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Plant Nutrition - Potassium

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Potassium in Plants and Soils.

The Importance of Potassium

photo.jpg CropNutrition - The Importance of Potassium

 

Potassium (K) is an essential nutrient for plant growth and is classified as a macro-nutrient due to significant amounts of K being taken up by plants during their life cycle.  This compilation is designed to instill the basic understanding of potassium (K) nutrition of plants, how it reacts in soils, and what it dows for the plants, and how it effects efficient crop production and quality.

  • Not all plants uptake the same amount of potassium such as corn silage and alfalfa will uptake and remove from the soil far greater amounts of potassium than say grain crops.  Understanding this aspect is vital as to better design a nutrient plan for crops but this is largely true of all macro-nutrients and crop types.
  • Depending on the amount of available K and exchangeable K and your plants needs you may need to add K to your fertilizer nutrient plant.

The total amount of K in soils often exceeds 20,000 ppm (parts per million).  Almost all of this K is held in the structural components of soil minerals and is not available for plant uptake.  Due to the differences in plant/crop type and the effect of weathering of these materials the amount of K supplied by soils varies. Therefore, the need and amounts for K in a fertilizer program varies.

 

The Potassium Cycle

large.potassium-cycle-xlarge.jpg.11b7eb0

 

photo.jpg Univ of Wisconsin Integrated Pest and Crop Management

 

Soil Moisture factors on available K

  • Dry soil or low soil moisture.
    • Approximately 78% of the plants K needs are taken up by the roots.
    • Higher soil K levels relieves some of the nutrient stress associated with drought.
      • K alleviates the effects of both moisture deficit and excess on the crop and counteracts the yield reductions due to either.
    • Low K in the soil can reduce plant uptake of potassium during dry/drought conditions.
  • Soil moisture increased from 10% to 28% can increase potassium uptake by 175%.
    • Too high soil moisture and cold soils will reduce oxygen availability and restrict the uptake of K.  (wet roots)
    • Too high soil moisture can also work to leach away available potassium to the plant.
      • Irrigation can play a role in leaching K in sandy and mucky type of soils.

 

Soil Temperature & PH for Potassium

  • Optimum soil temperature for uptake is 60-80°F.
    • Low temperature will restrict plant growth and the uptake rate of available K.
    • Early planting can reduce the uptake of K.
      • Increasing K may be a viable option.
  • High available K levels will increase K plant uptake at low temperatures.
    • Phosphorous and Potassium are typically high in rooting/starting fertilizers for this reason as together they greatly assist root growth. 
  • Low PH conditions and acidic soils
    • Higher competition for CEC sites at a lower PH.
      • Low ph can be a cause for potassium deficiency in crops while having sufficient K quantities of K in the soil.
  • Correct PH conditions or limed soils.
    • Enables more K to be held in CEC and also reduces leaching.

 

Illustration of K in soil (organic particles are negatively charged.)

large.59c27ce8e13d1_exchangableandsoluti

https://extension.psu.edu/programs/nutrient-management/educational/soil-fertility/managing-potassium-for-crop-production

 

Potassium is held in soils in 3 states; soil solution, exchangeable/fixed, and mineral.

Soil solution - Usable to plants.

  • Potassium (K) is taken up by plant roots only from the soil solution.
  • K in solution is a small fraction of the total K in soil.
  • The soil solution is replenished with K from other sources in the soil to be usable by plants.
  • That replenishment comes primarily from readily available, “exchangeable” K.

 

Exchangeable or Fixed K

  • Exchangeable K, like other positive charged ions such as magnesium (Mg), calcium (Ca), and aluminum (Al), is loosely held in soil by an attraction to the negative charged surfaces of soil particles, this is similar to magnets on a refrigerator.
    • This is not held strongly and can be leached.
  • The amount of exchangeable K in the soil is dependent on the soil's cation exchange capacity or (CEC).
  • When K is added to soil it occupies negative charged sites on soil particles by “kicking off,” or exchanging with, other positive charged ions.
    • The creates a reserve of K in the soil waiting for a place in the soil solution to become available.
    • As plant uptake occurs, K is released from these sites to the soil solution.
    • The amount held in reserve and how much is released in soil solution is directly dependent the proportion of the CEC sites it occupies.
  • The amount of exchangeable K is related to the amount of K available to the crop and the crops uptake.
  • Clay type and Iron levels in the soil affects K availability.
    • As Fe3+ is reduced K can be trapped between clay layers for smectite
    • With illite K will be released.

