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"Good" Vs. "Bad" Tissue Test Data

Tissue samples are submitted to the lab with the sample ID ‘s of “good” and “bad”, and often the tissue test data results are very similar. Sometimes the “bad” sample will have higher nutrient concentrations than the “good” sample.

Tissue test data is a concentration of a given nutrient within the plant biomass. The concentration is the relative amount of a given nutrient within a defined volume of plant biomass.

Impact of nutrient uptake and plant size on tissue test results.

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. Observation notes and pictures taken at the time of sampling can be very valuable in interpreting plant tissue data.

Getting a tissue test report back form 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 nutrient related. Contact your ALG agronomy representative for support using plant tissue data in diagnosis situations.

High Soil Nitrate Levels on PSNT’s

Over the last few weeks, we have received many soil samples for nitrate analysis to help determine what rate of nitrogen to sidedress in corn. Several of the samples have generated questions for our agronomy staff regarding unusually high nitrate results. Upon further investigation we have found that many of these fields with high nitrate levels have one thing in common, they had manure applied since the previous crop was harvested. This is the exact scenario that the pre-sidedress soil nitrate test (PSNT) was developed to assess. Each university extension program in the Great Lakes region have developed interpretations for determining what rate of nitrogen to apply based on the soil nitrate level, and they all basically agree that if it is above 25 ppm, no additional nitrogen is needed. This year it has not been unusual to see 50 to 100 ppm.

Where is all this nitrogen coming from? Simply stated, we can thank the fall, winter, and spring weather. Last fall was dry, which allowed for timely manure applications. The winter was relatively dry and cold. This kept the microbial activity to minimum reducing the chance for nitrification and mineralization to occur that could lead to nitrogen losses. The early spring was cold through most of May, again minimizing nitrogen losses. Then early June got hot with some rain, and it kicked the microbes into high gear converting ammonium and organic nitrogen sources into nitrate.

So, what do we do with these high numbers? Most growers who use manure as part of their nitrogen program know that even an aggressive fall manure application will likely run short on nitrogen and generally require a supplemental source to get through the whole season. Even though the university interpretations say there is more than enough, you need to consider each situation on its own. Irrigated ground with a 300+ bushel potential is certainly going to require much more nitrogen than dry ground with 150 bushel potential. Is there an option for late season applications, such as fertigation or a high clearance spreader? If you are in a situation where your current soil test nitrate levels do not justify a sidedress application, your best bet is to monitor the crop. At tasseling, a corn crop should have taken up 60 to 70% of the nitrogen it needs for the season. Collecting a plant tissue sample at this time can potentially identify a nitrogen deficiency before any visual symptoms appear.

If you have any questions or want to discuss your own situation, contact your ALGL representative.

Tissue Sampling for the Future

The ALGL agronomy staff is regularly quizzed about the value of tissue testing. Often the focus is to verify a visual nutrient deficiency, then determine what foliar fertilizer to spray.  While this is a valid application of the management tool, there are greater benefits to be had by using the information to avoid the issue in the future.

Think of the tissue test as a report card for your overall crop and soil fertility management plan. With a tissue test collected just before and during key physiological growth periods of the crop can help find week points in the overall soil/crop fertility plan. If a deficiency is found a quick rescue maybe the applications of a soil or foliar fertilizer, but how do you avoid the same situation occurring in the future? The greatest value in tissue testing is not only identifying a fertility issue and correcting it now and adjusting in your soil/crop fertility management plan to avoid the recurrence of the situation, while using routine soil and tissue testing to verify the correction of the issue.

A simple example. You notice areas of your soybean field showing interveinal yellowing of younger leaves. The tissue test confirms that the plant is deficient in manganese. The quick response is a foliar application of manganese to correct the issue. A soil test collected at the same time as the tissue test shows low levels of manganese in the soil, so the cause of the plant deficiency was due to the soils inability to supply the nutrient. The foliar application addresses the symptoms, but not the cause. Without proactively addressing the soil fertility issue along and/or planned foliar applications, the issue most likely will reoccur in the future.  The knowledge from the tissue and soil test can help drive changes in the crop/soil fertility plan to avoid the issue in future years in conjunction using tissue and soil tests in future crop season to confirm the change in the plan continues to correct the issue.

