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Agronomic Support - Table Of Contents The following information gives an overview of micronutrients and their role in a plant’s development. Plant Nutrition Overview Gives a brief description of the "Law of the Limiting Nutrient", as well as the value of soil and tissue testing, and factors affecting nutrient availability. How Elements are Classified Overview of Primary, Secondary and Micronutrients Nutrient Antagonism & Interactions A chart outlining which nutrients interact with, and sometimes antagonize other nutrients Nutrient Mobility Charts showing nutrients mobility in both the soil and the plant Soil Test Trends Charts showing zinc and copper soil test results from 1987-1998 Soil and Tissue Analysis A comparison of the advantages and disadvantages of each analysis tool Crop Response to Micronutrients A table showing various crops, and their level of response to micronutrients Plant Nutrient Requirements A table listing each nutrients role in the plant and common deficiency symptoms and causes Sodium’s Association with Salt Problems A brief description of sodium’s association with salt problems, with some information on how to correct this problem Calcium Sulfate and Gypsum An overview of how to use calcium sulfate to correct nutrient problems How Plants Absorb Nutrients An overview of the three ways plants absorb nutrients Root Absorption of Nutrients Maximum distance of root absorption by nutrient Types of Products – Soil Applied A description of granular (sulfates, chelates and oxysulfates), liquid (EDTA Chelates and Wolf Trax DDP), fertilizer coating and impregnating Chelating Agents A listing of different chelating agents Types of Products – Foliar Applied A description of sequestered, liquid suspension and Wolf Trax Dual Action DDPs Foliar Application Notes Tips for foliar applications Foliar Application vs. Soil Application A comparison list of the advantages and disadvantages of each application Reasons for Nutrient Deficiencies A listing of common reasons for deficiency, by nutrient Amount of Nutrients Removed The amount of nutrients removed from the soil by a crop PLANT NUTRITION OVERVIEW Law Of The Limiting Yield and crop production is limited by the essential element present in the least amount. If you are trying to produce 50 bushels of canola and have fertilized accordingly (with the levels of N, P, K & S required), and an element such as Boron is available only at levels to produce 25 bushels of canola, the most canola you could hope to produce without adding boron would be 25 bushels. There are 16 elements required to produce crops. Without balanced, timely nutrient applications we may encounter symptoms of hidden hunger, which limit yield and quality potential. Over the years we have increased the need for additional nutrients by increasing yield expectations and depleting the natural fertility base through crop production, leaching, cultural practices and the addition of only certain nutrients versus balanced fertility programs.
Identifying Potential Deficiencies Visual symptoms vary between crops and nutrients, but if you can actually see symptoms it is too late to achieve maximum yield. A better approach is to test soil and plant tissue to determine specifically what nutrients may or may not be required and what amount needs to be applied. Remember that micronutrients are called micro because plants require only small amounts. Too much of these nutrients can be as detrimental as too little, or simply put you can pay to decrease yields if an application is not required.
Tissue And Soil Testing Soil testing has been a common practice for a number of years, however only recently have producers began to test for all nutrients rather than only N, P, K. This has led to the development of regional nutrient profiles to help determine the likelihood of nutrient deficiencies in specific geographic regions. The best way to analyze your local conditions remains to keep records of your own operation and over time develop your own data for your specific area. We have recently begun to utilize another tool at our disposal, tissue tests. In conjunction with soil tests they provide valuable information to maximize crop production and target inputs. Tissue tests allow us to determine what nutrients a plant can utilize from the soil, soil tests tell us what nutrients are present in the soil. The difference is that a tissue test will help determine nutrient levels that are plant available at distinct points in time. They discount soil tie-up and climatic conditions that soil tests do not. Used in conjunction with soil tests they are valuable not only for this year’s production but also in developing nutrient profiles of fields and regions.
