Phosphorus (P) is a key nutrient for crop production, and keeping adequate levels of P in the soil is important for maximizing plant growth and development. However, understanding the various analytical methods for determining soil phosphorus can be challenging. The greatest confusion often lies in understanding why there are different analytical methods for determining soil P. The key to understanding this is to differentiate between total, available, and extractable levels of a soil nutrient.
Total P is the total amount of phosphorus in the soil. This can be P contained in organic materials, P in soil solution, exchangeable P, and P contained in insoluble mineral forms, and can be quite high in many soils. This information generally has limited agronomic use, however, because the amount of P that is actually plant available is generally only a small amount of the total P in the soil.
Of much greater benefit from an agricultural perspective is what is referred to as extractable P. Extractable P is the amount of phosphorus that can be extracted, or removed, from the soil by using one of a number of different types of chemical extractants. These extractants have been developed to remove certain forms of P from the soil, and this can be a more accurate index of what might be actually available to a growing crop The ultimate goal of an extractant is to reliably and consistently determine levels of the nutrient that correlate with the amount of that nutrient that might be available to a growing plant.
Bray-Kurtz P1 (Bray P1) has long been utilized in the Great Lakes region as the “standard” P extractant. It was developed in 1945 at the University of Illinois to correlate with the plant-available P fraction of the soil in slightly acid soils. Many of the P recommendation models, including the Tri State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa, still utilize Bray P1 soil test values in their equations due to the widespread use of the extractant when these models were developed.
Bray P2, or strong Bray, is a more acidic solution that extracts forms of P that are less soluble than those extracted by the Bray P1 method. This extractant was commonly used when rock phosphate was the major P fertilizer product used in agriculture. It is still utilized by many to measure less soluble forms of P, what is commonly referred to as “active reserve” P in the soil, although most P recommendation models do not consider Bray P2.
Olsen P, or bicarbonate P, is a procedure that was developed in the 1950’s for determining P levels in neutral to alkaline soils. These soils are more commonly found in areas west of the Great Lakes region, so this test is only performed by request.
Mehlich-3 is the most commonly used extractant currently employed by soil testing laboratories in the region. It is a relatively safe extractant to work with and can be used to determine levels of other nutrients in addition to P, which makes it a more efficient method than others. Mehlich-3 is effective on the same types of soils as the Bray P1, but Mehlich-3 soil test P values are somewhat higher than those obtained by a Bray P1 extraction. However, the Mehlich-3 values correlate well with Bray P1 values, so Mehlich-3 values can be regressed into a Bray P1 equivalent number by using a mathematical operation. This allows soil test P values to be reported as a Bray P1 equivalent, which is necessary for making P fertilizer recommendations.
For any type of laboratory analysis to be useful, interpretations must exist in order for the data to be utilized to make decisions on a field scale. While different extracts have been developed to target different forms of P in the soil that may be plant available, this does not mean that the values determined by an extraction are absolute quantities of that nutrient in the soil. Much research has been done to correlate these soil test levels with crop response to a fertilizer material, and it is that correlation that is necessary for interpreting this information and making decisions.
It's almost the deadline to submit a picture for our 2019 A&L Great Lakes calendar! We want to see pictures that illustrate what fuels your passion for agriculture and customer service. When you get that picture captured, send it to email@example.com along with your name and address. Please submit your pictures in the highest resolution possible before August 1st, 2018. In August we will select our favorite pictures, then we will be letting our followers on Facebook vote on their favorite, to be on the cover of the 2019 calendar. Follow us on Facebook for voting details.
The 2017 Purdue Precision Dealer Survey shares some interesting insight into the adoption of precision soil fertility management. Over 80% of ag dealers offer services like precision soil sampling and variable rate nutrient application. More recent practices such as satellite/aerial imagery are also gaining popularity, with about half of dealers providing these services.
The adoption of precision ag started in the mid 90’s, and it continues to grow, although not as rapidly as expected. Access to these services is not a limiting factor, but adoption still lags. As estimated by dealers in 2017, only 43% of producers are utilizing precision soil sampling, and only 38% are making variable rate applications. This means 5% of growers are spending money on the collection of spatially referenced soil samples and not gaining the benefit of variable rate application of fertilizer inputs.
Looking into the future of precision fertility management, there is tremendous potential and a significant amount of work to be done. These are just a few of the interesting facts contained within the Purdue survey data. To dig into the survey data for yourself, see the full report at http://agribusiness.purdue.edu/files/file/croplife-purdue-2017-precision-dealer-survey-report.pdf .
Both soil-applied and foliar-applied nutrients have a place in modern agricultural production systems. Historically, the vast majority of nutrients were applied to the soil, either as manure or some other type of organic material, or as synthetic fertilizer materials. This method has a number of distinct advantages.