 

Soil testing for potassium.

  • Soil test measures K in soil solution and exchangeable K.
    • Take soil test at same time each year.
    • Is very important to test annually and regularly for sandy and organic soils due to leaching.
  • When dried the type of clay particles/minerals can affect the amount of K available.
    • Soil heavy in micas release K during freeze and dry cycles at higher rates.
    • Soils with low mica and high quantities of exchangeable K are less affected by freeze thaw. 
  • Time of soil sampling in regards to wet and dry cycles can affect the soil test.
    • Spring, summer, fall and winter will show different levels.
  • The factors of weathering, plant uptake and soil clay and mineral make up are all factors that can alter exchangeable K.
    • It is not advised to input high K on sandy and mucky soils in the fall due to leaching aspects.
      • By spring most will be leached away.

 

Mineral - Not usable and very slowly released

  • The majority of K in soil is held more tightly, trapped, or as part of the structure of soil minerals.
    • approximately 90-98% of total soil K is found in this form.
    • Feldspars and micas are minerals that contain most of the K and plants cannot use the K in this form.
  • These forms, called nonexchangeable K, are generally either unavailable or only slowly available.
    • Not viable to depend on this for plant use.
  • Mineral K is not, typically measured as part of the soil test procedure.
  • Decomposing organic matter in soil contributes little K.
    • K is a soluble nutrient that leaches quickly from fresh crop residue, manure and sandy soils.
    • However organic matter is important to K fertility because it provides many negative charged sites for holding exchangeable soil K.
    • Finding this balance or fertilizing management with the your nutrient plan is vital for healthy plants.

 

Union Break!

photo.jpg Alex Clare - Alex Clare - Open My Eyes

End of Union Break!

 

Potassium in Plant Growth

Potassium directly assist the plant to with stand stressful conditions and builds a stronger resistance to disease and plays a role in nearly every facet of crop production.  Photosynthesis, control of plant N, formation of new proteins and tissues, and strength of cell walls and stalk tissues are all influenced directly by K nutrition. 

  • K is associated with movement of water, nutrients, and carbohydrates in plant tissue.  K is involved with enzyme activation within the plant which affects protein, starch and adenosine triphosphate (ATP) production.
    • The production of (ATP) regulates the rate of photosynthesis.

The main value of K to crop plants is in times of stress.  Full and balanced nutrition in all essential nutrients maintains a plant’s vigor and reduces its vulnerability to stress.

  • Potassium, role in a plant’s defense, which is primarily preventative.
  • Resistance of some varieties to stresses of disease, temperature, or moisture is related to a greater ability to take up soil K.

Plant disease requires at least two conditions

  • An infection point or entrance and a favorable environment for development.
  • Resistance to both the incidence and the severity of disease is conferred by K through alleviating these two conditions.
    • In some plant species, wounds, which are potential entrance sites for infection, heal more rapidly when the plant is supplied with adequate K.
    • Even if higher numbers of disease organisms are present, plants nourished with sufficient K are less affected because of greater plant integrity.
  • Even if disease is able to enter the plant the development of disease in a plant is affected by its K levels.
    • When K is deficient, production of proteins and tissues stops and production materials accumulate, thus providing an ideal environment and food source within the plant for disease to develop.

Potassium also helps to regulate the opening and closing of the stomata which regulates transpiration which is the exchange of water vapor, oxygen, and carbon dioxide.

  • If K is deficient or not supplied in adequate amounts, growth is stunted and yield is reduced.
  • For perennial crops such as alfalfa, potassium has been shown to play a role in stand persistence through the winter.

Other roles of K include:

  • Increased root growth and improves drought resistance
  • Maintains turgor;
    • reduces water loss and wilting
  • Aids in photosynthesis and food formation
  • Reduces respiration, preventing energy losses
  • Enhances translocation of sugars and starch
  • Produces grain rich in starch
  • Increases protein content of plants
  • Builds cellulose and reduces lodging
  • Helps retard crop diseases

 

Potassium Management

In evaluating a fertility program analyzing the K soil test trend over time gives a perspective that is more important than the level at any one given time.  Maintaining the level within the optimum range over time is the goal.

  • The response to added K can also be predicted somewhat by anticipating stresses to the crop.  If the crop is planted in a poorly drained field, or conversely, a drought field, moisture stress is likely, and so is a response to added K if soil levels are even borderline low.

Managing K fertility for a corn grain/alfalfa hay rotation is a matter of extending your perspective from the K requirement of the present crop to the requirement of the next crop as well.