Improving N Use Efficiency with PSNT

The goal of any good nitrogen (N) management program is to maximize yield and minimize inputs. For corn growers that utilize manure or other organic forms of N, using the Presidedress Soil Nitrate Test (PSNT) can be a good tool for fine tuning N needs of the crop prior to sidedressing with N.
 
The PSNT is a way to measure the amount of N, in the form of nitrate, which is supplied by organic materials in the soil. The procedure was developed to measure the amount of N that is naturally released, or mineralized, from the decomposition of organic materials in the soil. This test is  applicable in fields where manure has been applied, following legume forage crops, or following cover crops.
 
Sampling for the PSNT is different than routine soil sampling. Samples are collected approximately 1 week prior to a planned sidedress application, generally when corn is 6 to 12 inches tall (V4 to V6). Samples are taken to a depth of 12 inches. Take 10 to 15 cores to represent one sample area. Sample area should be determined based upon factors that influence mineralization rates such as drainage class, slope, cropping history, and rate of manure applications. A single sample should represent no more that 15 to 20 acres. The samples should be shipped immediately to the lab for analysis. In situations when shipping is delayed, refrigerate or freeze samples until they can be shipped or delivered to the lab. Samples should be shipped early in the week to avoid weekend delays.
 
We understand the importance of PSNT in your nitrogen management programs, so we provide one day turnaround time for soil nitrate samples.
 
Most states have developed interpretive guidelines for the PSNT. While most states have very similar interpretations, we recommend looking into other states in the region to help guide you to make the best management decision for your operation.

As mentioned previously, the PSNT is intended to measure the N from organic matter decomposition, so if a high rate of N was applied pre-planting, the interpretation of the results may not be accurate. For additional information on PSNT from A&L Great Lakes Laboratories, please see our Fact Sheet.
 
Links:
 
Indiana: Purdue Extension
Ohio: Ohio State University Extension
Michigan: Michigan State University Extension
Illinois: University of Illinois Extension
Wisconsin: University of Wisconsin Extension
A&L Great Lakes Labs Fact Sheet: In-season Soil Nitrate Testing for Corn

What is Driving Fertilizer Prices?

It is no surprise to those farming or in ag retail that fertilizer prices have been going up. In the past year nitrogen prices have increased an average of 36%. Urea is up 31%, anhydrous ammonia up 39%, and 28% UAN is up 45%. When looking at the cost of an individual pound of nitrogen from these products the gap grows. In March of 2020, the cost was $0.30/pound of nitrogen for anhydrous ammonia and $0.42/pound of nitrogen for urea and 28% UAN. Fast forward to March 2021, we are at $0.42/pound of nitrogen with anhydrous ammonia, $0.55/pound of nitrogen with 28% urea, and $0.61/pound of nitrogen with 28% UAN.

So,  are fertilizer manufactures trying to get their part of the grain rally? Maybe not. Fertilizer price increases started back last fall with MAP and DAP prices beginning to rise in September of 2020. Potash began its climb in December of 2020. Nitrogen hung back and started its big climb in February 2021, according to Progress Farmer DTN’s data. Looking back the rally in grain prices started gaining noticeable momentum in September/October of 2020. This seems to correlate rather closely with rally in grain prices on the surface. While this seems more than coincidental, fertilizer prices do not move that quickly, there is couple month lead time on fertilizer price changes.

Ag retailers began seeing tightness in supply and were forecasting price volatility of fertilizer in the middle of 2020. By late-summer 2020 retailers were talking to customers about prepaying fertilizer, especially nitrogen, to offset potential fertilizer price increases before the grain rally began.

