen volatilization loss from stock piling solid beef and dairy manure is small.  Low moisture solid beef manure without beading can have higher nitrogen content than swine or poultry manure and can release slowly like the poultry litter.

Source: University of Minnesota

Liquid beef and dairy manure can be quite variable in nitrogen content and form. Using “book values” for liquid dairy and beef are not advisable as they can be even more variable than liquid hog manure. The relative amounts of ammonium and organic nitrogen are dependent on manure handling and is not predicable.

Dairy and beef manure are unique in that they have relatively low phosphorus content and relatively higher potassium content ac compared to nitrogen than other manures.  Potassium levels are overall higher than other manures or organic materials.

Source: Iowa State Extension, 2016

Optimum utilization of manures is dependent on the characteristics of the manure. Beef and dairy manure tend to have the slowest nutrient release assuming that the nitrogen is mostly in an organic form. Only 30-50% of the nitrogen is available in the first year and can take up to 3 years to fully release. Poultry releases 50-60% in year one and swine released 90-100% within weeks. Even the phosphorus release from beef and dairy manure is up to 10% slower than other manures. With the variability of liquid beef and dairy manures it is advisable to test manures for total, organic, and ammonium nitrogen to better understand how it will perform in your situation.

There is one unique management issue with dairy manure from sand bedded dairies. In many parts of the upper corn belt and northeast, the sand used for bedding is not silica based but rather fine limestone. Depending on of efficiency the sand recovery is from the manure stream will impact how much limestone is being applied in the manure. Repeated applications of dairy manure with bedding sand can lead to elevated soil pH levels over time. Ask your ALGL regional agronomist on how you can add CCE (calcium carbonate equivalent) testing to your manure tests to determine the impact manure applications on soil pH.

Sources:

Lorimor, J., W. Powers, A. Sutton. (2004). “Manure Management System Series. MWPS-18, Section 1 - Manure Characteristics.” 2^nd ed. Midwest Plan Service, Iowa State University.

Properties of Manure, Manitoba Agriculture, Food and Rural Development, November 2015.

University of Minnesota, Manure Characteristics, https://extension.umn.edu/manure-management/manure-characteristics#nitrogen-817860

Using manure Nutrient for Crop Production, Iowa State Extension, 2016

Interpreting Soil Nitrate and Ammonium Levels Beyond PSNT

Most growers and crop advisors are familiar with interpreting soil nitrate data when it is being used to determine a rate of nitrogen to apply at sidedress. The problem with PSNT interpretations is that they are only intended to be used in situations where the only form of nitrogen applied to the soil up to that point is manure and is done when the corn is V4 to V6. (For more information about PSNT, please visit our previous blog post.) With the ever-increasing access to late season nitrogen application options, it is necessary to utilize soil test data to better determine a rate to apply after commercial fertilizer has already been applied. Tissue testing is valuable in monitoring crop nitrogen levels, however has limitations. (For more information about tissue testing for nitrogen management, please visit our previous blog post.)

As with any nitrogen model or prediction, there will always be a level of uncertainty due to the highly variable nature of plant available nitrogen resulting from the influence of weather and soil microbiology. However, a few years ago Purdue University proposed an approach to assess soil test of nitrate and ammonium especially in seasons where there is a higher chance of nitrogen loss. (Please see the entire article here. http://www.kingcorn.org/news/timeless/AssessAvailableN.html).

The general idea is that you can add the ppm of NO3-N and NH4-N together and multiply the total by 4 to estimate the total available nitrogen in pounds per acre, assuming the data is from a 12-inch-deep sample. We advise to test for both nitrate and ammonium to have a more detailed nitrogen inventory and to help determine future nitrogen availability.  (For more information about nitrate and ammonium soil testing, please visit our blog post.) For example, if a sample was collected near tasseling, and the soil test results showed that there is 10 ppm NO3-N and 5 ppm NH4-N, you can estimate that there is approximately 60 pounds of nitrogen still available to the crop. To make a decision with this data, you have to determine how much more nitrogen might be needed to achieve your yield potential. At the time of tasseling, a corn crop has taken up approximately 60% of its nitrogen requirement. If the field that has a potential of 250 bushels, that means it has already taken up about 150 pounds per acre (assuming 1 pound of nitrogen per bushel). This crop could be about 40 pounds short to reach the yield potential. Had the same soil test results come from a field with a 180-bushel potential, it would suggest that there is enough nitrogen to finish out the season.