Factors Affecting Nutrient Availability Soil pH: Soils with pH levels between 6.0 and 7.0 have the best nutrient availability. As levels increase or decrease from this level availability is reduced. Organic Matter: Generally speaking as organic matter increases so does the potential availability of micronutrients, however organic matter may also complex (bind) nutrients limiting their availability to plants. Soil Texture: Sandy, coarse soils have less capacity to hold nutrients than fine textured soils. Fine textured soils tend to bind nutrients in forms not available to plants. Loam, clay loam and clay soils have the least deficiencies. Climate: Extremes of moisture will accentuate deficiencies. Excess moisture enhances yield potential and leaching of some nutrients. Dry conditions discourage root activity at shallow levels and reduce the breakdown and flow of nutrients to the plant. Cool temperatures reduce uptake of nutrients by slowing breakdown into plant available forms and decreasing root activity. *(e.g. phosphate has been estimated to be 3 times more available at soil temperatures of 21 degrees C versus 13 degrees C, boron deficiencies tend to be greatest under cloudy cool conditions) Nutrient Interactions: Soil chemistry is complex and the addition of nutrients is affected by existing nutrient levels as well as the nutrients that we are adding. For instance, high phosphate levels may reduce zinc uptake, the addition of nitrogen can accentuate copper deficiencies, high calcium levels can decrease boron and iron uptake and copper will influence iron. These interactions are the main reason for tissue testing to determine plant availability. Note: These are intended only as a guideline. Nutrients vary region-to-region and field-to-field. Soil and tissue tests are recommended to determine specific nutrient requirements.
HOW ELEMENTS ARE CLASSIFIED Essential nutrient elements are classified into three groups based on approximate relative amounts required by crops. It is important to understand the main benefits these nutrients offer, how they interact with one another and what happens if plants are forced to do without. Naturally, the performance of nutrients on specific crops in specific growing conditions may vary.
Current Practices Have Removed NPKS (Nitrogen, Phosphate, Potassium And Sulfur) As Limiting Factors: For years the main emphasis has been on nitrogen, phosphate, potassium and sulfur, without the addition of micronutrients to the soil. Fertilizers Have Been Refined: As recently as 30 years ago, many of the NPK fertilizers contained micronutrients as impurities. Technological advances in purifying fertilizer have resulted in their removal from NPK. Better Varieties Have Increased Yield Expectations: As varieties yield potential improves, the "Law of the Limiting" rule becomes more important New Crops: Each crop grown requires a different balance of nutrients. As growers introduce new crops to their rotations, they may also increase the need for micronutrients in their soils. Processors Quality Demands: A properly balanced nutrient profile will help increase the quality of your crop, thus making it easier to meet the higher demands made by processors and end-users. More Research: An increasing body of research is justifying the need for balancing all nutrients available to your crop, both macro and micro. It is also giving producers a better understanding of when the crop needs the nutrients within its growth cycle.
FACTORS AFFECTING AVAILABILITY Crop Removal: Greater crop removal also means greater nutrient removal. Leaching From Sandy Soils: Nitrogen, sulfur, chlorine and boron are subject to leaching. Naturally High Ph Soils: Generally speaking, major nutrients are more available at neutral pH (about 7.0), micros at an acidic pH (pH 6.0 to 6.5). Additions Of High Rates Of Phosphorus: Many soil reactions occur with phosphates. Some reduce the availability of other nutrients such as Zn, Cu, Fe. Soil Compaction: Highly compacted soils can limit the amount of water and air available, which are key requirements for nutrient breakdown into plant available form. Cool, Wet Growing Conditions: Increased soil temperatures increase nutrient availability. Tie-Up By The Soil: Common for most nutrients at high soil pH. Use Of Sensitive Crops: Different crops have different nutrient requirements. High Performance Varieties: High performance varieties also increase the plants demand for nutrients. Manure Applications: May tie up nutrients in the short-term due to chemical reactions in manure breakdown.
pH AND SOIL TYPE The Impact of pH and Soil Type on Nutrient Availability The following table shows what nutrients could be a problem for each soil type. However, deficiencies can occur in any situation, so soil and tissue analysis should still be used to identify nutrient deficiencies.
NUTRIENT ANTAGONISM AND INTERACTIONS
NUTRIENT MOBILITY
Mobile In Soil: Nutrients remain in soil solution. This means greater availability to plant. Immobile In Soil: means nutrients will not move with the soil solution and availability is lower.
SOIL TEST TRENDS The following two charts reinforce the need for a balanced fertility program. The most likely causes of these trends are depletion of natural fertility base through crop production, leaching, cultural practices and the addition of only macronutrients.
Soil Analysis vs. Tissue Analysis Both provide useful information for this year’s crop production, as well as data that will be useful for future planning. In short, soil analysis provides us with a picture of the nutrients present in the soil. Tissue analysis provides us with the nutrients available to the plant.