A profitable response to added K is most likely when soil test levels of K are low.  Within the optimum range, nutrient availability will not limit growth.

Soil test levels are thus put into the context of the rotation.  Potassium can be stockpiled during the corn years of a rotation in anticipation of the large requirement by alfalfa later in the rotation.

  • Applying manure to supply nitrogen to corn will likely supply K in excess of what the corn crop generally removes. But because the concentration of K in the soil solution is low, and because it is held by the CEC, there is little potential for this nutrient to be lost through leaching, particularly in heavier soils of high CEC.
  • The little leaching that does occur provides K for subsoil uptake by the deep-rooted alfalfa crop. In this case, soil test K levels may exceed the optimum during the corn years of the rotation, but for the rotation overall they should be around optimum on the average.

 

large.59c2c87d86730_Potassiumsoiltestlev

Potassium soil test levels for corn-alfalfa rotation during which manure was applied in corn years to build up K for hay crop requirements.

 

The need for increasing or reducing potassium in a fertilizer program can be determined by conducting and analyzing plant analysis data and soil testing.

  • Soil testing is the most reliable predictor of this need.

 

Calculations of K2O recommendations for a soil of CEC=10 at three initial soil potash levels and for three crops.

large.59c2c33ccc025_Pottasiumchart.jpg.a

Penn State Extension

 

For most soils, this adequately predicts K availability however in some soils, the mineral K (which is not usually measured) supplies a significant amount of K to the crop, and thus the test based on the exchangeable and solution K does not fit the situation. 

  • This is most likely to occur with soils containing high amounts of the illite and vermiculite types of clays.
    • The clue may be that there is little change in soil test K when K removal is expected to be large, or conversely (because the reaction is reversible), little change in soil test K level when K is added.
    • Once this is a known factor this aspect can be accounted for in your nutrient management plans.
      • This is not a common scenario.

Reduced potassium in soils reasoning over time.

  • Not sufficiently replacing potassium after crop harvest and rotations.
    • Cost of potassium fertilizer.
  • Minerals in soils.
    • Soil minerals in K cannot replenish K to account for plant uptake.
      • Is true for deep rooted plants to bring up K but the amount is not sufficient.

Adjusting K in the soils

  • Soil buffering capacity 
    • Less K is needed to adjust PPM levels.
      • 6 to 7 pounds per acre will adjust 1 PPM.
    • Less time is needed for a change to occur to raise or lower soil k levels.

Crop removal of potassium

  • Alfalfa by the ton K removal 180 lbs
  • Corn silage by the ton K removal 160 lbs 
  • corn grain by the bushel K removal 46
  • soybean by the bushel K removal 63
  • wheat by the bushel K removal 23

Suggested management practices for K vary with each crop.

  • Top dress applications are appropriate for perennial crops such as alfalfa and grasses.
  • For soybeans, broadcast applications incorporated before planting are most effective.
  • For corn and wheat either banded or broadcast applications can be used
    • Broadcast rates can be reduced by one half if banded applications are used for these crops.
    • This management practice does not reduce yields but results in a savings of fertilizer dollars.

For crops (alfalfa and corn silage examples) that use lots of potassium and for soils with low potassium amounts.

  • Soil test and monitor these soils often to ensure proper levels and availability.
  • Top dress potassium.

No till or reduced tillage crop systems - These crop systems can cause compaction and reduced soil temperature which leads to less K availability.

  • Soil test and monitor these soils often to ensure proper levels and availability.
  • Top dress potassium.

Too high Potassium

  • High potassium in forage crops can be problematic to farm animals.
    • Dairy cows can get milk fever for example.
  • Consider the potassium levels in the soils and how it relates to your plants and farm animal dietary needs.
  • Decrease in uptake of other nutrients can result with too high K in the soils.
  • Potential nutrient pollution of surface water through erosion of the nutrient-rich soil.
    • Potassium is not a problem pollutant, but when soil K levels are built up by applying manure, soil phosphorous levels are also likely to be high.
  • Reducing soil K in soils is to keep removing it, typically by utilizing crops with a high K requirement, without continued application.
  • Can cause a depression of magnesium (Mg) uptake by cool season grasses.
    • This can lead to grass tetany, a potentially fatal condition for ruminant animals.
    • Its effects are related to nitrogen fertilization, low soil temperatures, and animal physiology.
    • Grass, especially in fertilized pasture, accumulates K during the period of lush growth in May and early June, but Mg (magnesium) uptake is hindered by soil temperatures below 60 degrees F.
    • Grazing cattle get a high K diet that increases their need for Mg,
      • This results in a nutrient imbalance in the animals.
  • Guarding against grass tetany involves pasture and animal feed management.
    • The potential for this condition is greatest in pastures composed totally of cool season grasses.
      • Legumes accumulate Mg, even at soil temperatures below 60 degrees F.
    • High K forages can also result in increased incidence of milk fever if these forages are fed to dry cows.

