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.
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.
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.
Lorimor, J., W. Powers, A. Sutton. (2004). “Manure Management System Series. MWPS-18, Section 1 - Manure Characteristics.” 2nd 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
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.
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.
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.
Early season field scouting is essential to ensure good emergence, detect potential weed and insect pressure, and monitor the effectiveness of your fertility program. The earlier an issue is detected, the better chance there is to correct the issue. One tool to help detect potential fertility problems is plant tissue analysis. However, to get useful results back from the lab, the proper plant part must be collected for the current growth stage of the crop.
The proper method for collecting early season corn tissue samples is to collect 15 or more whole plants to comprise a single sample. This is only referring to the above ground portion of the plant. This method is appropriate for corn up to 12 inches tall, or V4. However, corn can be sampled too early to provide useful data for making decisions. During the first three weeks after emergence, much of the nutrient content of the young plant is not coming from the soil, but from the embryotic tissues within the seed. The young plants also have a very small seminal root system during the first few weeks which are not able to access the nutrients in a large volume of soil, the main role of this root system is to get water to the seed and new leaf tissues. Nutrient deficiencies during the first few weeks are likely caused by environmental conditions and do not necessary reflect low nutrient levels in the soil. An example of this situation is young corn plants turning purple. Purpling of young corn plants can be a symptom of a phosphorus deficiency but can also occur on soils with adequate phosphorus levels when nighttime temperatures are low. Cool spring nights slow metabolic processes in the plant resulting in the buildup of anthocyanins, which appear purple. Tissue sampling in corn should be delayed until 3 to 4 weeks after emergence, or until the plants have developed a functional nodal root system to ensure that the tissue analysis is representative of the nutrients that are available to the plant.
Image: V4 corn plant showing purpling. Source: Purdue.edu
Like corn, soybeans can also be sampled too early. Proper tissue sampling for all growth stages for soybeans is collecting 25 or more of the most recently mature trifoliates without petioles. The first leaves to appear on a recently emerged soybean plant are unifoliates, or cotyledons. The nutrient content of the cotyledons, sometimes referred to as seed leaves, does not accurately represent the nutrients available in the soil. Tissue sampling in soybeans should be delayed until the V2 growth stage. The V2 growth stage is reached when the second trifoliate has completely unrolled. It will generally take a minimum of 3 to 4 weeks after emergence to reach this stage. At this point, the first trifoliate is considered mature, and can be collected for tissue analysis.
Image: V2 soybean plant. Source: Clemson.edu
Spring tissue sampling of winter wheat can be a very useful management tool. The timing of wheat sampling does not correspond to a specific growth stage though. The important factor when determining the appropriate time to sample wheat is that the wheat has broken dormancy and is actively growing again. Generally, wheat will be at a growth stage of Feekes 3 or 4 when this occurs. The appropriate method for collecting wheat samples at this stage is to collect 25 or more whole plants from ½ inch above the soil surface. One of the benefits of early season wheat sampling is to fine tuning a “green-up” nitrogen applications based on the nitrogen content of the plant at Feekes 5 (please visit the Purdue Extension News Release for more information).
Image: Feekes 5 wheat. Source: Kansas State University
Accurate plant tissue testing begins with proper sample collection and handling. Make sure to collect the proper plant part for the current growth stage of the crop and collect the proper number to make the sample. This information can be found on the plant analysis page at algreatlakes.com. Always avoid soil contamination in your plant samples. Package samples in paper bags. If shipping is delayed, store samples in a cool location, but do not freeze. Never include roots with a plant sample. If you have any questions on proper plant tissue sampling, please contact the lab for assistance.
Many acres of corn across our area are established with good stands and it is on its way into the summer growing season. Soon it will be time to apply side-dress nitrogen and concentrate on the nutrient needs of the crop and prepare it for the rapid growth phase that is soon approaching.
Given the increased price of nitrogen and the strong crop prices that are available some of our customers are considering a more intensive pre-sidedress nitrogen testing program to help them better place their fertilizer dollars where it has the best chance of making the greatest impact on harvested yield. Based on university data across the midwest it is strongly recommended that sample cores for PSNT be collected at a 12” depth to capture more of the mobile nitrogen as it begins to move downward through the soil profile. For those interested in increasing the intensity of their sampling program it may be useful to collect PSNT samples on a 5-10 acre grid or zone pattern of 8-12 cores per sample.