Combined Provide a nutrient profile of each field that is useful in planning crop rotations and specific fertility requirements. This allows for targeting nutrients in a precise manner on a yearly basis. Example: Field analysis history indicates that there is a problem with available zinc. Crop plan is for beans (which respond to zinc). Fertility plan incorporates a zinc application.
CROP RESPONSE TO MICRONUTRIENTS Crops vary in their response to application of a given micronutrient. The following ratings are offered as guides to such response when the level of one or more of these nutrients is low or deficient in the soil.
PLANT NUTRIENT REQUIREMENTS BY ELEMENT
SODIUM'S ASSOCIATION WITH SALT PROBLEMS The sodium tends to displace the other cations on the exchange complex, to accumulate in the soil solution, and to interfere internally with the plant physiology. Sodium may exist in the soil either as a free salt or as part of the exchange complex. Free sodium will leach readily, while exchangeable (absorbed) sodium can be removed from the exchange complex by replacing it with another cation. When the use of gypsum or sulfur containing materials is warranted, fineness of grind, mixing thoroughly in the soil as deep as practical, and use of good quality water are important considerations.
All soil amendments should be well mixed into the soil and water applied soon afterwards to start reclamation. The approximate amount of water that must pass through the root zone to reclaim a salt affected soil can be estimated from the following information. 6 inches of water per foot of root zone will remove 50%
Gypsum (calcium sulfate) contains 20-25% calcium and 15-20% sulfur. It is used to supply calcium and sulfur to the plant without affecting the pH of the soil. Gypsum will help correct high magnesium and sodium content in soils by forming water soluble compounds which are leached out of the soil profile. Sulfur will react with magnesium and calcium with sodium. Gypsum will help loosen tight clay soils. It is a particularly effective way to correct calcium deficiencies in high pH and/or alkaline soils. For maximum crop production and quality, it is generally recommended that the base saturation level of calcium be in the 65-80% range. Gypsum is produced by mines and as an industrial by-product. It is usually best to use the mined gypsum as the other may contain heavy metals and other contaminants. Gypsum will react faster than elemental sulfur both as a soil additive and also in releasing nutrients to the plant. It provides two essential nutrients versus only one and thus will react with sodium as well as magnesium. Of all calcium compounds, gypsum (CaSO4 ) is considered the most soluble and cost effective for soil reclamation. Elemental sulfur is considered the slowest acting of all soil amendments. Products that contain a variance of granule sizes are considered the best due to the natural "time release" of the particles as they are broken down. Gypsum is most effective when broadcast and allowed to leach through the soil profile but also works well with a shallow incorporation. Some producers apply a seed row application as a source of calcium and sulfur. This works well in soils that are in relatively good shape. If the soil has a sodium or magnesium excess, however, rates need to be increased and the product needs to be broadcast. Calcium acts as a catalyst for nitrogen uptake and by reducing magnesium levels, phosphate in the soil tends to become more available. Sources: Fertilizers and Soil Amendments Prentice Hall International 1981
Mass Flow: Mass flow is the movement of soil, water and nutrients in solution to the root. This takes place with nutrients that are mobile in the soil or when nutrients are chelated or complexed. Diffusion: Diffusion is the movement of ions from a higher concentration of soil to a lower one. This is related to nutrients that are in solution. As roots remove nutrients from the soil, the soil around the extraction point will contain a lower concentration of nutrients. Diffusion moves nutrients back into the area of less concentration. Root Interception: Root interception means the root actually runs into the nutrient. The root system only comes in contact with about 1-4% of the soil surface area. Nutrients that do not remain in solution are picked up by root interception. Nutrients applied in high amounts (such as phosphate) provide lots of area for the root to "hit." Those applied in minimum amounts (most micronutrients) are not present in high enough concentrations to supply adequate amounts for the crop.
Plants can only absorb nutrients from a limited soil volume surrounding the roots. This soil volume is different for each nutrient.
Therefore the amounts of available nutrients are directly related to root development (number and length). SOURCE: AGPM (Maize) Research Centre, France
SOIL APPLIED PRODUCTS There are numerous soil applied products available for producers to utilize. They all have advantages and disadvantages. Following is a listing and brief discussion of the most common formulations. Prior to using these products, it is always prudent to ask for the product specification sheet, taking care to note solubility factors as well as heavy metal contents. Remember that these nutrients come in many different forms and may contain various byproducts that may or may not be beneficial. It is also useful to note that it is tough to make a straight pound for pound comparison when dealing with different forms and formulations of these products, since efficiency ratios must also be taken into account.