 

Union Break!

photo.jpg Overheard - Flow

End of Union Break!

 

 

Potassium Deficiency

photo.jpg LDSPrepper - POTASSIUM DEFICIENCY IN PLANTS: Symptoms & Treatment

 

With a K deficiency the seasonal duration of leaf photosynthesis is shortened, transport of nutrients and sugars within the stem is hamstrung, plant integrity is compromised, starch formation is hindered, and use of nitrogen is limited. 

  • K is mobile and shows on older leaf growth.
    • At the bottom leafs of the plant.
    • The plant will take K from the lower leaves and transport them to the top leaf growth.
  • Classic signs are a yellowing or chloro-sis from the leaf tip then around the leaf edges 
    • Can be spots to streaks of yellow or white depending on plant type.
    • Research and understand the K deficiency for your crops and plants as various difference can be illustrated.

Leaves already showing deficiency symptoms cannot be restored by adding K.

  • Yield potential yield has already been reduced by the time the deficiency symptoms appear, and the plant has become more susceptible to the effects of other stresses.
    • Yield and quality of the crop is directly affected.

If insufficient K is available, characteristic symptoms of deficiency are likely to be evident during rapid crop growth.

 

Photo Examples

medium.leafyvegetables-def-potassium.png

Romaine Lettuce

 

medium.59c29d7948bc4_Kdefiencyinlettuce.

Lettuce

 

medium.59c29d6e17625_potassium1-1deficie

 

 

medium.59c29e632589a_Kdefiencyinrice.jpg

Rice

 

medium.59c29e63a6e71_Potassiumdeficiency

Corn on the Cob

 

medium.59c29d7145d11_potassiumcorndefici

Corn Leaf

 

 

Potassium Application

photo.jpg Gary Pilarchik (The Rusted Garden) - Understanding Garden Potassium: What it Does, Greensand, Banana Peels & Other Forms

 

Organic options for Potassium

  • Compost - Especially with adding banana peels. 
    • Usable to the plant immediately.
    • Easily leached. 
  • Wood Ash - Hard wood ash
    • 5 gallon bucket will treat about 1000 square feet.
    • Can be added to compost to boost potassium levels of the compost.
    • Caution - will raise PH levels.
  • Kelp Meal and seaweed - Dry or Liquid form
    • Easily available to the plants.
  • Greensand - Mined from ancient sea beds.
    • Can be used as a fertilizer or used in compost.
  • Muriate of Potash (potassium chloride)
    • Contains chlorine which is harmful to soil microbes.
  •  Sulfate of Potash
    • Similar to muriate of potash but generally more expensive
    • Does not contain chlorine and is safe to soil microbes.
    • Not all sources of sulfate of potash is truly organic.
  • Sul-Po-Mag - A variation of potash, sulfate of potash-magnesia
    • A natural version is langbeinite 
    • Is water soluble and immediately available to the plant
    • Can leach
    • Generally is not used unless you need sulfur and magnesium.
  • Granite Dust
    • Is very slow potassium and tract mineral release.
      • Not a sufficient source of potassium on its own.
    • Can be added to compost piles.

 

Manure Potassium

Manure is a K resource present on most farms.  However, K concentration varies by water and bedding content.

  • Manure nutrient analysis is the only sure way to manage amounts of applied manure nutrients.
  • Potassium in animal manure is almost totally dissolved in the liquid fraction, so it is important to conserve this portion of the manure. As long as liquid is not lost, handling and surface or incorporated application do not affect K content or availability.
  • If a soil sample is taken after manure application, then the available manure K will be reflected in the soil test level and recommendations.
  • If, however, manure is applied after soil sampling, then manure K should be subtracted from the recommendations on the soil test report.
  • Manure K is immediately available and may be considered a 1:1 substitute for K fertilizer.

 

Manure Moisture (%) K2O (lbs/ton) Variation (%)
Cattle 85 10 36
Pigs 91 11 53
Poultry 30 30 39

The average K content of various animal manures.