It may be most useful to concentrate sampling efforts on fields with historically medium to high yield potential with good plant stands and fields with likely variable levels of nitrate availability such as areas that have had applications of manure, municipal waste and other organic forms of nitrogen.
It may be advantageous to adjust nitrogen application rates based on actual measured nitrate levels in the soil at side-dress time. If you have questions or would like assistance with your pre-sidedress nitrate testing plan please contact your agronomist at A&L Great Lakes Laboratory and we would be happy to assist you.
Potassium (K) soil test levels have the greatest potential to vary between fall and spring. Soil test K levels are usually lowest in the dry conditions of late summer prior to harvest and peak in the early spring. Potassium is released from crop residues as the crop matures and crop residues degrade, and this release continues through the winter months. In addition, potassium can be released from the soil through prolonged saturation and freeze/thaw cycles in the winter months. With these processes combined, the question becomes how much higher soil test potassium levels will be in spring- versus fall- collected samples.
A simple approach is to select a location in a field such as a grid or zone sample location and physically mark it with a flag. Collect 6-8 cores at a depth of 6-8”. It is important to pull the same number of cores at the same depth each time samples are collected. Collect the cores as close as possible to each other and the flag. Do this in the fall and in the spring.In most cases, spring and fall potassium levels are usually within 5-10%. Spring soil sampling does not always result in higher potassium soil test level; this depends on crop residue release and weather patterns. Below is an example of some actual field data collected in northeast Indiana in a clay loam soil with a corn/beans/wheat crop rotation with fertilizer applied after the spring sample collection. The key to proper soil sampling is consistency. Sample the at the same depth, following the same crop at the same time of year.
As producers work through the various budgets for the 2022 crop year there is one calculation coming up in a few weeks that shouldn’t be overlooked. Wheat grain prices have been very strong recently, but if you are faced with the decision of whether to remove the straw or leave it in the field, take a few minutes to update the value of the nutrients that would be removed with the straw and make sure you are adequately compensated for the replacement costs.
The Ohio State University tells us that a well grown wheat crop will yield about 2.5 to 2.8 tons of straw. Data shows that a ton of wheat straw contains about 11 lbs of nitrogen, 3 lbs of phosphorous and 20 lbs of potassium. When we apply today’s fertilizer prices to the nutrients removed we can quickly approach $95.00/acre.
Compared to past fertilizer prices that placed the value of straw at around $17.00/ton the current value of the nutrients places the price closer to $35-40/ton. 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 more accurately estimate the nutrients removed and assist you with your calculations.
With nitrogen prices hovering around $0.80 per unit, deciding when and how much to apply is becoming increasingly difficult. Below are some tips to help make the most of your nitrogen program.
Do not skip the starter. Research has shown the benefits of applying 20-30 pounds of N at planting. Starter should even be considered on manured fields. Cold soil temperatures early in the season prevent the mineralization of N from organic forms. A corn crop that starts behind due to lack of N is not likely to maximize yield at the end of the season.
Split applications of N into as many passes as feasible. The more frequently N is applied, the more efficiently it can be used. Explore late season options for application. A corn crop takes of 60-70% of its N requirement by tasseling. If 70% of the N is applied between starter and sidedress, any additional applications can be fine tuned based on the performance of the crop at that time.
Soil test for N (both nitrate and ammonium), even on non-manured fields. Using a PSNT to adjust sidedress rates is common practice but using soil tests later in the season to evaluate a nitrogen program is less common because there is no clear interpretation of the results. However, this data especially in the hands of a trained crop advisor, can be a useful piece of the puzzle that is N management.
Use tissue tests to help fine tune an appropriate late season application rate or possibly determine if the application is needed at all. Collecting tissue samples 2 to 4 times during early growing season can help to monitor how efficiently the crop is utilizing the N that has already applied. If N was applied at a rate assuming an average growing season and yield, but conditions are favorable for a higher yield, a tissue test can help determine if a higher rate of N is needed to produce that higher yield.
Most importantly chose an appropriate yield goal based on the history of the field. Applying additional N to a field that has other limitations such as drainage problems or low fertility will likely result in financial loss. Also remember that maximizing yield does not mean maximizing profitability. To help fine tune an appropriate N rate for your area and N prices, use the Maximum Return to Nitrogen calculator available at http://cnrc.agron.iastate.edu/.