If you need helping making sense of late season nitrogen samples, contact your ALGL agronomist.

Why Test Soils for Both Nitrate and Ammonium?

What is the value of testing soil for both nitrate and ammonium nitrogen when many of the interpretations, like PSNT for manured fields, only utilize nitrate values? Why test for ammonium when we can assume that all of the available nitrogen in the soil has converted to nitrate? The answer depends on the way the data is being utilized.

Nitrogen in the soil can take several forms, but plants can only utilize ammonium and nitrate. Ammonium is stable in the soil until it converts to nitrate which is mobile in the soil, and subject to loss via leaching and denitrification.

Nitrogen in manure starts as organic nitrogen, that material mineralizes to become ammonium, and then degrades to nitrate. Manures at application time will be a mix of organic nitrogen and ammonium depending on species and manure handling. Poultry and beef manure tend to contain more organic nitrogen, while dairy and swine liquid manures tend to have a higher ammonium content. While this can be measured, we cannot accurately predict the rate of conversion from organic nitrogen to ammonium, then to nitrate in the soil. When testing soil after a manure application, nitrate can be used for traditional PSNT interpretation assuming continued future release of nitrate from ammonium. By measuring the ammonium in the soil that assumption can validate or disprove this assumption. Natural soil ammonium levels are below 4 to 6 ppm. Soil test ammonium results at sidedress near, or below these levels, indicate that future release nitrogen release from the manure maybe limited and increased nitrogen rates may be warranted.

Inorganic fertilizers convert from urea to ammonium and then to nitrate. Commercial fertilizers can start at any three of these levels, UAN starts at all three. Testing for nitrate only can miss a large fraction of the available nitrogen in the soil. There are commercially available nitrogen conversion inhibitors to reduce the rate of conversion from urea to ammonium and ammonium to nitrate in the soil. Without inhibitors the conversion of urea to ammonium and ammonium to nitrate occurs quickly depending on soil moisture and temperature. Over a matter of few days to weeks. More information on using nitrate and ammonium soil tests to manage in season nitrogen applications can found on in the ALGL Newsletter. (link to article)

The conversion of ammonium to nitrate can also be inhibited by soil conditions. As soil moisture increases in warm soils, the rate of conversion from ammonium to nitrate increases. However, at soil saturation the conversion of ammonium to nitrate can stop while nitrate continues to leach and denitrify. Extremely dry or cold soil conditions can prevent both the conversion of ammonium to nitrate and the loss of nitrate.

As an example, following a recent wet spring, the ALGL agronomy staff worked with a grower that tested for nitrate only. The grower was trying to determine how much of the anhydrous ammonium they had applied spring preplant had been lost. The resulting nitrate values were very low indicating that nearly all of the applied nitrogen was lost. When the ammonium test was performed on these same samples the data values were high, high enough to indicate that all of the nitrogen remined in the ammonium form. The saturated soils prevented the conversion of ammonium to nitrate for 10 weeks, the ammonium test data defied the assumptions made in this situation and avoided an unnecessary nitrogen application.

Rather than assuming how much ammonium has converted to nitrate or assuming that there is more ammonium to convert to nitrate in the future, the most accurate way to manage these situations is to test the soil for both ammonium and nitrate.

Mid-Season Nitrogen Management Tissue Test vs. Soil Test

Some places in our trade area experienced heavy rainfall in the weeks following planting and it is likely that nitrogen was lost in these saturated areas. Plant color has improved overall but some of the stressed areas might benefit from additional nitrogen applied later in the season to help finish the corn crop. Extended dry weather after crop establishment in some of our trade will improve the soil retention of nitrogen and may reduce plant availability.

Plant tissue sampling up until 2 weeks past tasseling can help monitor the condition of the crop and indicate when plants are struggling to access needed nutrients to support the rapid growth phase of development.  When interpreting plant tissue data, it is important to remember this reveals a snapshot in time and does not offer predictive value of future condition of the plants.  Soil nutrient levels and future weather conditions have a large impact on late season nitrogen availability.

When paired with soil nitrate and ammonium levels, a better picture of the overall conditions will become apparent.  Given the current cost of Y-drop UAN applications, UAN fertigation, and urea top dress treatments these two testing methods will help guide these in-season decisions. For more information on using soil test nitrate and ammonium to determine late season nitrogen applications see our blog post.

Please contact your ALGL agronomist for assistance with mid-season nitrogen testing.