Perhaps the most significant advantage of soil-applied nutrients is that this method supplies nutrients where the plants are designed to take in nutrients: at the roots. The roots of higher plants are adapted to take in nutrients and water from the soil and distribute them throughout the plant through the plant’s conductive tissues. Conversely, plant leaves are more adapted to keeping materials out of the plant due to their structure and composition since few nutrients are taken into plants via the leaves in a natural system. Because of this, plant roots can assimilate more nutrients into the plant than can the leaves of a plant.
However, foliar-applied nutrients also have a number of distinct advantages over soil-applied nutrients. One of the most significant of these is the rapid intake of nutrients. Because these materials are applied directly to the plant rather than the soil, their intake is not dependent on the nutrient moving through the soil and into the root. Therefore, they can have an immediate impact on the plant, which is critical when a given nutrient is lacking. Most modern foliar fertilizers have been formulated to ensure quick penetration into the plant, which can speed this process even further.
Another major benefit of foliar-applied nutrients is the fact that these nutrients bypass the soil altogether. Soil fertility is more complicated than the simple presence or absence of an element in the soil. For that element to be assimilated by the plant, it must be in a form that the plant can take up. Often a potential plant nutrient may be present in the soil, but certain soil conditions, such as pH, may cause that nutrient to be held in a form that cannot be taken up by the plant. If more nutrient is applied to the soil, it still may not benefit the plant because the underlying reason for the deficiency still exists. In these situations, foliar applications of nutrients may be the most effective way of supplying the needed nutrient to the plant.
Modern agronomic production is very sophisticated and requires a number of different techniques to meet the nutrient needs of the crop. Therefore, the best approach is to fully assess the situation to determine the best application method. Both application methods have distinct benefits and should be a part of the plant nutrient toolbox.
Soil quality, often referred to as soil health, is a topic that continues to receive much attention. As producers continue to push for greater yields and improved economics in their crop production system, more emphasis is being placed on the soil environment and its ability to produce a healthy crop in a sustainable way. However, evaluating soil quality is not always as simple as pulling a soil sample and sending it to the lab.
The USDA-NRCS defines soil quality as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans”. As evidenced by this definition, there is no one set parameter by which one measures soil quality. The term can be interpreted in a number of ways depending on the situation. Different soils in different locations will have different forms of “quality”, so the producer must learn to understand the capabilities of their soil and temper their expectations according to that capability.
One of the most fundamental steps to take when evaluating and managing for soil quality is to understand the soil that you are working with. Some properties of the soil cannot be practically changed. These properties, known as inherent soil properties, are a result of how the soil was formed. One example of this is soil texture. A sandy soil will, for all practical purposes, always be a sandy soil. Short of incorporating a huge amount of silt or clay, there is nothing you can do to change this. Massive changes like this can also result in negative impacts on the soil. However, there are other soil properties that can be influenced somewhat by management. These properties, known as dynamic soil properties, can be influenced by how the soil is managed. For example, soil organic matter content is a dynamic soil property. It can change, however slowly, by how you manage tillage and crop residues. Soil structure can also be improved through proper soil management, again these changes take years to have a significant positive impact.
A number of different assessments should be made, including a thorough examination of the physical properties of the soil. While soil health testing methods are being developed, these are not standardized today and interpretation of results still require validation. In addition, a standard soil test is also an important way to evaluate the chemical properties of the soil to ensure that nutrient levels are appropriate for growth.
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 most 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.
Meet Kelsey Roth, A&L Great Lakes Labs' new receptionist and customer service specialist. She began her tenure with ALGL in early March 2018, but has worked in customer service for several years. Kelsey has a vital role within the company because she will often be the first person that our customers interact with, whether on the phone or when they come through the front door. She looks forward to working with and getting to know all of our customers.
In her spare time, Kelsey loves to golf, read, and spend time with her cat Wesley (he likes to go on walks outside). Kelsey is a native of Decatur, Indiana and went to Ball State University in Muncie, Indiana, where she majored in psychology. Welcome to the A&L Great Lakes team, Kelsey!
Not that long ago, creeks, rivers, and ponds were an acceptable source of spray water. This practice seems unthinkable today, given our understanding that products like glyphosate are rendered inactive by clay particles and other impurities in the water. Through research it has been demonstrated that most pesticide chemistries are impacted, often negatively, by the various dissolved minerals and pH of the water used as the carrier.
Weed resistance, rising input costs, the need for effective cover crop kills, increased use of companion products such as foliar fertilizers, along with an increase in spray solution modifying adjuvants reaching the market have increased the need to quantify the quality of water used for pesticide dilution. Currently it is more common to analyze spray water quality after something has gone wrong rather than proactively testing to identify potential problems.