GRANULARS Granular micronutrients are normally blended in with the macronutrient fertilizer granules.
Sulfates Products are in plant available sulfate forms. Advantages: Over Oxysulfates – Tend to have higher analysis (higher concentration) and higher availability, thus you have to handle less product. Good nutrient availability at the beginning of the season. Disadvantages: Over Oxysulfates – Less product put on field, therefore distribution of granules and seed/granule contact may be reduced. Availability will be reduced due to product being tied up or leached, depending on your soil structure. Climate and soil structure are the biggest factors in determining the rate and speed of nutrient tie-ups. It is important to ask for product specification sheets to determine solubility and heavy metal content. Copper products tend to be in the 25% analysis range, zinc and manganese over 30%.
Chelates/Complexes/Sequestered Products usually consist of a base nutrient treated with chelating agents. Advantages: The chelating agent keeps nutrients in plant available form longer, which reduces the effect of soil tie-ups and degradation. This means that you get both immediate plant availability and extended sustained feeding due to the increased plant availability. Utilize 7:1 efficiency ratios (7 times more efficient than non-chelated forms), meaning that a 10% product should be treated as 70%. Formulated to have a density similar to fertilizer (typically less than sulfate and oxysulfate products), which reduces settling out problems and increases the amount of product required in blends. This helps with distribution of the granules and seed/granule contact. Disadvantages: The addition of the chelating agent will add to the cost of the product (this is usually made up for in the increased efficiency). Numerous chelating agents are used in this process (click here to see a full list of chelating agents). It is prudent to request manufacturers specification sheets on these products. Chelated products usually range from 5-10% in analysis.
Oxysulfates Oxide based products that are mixed with other materials to reduce product analysis. Advantages: Micronutrients are initially released to the soil environment in the oxide form and are available to the plant through root contact. This reduces losses by leaching during heavy rainfall or in irrigated lands. Over time, formulation may break down into plant available forms (although they are also susceptible to tie-up in the soil). Ease of handling in blends (due to high analysis products and the ability to blend two products at once) and competitive pricing. Disadvantages: Oxide form has low water solubility, and thus is not readily plant available. Root interception of insoluble elements is estimated to provide less than 5% of plant uptake needs. Have a fit for a long-term strategy, but generally need to be used in conjunction with other products (ie. foliar applications) to overcome their availability problems. Soil test will confirm the soil building properties of these products, but tissue tests are a better measure of efficiency since they benchmark what nutrients are in plant available forms versus stagnant in the soil. Care should also be taken when ordering these formulations to determine the presence and level of heavy metals. Most of these products have an analysis in the 20% range.
LIQUIDS EDTA Chelates Advantages and disadvantages of the EDTA chelated formulations are similar to that of the granule Chelates/Complexes.
There really is no comparison between Wolf Trax DDP Dual Action Micronutrient technology, and the traditional granular micronutrient products. The unique formulation process used by Wolf Trax to manufacture DDP Micronutrients ensures that, when blended with granular fertilizer, the DDP will be evenly distributed, and thoroughly coat all the prills in a batch of fertilizer. Throughout the blending process right to application in the soil, DDP products stay coated on the prills. This provides a new way of delivering micronutrients to the plant, ensuring more even distribution throughout the root zone, and superior application. Advantages: Superior distribution - When applied as a coating on granular, prilled fertilizer, Wolf Trax DDP Micronutrients are available to the crop the instant the crop accesses the nitrogen, phosphorus and potassium fertilizer. High analysis product therefore less handling and more price competitive. Quality standards keep the amount of undesirable heavy metal and other contaminants well below industry standards. (Unmatched quality) Powder greatly reduces the volume of product handled, thus decreasing the shipping and handling costs. Powder formulated using innovative new technology not currently available in any other dry micronutrient product. More convenient to handle, with an indefinite shelf life and no need for heated storage. Increased product distribution, since each macro fertilizer granule will have a small amount of micronutrient on it. Disadvantage: No soil building capability. Low concentration of micronutrient provides for efficient use of nutrient in year of application only.