The strong yields, government payments, and the grain commodity price rally led to strong farm incomes in the fall of 2020. This additional income then led to strong and swift increase fall fertilizer sales. Favorable fall weather for the first time in several years also allowed ample time for fertilizer to be spread and fall tillage to be completed. This complex led to a rapid realization of pent-up demand for fertilizer. It was a race to keep fertilizer in the warehouses to meet this demand. At the end of harvest many fertilizer warehouse inventories were low to exhausted. The fertilizer infrastructure was impacted by simple supply chain disruptions like other markets, and reduced product forecasts based on downward sales projections from the past few years, started to tighten supply and initiate the price increase in the summer of 2020. The good yield and commodity prices added the fuel to the fire. The unexpected demand for fertilizer created by farmer buying, combined with strong worldwide demand in a tight supply market, is driving the fertilizer prices higher.

So, what can be done at the farm gate to manage this? Yes, the grain markets are strong, and the extra income can cover this extra cost. But do you have grain to sell at these higher prices, or did you sell straight out of the field last fall or locked in prices too early in the rally? Would you like to hold on to some of the extra profit in 2021 to shore up your cash position? It is in times like these that solid crop fertility management can help achieve your financial goals for you faming business. Your ALGL regional agronomist is ready to help you achieve your business goals, and your customers business goals, by getting as much as you can out of every dollar spent on crop nutrition.

Not All Manure is the Same – Liquid Swine Manure

The nutrient characteristics of a manure is dependent the species of animal, the diet of the animals, and how the manure is handled. In recent years crop managers have been advancing the use of liquid swine manure from waste product to nutrient source. To efficiently utilize the nutritional benefit of liquid swine manure takes a bit of management.

The nutrient content of liquid swine manure is less concentrated than other manures which adds additional handling challenges handling large application volumes per acre. Effective manure management of liquid swine manure starts well before the day of application. The greatest variable in liquid swine manure is moisture content. The moisture content of liquid swine manure is mostly dependent on external water sources. Excess drinking water loss to barn manure pits, wash water from the barn, along with rainwater additions to open exterior pits increases water content of the manure resulting in a dilution of nutrient content. Reduction of external water making its way into storage pits and lagoons can help reduce dilution. In pits and lagoons, the solids settle to the bottom of the pit or lagoon creating a stratification of manure moisture content with depth.  As much agitation as can be safely achieved at application time can help reduce variability in the nutrient content of the applied manure.

Most of the nitrogen in liquid swine manure is in an ammonium form rather in organic forms. The amount of organic N is directly related to the solids content in the manure, which is usually low. The solid fraction separated from whole manure or cleaned from the bottom of a lagoon/pit after settling, can have more organic nitrogen than ammonium.  Any organic forms of nitrogen in manures need to be mineralized into inorganic ammonium before becoming plant available, this additional step in making organic nutrient forms plant available further slows the release to plant and help reduce potential losses. Especially in cold soils which are not conducive to microbial activity needed to break down the complex organic molecules. The ammonium form of nitrogen is held by the soil cation exchange capacity (CEC) and is directly available to plants for use and to soil microbes for conversion to nitrate. Ammonium is subject conversion to nitrate and possible loss in warm (over 50⁰F) and moist soils. For fall and early spring liquid swine manure applications, ammonium nitrogen stabilizers can be added to reduce/delay the conversion of ammonium to nitrate.

If liquid swine manure is applied in the fall before the soil temperature falls below 50⁰F, or if a period of warm temperatures occurs in the spring prior to planting allowing soils to warm up above 50⁰F for period of several days, non-stabilized ammonium nitrogen can rapidly convert to nitrate and become subject to loss. If these conditions occur when the manure was applied as a planned nitrogen source for corn, it is highly recommended to perform a presidedress soil nitrate test (PSNT) to evaluate soil nitrogen levels and the need for supplemental nitrogen. Given that most of the nitrogen in liquid swine manure is plant available at time of application makes liquid swine manure a good nutrient fit for side-dressing corn, and top-dressing winter wheat.

Most of the phosphorus in liquid swine manure is in an organic form so the concentration of phosphorus is directly related to the solid content of the manure. Liquid swine manure phosphorus content increases with increasing solids content. Potassium is water soluble in the liquid fraction and the concentration remains relatively constant regardless of manure solids content.