 

Fertilizer Potassium

Potassium chloride (KCl), called muriate of potash is the most common fertilizer form.

  • It is a highly water soluble salt with a K2O analysis of 60 to 62 percent.
  • Processing differences result in two common chemical qualities, identifiable as red and white muriate of potash.
  • Because the difference is of no consequence to the plant, deciding which to use should depend on the basis of cost per unit of K.
  • The K analysis of a fertilizer material is given as the percentage of K2O (potash) for the material.
  • There is no actual K2O in fertilizer, but this is the accepted and legal reporting form. Potassium recommendations are reported as lbs of K2O per acre on a soil test report.
  • The units of potash (K2O) can be converted to potassium (K) by multiplying lbs of K2O by 0.83. For the opposite conversion, multiply lbs of K by 1.2 to get lbs of K2O.
  • Is incompatible with tobacco.

 

Potassium sulfate, with a K2O analysis of 50 percent, also supplies sulfur, but this is generally inconsequential since sulfur is rarely limiting for agronomic crops.

  • Solution fertilizers may use KOH as the K source.
  • KOH has a high K2O analysis, 70 percent,
    • the K is no more available to the crop than if KCl were applied.
    • Fertilizer solutions made with KCl may not be clear, but that is not a disadvantage from the plant’s perspective.

 

As a salt, K has the potential to injure plant roots.

  • Whether this becomes a problem depends on the rate of fertilizer or manure, especially poultry manure applied and its placement relative to plant roots.
  • Rainfall dilutes and leaches the salts in soil, reducing the risk of injury.
  • Because starter fertilizer is placed, by design, near seedling roots, this practice has the greatest potential for root injury.
  • You can avoid injury by reducing the rate or by placing the fertilizer farther from the seed.
  • Recommendation by Penn State is that total nitrogen plus K2O should not exceed 70 lbs per acre when the fertilizer is placed 2 inches over and 2 inches down from the seed row, and less if placed closer.
    • Except in low K soils, there has been little consistent benefit from banding K as a part of the starter application and, therefore, it may be best not to include K in starter fertilizer.

 

Summary

In soil fertility we are concerned with crop response.  We want to apply nutrients, K in this case, where we are most likely to get a profitable return. We have seen that crop response to K may be more indirect than direct.  Effects will be an increased response to nitrogen and improved resistance to disease, drought, and cold temperatures, and may, therefore, depend on growing season conditions.

In soil testing, we have a good, though not perfect, indicator of probable response to K. Soil testing partnered by good crop records enables management to make it effective. Then, by knowing the yield per field, growing conditions, problems, soil K level, and other factors, you can make decisions, based on realistic information for your crops and fields that will project into the coming years.

This is important when you rotate crops in a field, especially when those crops, like corn and alfalfa, have very different K requirements.  Managing nutrients makes better use of limited finances.  Manure needs to become a primary concern in nutrient management, because it is a readily available nutrient carrier on most farms.  Potassium needs to be used wisely to ensure an adequate supply for your crops, but not oversupplied in “insurance applications.”

 

Recommendations:

  • Test soil regularly, at least every three years or when changing crop.
    • The soil test reports the amount of available K and the K2O required, if any, to bring soil level up to optimum and offset crop K removal.
  • Evaluate the fertility program for each field by looking at the trend, over time, of the soil test levels in relation to the optimum range.
  • Plan ahead within a rotation to supply K for the crop with the larger requirement.
  • Reduce soil erosion with soil and water conservation practices,
    • Do not stockpile nutrients in fields prone to erosion.
  • Conserve the liquid portion of the manure with bedding or leak proof storage to conserve the manure K.
  • Have farm manure analyzed for its nutrient content.
    • Apply manure uniformly and at a known rate as part of a planned nutrient management program.
    • Remember, quality in gets quality out.
  • Evaluate the need for K in a starter fertilizer relative to soil test levels.
    • At optimum or higher K levels, a response to starter K is unlikely.
    • Keep rate of K used in starter low, or keep K away from the seed to avoid salt injury to seedlings.
  • Keep good crop records and include input amounts, measured yields, and production costs.

 

:books:

Managing Potassium for Crop Production (PDF) - Penn State Extension

 

 

Credits:

 

:awesome-smiley-emoticon:

congratulations for learning about Potassium in soils and plants

 

Links

 

medium.roots.jpg.5509406fdf87b4693452d90029b8c1fa.jpg

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