IMPREGNATING This may be done with liquid suspension products. Advantages: Liquid products tend to have a high analysis (highly concentrated) and therefore require low rates. There’s a benefit for product distribution, since each fertilizer granule will have a small amount of micronutrient on it. Disadvantages: Low concentration of the micronutrient in the fertilizer granules due to the low rates required. Possibility of tie-up with other nutrients (ie. zinc in direct contact with phosphate). No soil building capability. Generally speaking, as long as you’re willing to accept that this application will provide enough nutrition to spoon-feed your crop for a year without any soil building capabilities, this is an alternative. A mid-season tissue test is still recommended in areas that have shown marked deficiencies in previous years. Analysis of these products ranges upwards of 20%.
CHELATING AGENTS Definition Chelating agents alter the electronic charge from + to – preventing nutrients from being precipitated out by phosphates, carbonates and other soil and fertilizer components. This is done prior to the addition to the soil and protects the nutrient from being tied-up.
Application Ratios The strongest chelating agents are the ethylene diamine tetra acetate (EDTA) family. They are synthetic not organic. Since they are stronger than the organics, they are used at a ratio of 10 to 1 compared to the intermediates, which are used at 7 to 1.
FOLIAR APPLIED PRODUCTS As with soil-applied products, there are numerous foliar applied products to choose from as well. The key when looking at foliar applied products is the timing of application, and the plants corresponding need of that micronutrient. Most foliar applied products provide either a short-term boost or a long-term slow release of micronutrient to the plant. The only exception is Wolf Trax Dual Action formulations, which provide both these traits.
Sequestered Products Contain complexing agents that make these products readily plant available. Advantages: Provide quick plant uptake (usually within 48 hours) over a short time period. Utilize a 7:1 efficiency ratio (they are 7 times as efficient as soil applied products due to coverage and uptake). Disadvantages: Does not provide any sustained feeding. Low analysis equates to high rates.
Liquid Suspensions Produced utilizing oxide or oxychloride bases. Advantages: Provides sustained feeding over time (up to 3 weeks). Products are high analysis, which allows for low rates. Flexible because they can be used with liquid fertilizers, impregnation and as foliars. Disadvantages: Has a delayed uptake, therefore limiting timing of application. Tendency of formulation to settle out.
Wolf Trax DDP (Dry Dispersible Powder) Unique Dual Action formulation combines the immediate availability of sequestered products with the extended availability of suspension products. Only Wolf Trax micronutrients provide immediate plant uptake (within 48 hours) together with continuous feeding over time. Advantages: Powder formulated using innovative new technology not currently available in any other dry micronutrient product. Provides the rapid availability of sequestered products with the sustained release features of suspension products (providing plants nutrition within 48 hours and lasting up to 28 days after application). This allows producers the flexibility to tank-mix with existing passes without missing important development stages in the plant. Designed to disperse almost instantly in water and stay in suspension (doesn’t settle out under agitation). Quality standards keep the amount of undesirable heavy metal and other contaminants well below industry standards. Products are high analysis, which allows for low rates thus reducing handling and storage. Flexible because they can be used with liquid fertilizers, coated onto fertilizer, as a foliar or a seed treatment. Disadvantages: None when used as a foliar.
Properly Timed Foliar Applications:
Ideal Conditions Favoring Nutrient Uptake:
– During critical stage of growth – times of high nutrient demand (vegetative to reproductive) Economic Timing: Foliar applications generally will not provide enough profit to cover the cost of a separate application; therefore they should be applied whenever possible with an existing pass over the field. If there are marked deficiencies showing up on a particular field, an early application, such as with a herbicide, may be required. Recent research has indicated that fungicide timing works just as well. Analysis: One tool that has been overlooked in planning fertility programs is the tissue or petiole analysis. Long a standard in horticultural production producers are now beginning to utilize this practice to help plan fertility programs. Tissue tests determine what a plant is able to take out of a particular soil, versus soil tests that determine nutrient content, but not necessarily availability of these nutrients. Final Considerations: Foliar and micronutrient nutrition are not meant to replace good soil fertility programs but rather to enhance them. They are most attractive to producers looking for the last extra bushels, higher grades or enhanced nutrient uptake and balance. As crop production techniques and new high yielding crops and varieties are introduced, correct and balanced nutrition programs may be the areas where profit and loss are determined. Proper testing and scientific support (i.e. crop responses to specific nutrients) is critical.
FOLIAR APPLICATIONS VS. SOIL APPLICATIONS There are advantages and disadvantages to both of these techniques; the following is a brief summary of the benefits and limitations of each system.
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