Ammonium nitrogen, soluble phosphates, and potassium contained in liquid swine manure are highly water soluble and contained within the liquid fraction of the manure. Off-site movement of liquid swine manure nutrients could occur rapidly if surface applied to the soil without incorporation, applied to areas of the field prone to concentrated surface flow, close to open drains/ditches, shortly before heavy rains, and to frozen or snow-covered fields. Incorporation of liquid swine manure greatly increases the retention of nutrients and reduces odor.

Nutrients targeted in feed rations can become elevated in the manure. High concentrations of zinc used in nursery feeding often leads to elevated zinc levels in manure. Repeated application of high zinc manures on the same field can lead to elevated zinc soil test levels. Some zinc is beneficial to crop growth, especially corn, however elevated zinc levels can lead to reduced plant growth.

Sources:

Chastain, J.P., J. J. Cambarato, J. E. Albrecht, and J. Adams. (1997). “Swine Manure Production and Nutrient Content. Swine Training Manual.” (pp 3-1:3-15). South Carolina Cooperative Extension.

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.

What Tissue Test Will and Will Not Tell You

Tissue testing has long been utilized as a diagnostic tool but is increasingly being used as part of the overall crop fertility management. This concept is helping agronomists and growers find more effective and efficient ways to provide plant nutrition. It is easy to read too deeply into tissue test result, while missing basic issues. There are a couple of basics to keep in mind when reviewing plant tissue data. In many cases, observation of the crop leading up to sampling is key.

Less than 15% of the plant dry biomass is represented by tissue test data. Much of a plant dry biomass is carbohydrates comprised of carbon, hydrogen, and oxygen that is not reported in the tissue test data. As the carbohydrate content of the plant goes up, the percentage of the plant represented by the nutrients on the tissue test decrease.  A plant that is stunted or stressed due to environmental impacts that do not directly impact the update of nutrients can result in overall normal to high tissue test data values.

Plant growth patterns can impact tissue test data. Just prior to a rapid growth phases, plants accumulate nutrients in preparation. At this point tissue test results tend higher. Once the plant enters the period of rapid growth, the plant begins to accumulate carbohydrates very quickly. These additional carbohydrates effectively dilute the nutrient content of the plant biomass. These growth patterns can also shift the mobile nutrients in, and out, of the plant segment being sampled.

A tissue test is a snapshot in time. It is an evaluation of the nutritional status at the time of sampling. This will reflect the nutrients the plant was able to access in the past but does not give any indication at to predicting nutrient values into the future. This a key reason why management systems with a defined focus on tissue testing a part of an overall fertility plant promote repeated sampling of the same area through the growing season.

Repeated tissue testing of the same area can show how any seasonal patterns and plant development may impact the crops’ ability to access nutrients through the growing season. To make valid assessments of the tissue data, weather data, along with crop observations, are key. For example, periods of dry weather can reduce nutrient availably to the plant, soil water is essential in nutrient movement to and into the plant. Dry weather with normal growth, resulting in normal carbohydrate accumulation, will normally lead to slightly lower nutrient vales in tissue tests, especially nitrogen and potassium. If the dry weather is severe enough to effectively stop plant growth, resulting in reduced carbohydrate accumulation, the tissue test could come back normal to high.

A tissue test can tell you what nutrient is missing in the plant but cannot tell you why. Was the plant unable to access the nutrient, or was the soil void of the nutrient? Often the first instinct is to apply the nutrient that was low in the tissue test. In this situation it is recommended to retest later to see if the nutrient application corrected the issue. A second recommendation is to take a soil test from the same sample locations as the tissue samples to identify if the nutrient is low in the soil or could something like soil pH be impeding the availability of the nutrient.

Do not get too wrapped up in ratios of nutrients in the plant. If a nutrient included in the ratio is deficient, the ratio will be skewed towards the opposite value. This can be seen with or without a calculated ratio if target for normal levels for a given nutrient are included. Ratios do help bring attention to these variances. For example, if one of the nutrients in the ratio is very close to the bottom of a normal or target level, while the other is high the ratio may alert you to abnormality a bit sooner than looking only at the individual nutrient ratings. The reporting of a ratio does not specifically mean there is an interaction between the nutrients.  A good analogy is a brick wall. A brick wall has a defined ratio of mortar and bricks. If you have more bricks, you cannot build any taller of a wall, and the extra bricks don’t impact how much mortar it takes to build the wall.