The stability of pesticides in the spray tank is often directly tied to the pH and the presence of dissolved minerals in the spray water. Depending on the pesticide chemical formulation, the active ingredient can be rendered inactive by either reacting with hydroxyl groups at high pH or with additional hydrogen ions at low pH. These chemical alterations of the active ingredient can also drive chemical reactions with the dissolved solids in the water rendering the pesticide inactive.
Herbicide products like dicamba and 2-4,D amine can be unstable at pH’s above 7.0. Insecticides and fungicides are even more sensitive to spray water pH. For example, some can be stable in the spray tank for days to months at a water pH of around 5, while at a pH of 9.0 are stable for only minutes. Many of your brand name pesticides that are pH sensitive are buffered in the formulation; however, this is not the case for all generics. Adjuvant manufactures have been addressing this need with a wide array of spray water modifiers to buffer pH concerns and tie up dissolved minerals before they impact the pesticide performance.
Analysis of your spray water will greatly improve the success in identifying the right adjuvant and using the product at the correct rate. The use of ammonium sulfate (AMS) with glyphosate applications is a good example of this. When spraying glyphosate, the label rate for AMS is 8.5 to 17 pounds per 100 gallon of spray water. By testing your spray water, you can pinpoint the rate needed for the application, possibly saving on the cost of excessive AMS while still ensuring adequate product to protect the efficacy of the glyphosate. If you are interested in seeing where your spray water stands, please contact the lab for sampling kits and for more information.
Quality pasture is one of the greatest assets in the production of ruminant livestock. Good pasture provides high quality feed very cost effectively and with a relatively low labor requirement. However, many pastures receive little if any management; resulting in low yielding, low quality feed. Here are a few basic tips when it comes to managing for a quality pasture.
Forages are unique plants that require careful management to perform to their fullest potential, which in turn can have major benefits to animal productivity.
In 2015, the International Plant Nutrition Institute (IPNI) released their report on soil test levels. Potassium was one of the soil nutrients that were exhibiting a steady decline in soil test levels. A&L Great Lakes Laboratories regularly contributes to the IPNI data set, and we also analyze our data for the Eastern Corn Belt region.
In the graph above the green bars indicate the average potassium soil test levels in ppm. The dashed line is the trend line of the soil test values, indicating an average 1.3 ppm per year decline. In addition, the blue line on the graph indicates the percentage of samples that are likely deficient. This trendline is of particular concern since it exhibits a steady increase in the percentage of soils which are likely deficient in soil test K levels.
While it is difficult to attribute these declines to only one factor, yield and fertilizer application trends show an overall net negative balance. On average, potassium is being removed from the soil faster than it is being supplied. It takes, on average, the addition of 8 pounds of K2O raise a soil test by 1 ppm. Inversely, the removal of 8 pounds of K2O lower a soil test by 1 ppm. On an annual average, crop removal of K2O exceeds application by 10 pounds per acre per year. Looking at USDA data, the crop removal of potassium at USDA average yields for corn and soybeans began outpacing average potash applications in the late 1990’s, just before the steady increase of deficient soils begin in the early 2000’s.
There are many factors that may potentially contribute to these trends. Better crop management practices and improved genetics are leading to rapid increases in yields. If those higher yields are not accounted for when generating fertilizer recommendations, particularly if actual yields exceeded yield goals, nutrient recommendations may be inadequate to supplant what the crop actually removed. Predicting future yields in these high yield environments can be difficult, so it may be more beneficial to base crop removal on yields obtained in previous years, and to adjust future removals to accommodate high yielding crops that occurred since the previous fertilizer application.
Another factor may be the financial, logistical, and equipment limitations brought about by the high amounts of fertilizer material which are required to meet these higher crop removal needs. As an example, if applying nutrients in the form of MAP (11-52-0) and potash (0-0-60) on a two-year application cycle to replace the nutrients removed from a 240 bushel corn crop and a 70 bushel soybean crop, a total of 500 pounds of fertilizer per acre would be required. If an application is capped below this level due to fertilizer budgets, equipment limitations, or concerns of overloading the soil’s ability to retain nutrients, applications adequate to meet crop removal may not be made. Often these maximums are in the range of 400 to 500 pounds, not covering crop removal in some yield environments.
A final management practice that may be reducing the amount of potassium held by the soil is the application of high calcium products at the same time as potassium applications. The soil cation exchange capacity (CEC) has a limited ability to hold cation nutrients, and if a large quantity of calcium is added to the system, it can lead to losses of soil potassium. This is amplified when multiyear applications of potassium are made, or when large applications of calcium products are made in a similar time frame as a potassium application.