Trying to predict yield or any future values from tissue testing is difficult. There are more factors than plant nutrition that can impact plant growth and the final yield. If you are looking to start plant tissue test monitoring this growing season, contact your ALGL regional agronomist for details on our plant monitoring program before the sampling season begins. Contact your ALGL regional agronomist with any other questions or tissue testing needs.

How Quick Can I Expect Pelletized Lime to Change Soil pH?

Can I apply pelletized lime at planting and expect it to address my low soil pH rapidly in-season? While pelletized lime provides many benefits, such as quickly altering soil pH and possessing handling qualities that can make the application of the product more versatile, it has some limitations.  

A traditional pelletized lime is a uniformly finely ground lime that has been pelletized using a binding agent. The chemical makeup of the lime material, final grind, and the binding agent can impact the rate of soil acidity neutralization. All these factors influence the rate in which the carbonate material becomes water soluble, and reactive with hydrogen ions, to neutralize the acidity. Likewise, the rate of reaction is impacted by soil incorporation and soil moisture.

The figure below (Jones and Mallarino, 2018) shows the relative rate of acidity neutralization as impacted by the fineness of a calcitic ag lime. If only the finest ground particles were applied to the soil, the rate of soil pH adjustment would take place quicker than a blend of particle sizes. In addition, the pelletizing of the finely ground lime greatly increases the uniformity of spreading and handling characteristics in fertilizer systems designed to handle granular fertilizer.

This data was generated from an experiment conducted in a laboratory to control the environmental factors/conditions so that the research is repeatable. Primarily maintaining a constant soil temperature and moisture at 80-90% of field capacity. If we were to move this study to a field, fluctuations in temperature and soil moisture would impact the data. Lower soil temperatures and drier soils would slow the rate of reaction, especially for the more finely ground fractions.

The figure below from the same study (Jones and Mallarino, 2018) shows the relative rate of acidity neutralization as impacted by the product used. The results of the pelletized lime closely follow the results from the 60-100 mesh grind. Faster than traditional ag limes, but still slower than pure calcium carbonate when applied at equal rates.

Both the pelletized lime and the calcitic lime has similar pH impacts for the first 21-35 day of this experiment as the finely ground portion of the calcitic lime reacted similar to the fine grind of the pelletized lime.

This figure also shows that while pelletized lime increases soil pH more than calcitic lime when applied at equal rates, it also takes pelletized lime in excess to 100 days to reach a maximum soil pH adjustment. That is a over 3 months, or slightly longer when taking field environmental factors into consideration. If the pelletized lime is applied at planting the first of May, maximum pH will be achieved the bringing of August at the earliest. By this point in the season altered nutrient uptake and growth may have already negatively impacted crop yield.

If pelletized lime is routinely applied every year, timing is not critical. If this is a recue application of pelletized lime to make a quick pH adjustment to a neglected field to avoid yield loss, fall to late winter application of the pelletized lime prior to the growing season will have a bigger impact on in-season soil pH levels when compared to an at-planting application. While pelletized lime is a very useful tool in fertility management, it still takes time for pelletized lime to make meaningful soil pH adjustments.

Source: Jones, John D., and Antonio P. Mallarino. “Influence of Source and Particle Size on Agricultural Limestone Efficiency at Increasing Soil PH.” Soil Science Society of America Journal, vol. 82, no. 1, 2018, pp. 271–282., doi:10.2136/sssaj2017.06.0207.

Checking for Consistency from One Sampling Event to the Next

Most progressive precision soil sampling programs are sampling fields on a 2- or 3-year cycle. Often in the course of 2 to 3 years, there have been changes in the personnel or equipment used to collect those samples. There are a few clues in your soil test results that can be examined to validate if those samples were collected consistently.

The first clue to check is the organic matter level. The organic matter has the least potential to change significantly over the course of a few years. Even under intensive management to increase organic matter, such as no till, cover crops, and residue management, it is unlikely to see the soil test level increase by more than 0.1% per year on average. Any drastic change in organic matter levels likely indicate inconsistent sample depth, contamination of the sample with crop residue or manure, or an inadequate number of soil cores being collected to make up the sample.

The cation exchange capacity (CEC) should remain relatively consistent from sampling event to sampling event. The CEC is a measurement of the negative charge in a soil which comes from the clay mineralogy and organic matter that make up the soil. These 2 factors do not noticeably change in just a few years. On a routine soil analysis, the CEC is calculated from the extractable levels of calcium, magnesium, potassium, and hydrogen. Calcium and magnesium are generally the greatest contributors to the CEC. Unless extremely high rates of lime or gypsum have been applied, these 2 nutrient levels generally stay consistent resulting in a consistent CEC calculation.

Surprisingly, one of the numbers on your soil test that should not drastically change from sampling one sampling event to the next is phosphorus (P). Assuming your soil test P is at an agronomically desirable level, a high yielding corn or soybean crop are not likely to lower your soil test level more than 4 or 5 ppm in a single growing season. If the soil test P level changes more than 10—15 ppm between routine sampling events, it may be the result of inconsistent soil sampling procedure.

To truly compare soil test results from one sampling to the next, it is critical to minimize the variability. To do so soil needs to be sampled to the same depth, following the same crop, at the same time of year, and consist of at least 8 cores.

If you have any questions regarding irregular soil test results, please contact your ALGL agronomist.

Fertilizers and Plant “Availability”

Over the last few months, the ALGL agronomy staff have received many questions regarding different fertilizer products and whether the nutrients are plant available or how long it takes them to “release” the nutrients. The simple answer is that most fertilizer products are highly water soluble, and once they dissolve, the nutrients are in a plant-available form. However, this does not necessarily mean that the nutrients will be taken up by the plants right away. Below we will discuss the potential fate of the nutrients in a few common fertilizer materials if it is not taken up by the plant.

Most questions regarding nutrient availability are concerning phosphorus (P), MAP and DAP. Both products are more than 90% water soluble and are immediately in a plant available if there is adequate soil moisture. However, the P must be near an actively growing plant root to be taken up. So, what happens to the rest of the P if it is not taken up immediately? Much of the applied P will be loosely bound to the clay minerals through a process called adsorption. This fraction of the P can be released back to the soil solution as P concentrations are reduced through plant uptake. However different soil types can bind the P more tightly than others. Soils that are likely to bind P rendering it unavailable are soils with high clay content, high pH, and low soil test P.

Potassium (K) fertilizers such as potassium chloride and potassium sulfate also dissolve rapidly into the soil solution and are immediately in a plant available form that can be utilized by actively growing plants. A portion of the K will be held by the cation exchange capacity (CEC) of the soil and will be released as the K dissolved in the soil solution becomes depleted. The potential exists for the K to be lost to leaching or runoff if the K was applied in excess of the soils capacity to hold it or if there is no actively growing crop to utilize it. Soils most prone to K losses are high sand/low clay content soils, and soils with high organic matter.

The two most common dry nitrogen (N) fertilizers are ammonium sulfate and urea. Ammonium sulfate delivers nitrogen in a form that is immediately plant available. Since ammonium has a positive charge and can be held by the soils CEC, just like K, ammonium is generally considered the more stable form of plant available N. Urea, though it dissolves rapidly, is not in a plant available form initially. Urea requires an enzymatic reaction with urease to become ammonia, which quickly converts to ammonium to become plant available. If the N stays in the ammonium form, losses of N are minimized. Nitrogen losses occur when soils are warm enough for microbial activity to start converting the ammonium to nitrate. While nitrate is also plant available, it is a negatively charged so it is prone to leaching as it is repelled by the soil CEC.

The bottom line is that the best way to ensure adequate nutrient availability for your crops is to maintain good soil test nutrient levels and a desirable pH for and follow the 4R’s of nutrient management. Application of nutrients just prior to crop uptake reduces the potential for nutrient tie up and possible loss. If you have any questions about your specific crop and fertilizer situation, contact your ALGL agronomist.