Biological Binge, Understanding Potassium's Role  01/09/19 9:57:27 AM

 

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Soil Element of the Week--Potassium
 
We have all been told for many years Potassium (K) effects standability in crops. As it turns out Potassium plays a major role in many additional physiological functions within the plant. Potassium is a mobile nutrient in plants, actually, all three primary nutrients: nitrogen, phosphorus, and potassium are mobile in plants.
 
Potassium is absorbed by plants in larger amounts than any other nutrient except nitrogen.  In our neck of the woods, it rarely leaches in the soil, and it is released as the K+ ion.  High clay content and high organic soils are also often potassium deficient because they contain few of the minerals that weather and release K+.
 
Potassium plays an essential role in photosynthesis, carbohydrate synthesis and transport, and plant metabolism.  It encourages cell wall thickness and stalk strength and plays a role in reducing overwintering injury in perennial crops.  It also regulates stomatal opening and thus transpiration and water loss in plants.
 
Many potassium level recommendations can be based on the Cation Exchange Capacity (CEC) of the soil being tested—as your CEC increases, your levels on K would also increase.  Generally, the amount of K2O needed to raise a soil test level by 1 ppm can range from 4-10 lbs. of K2O/acre—soil dependent…..Shooting from the hip, not knowing the soil type, etc.—the use of 7 lbs of K2O/acre would be a good stable amount to use.
 

CEC Target K in ppm
0-5 150
6-10 175
11-15 190
16-20 200
21-25 210
25+ 225
 
Optimum levels of Potassium are dependent on soil type, crop, yield goal, etc.  Light-colored and course textured soils may have an optimum range of 150-175 ppm in the soil while dark-colored and heavier textured soil types would have an optimum range of 175-200 ppm.
 
Deficiency symptoms appear in older leaves.  Symptoms on alfalfa are a series of white dots near leaf margins which later turns the entire leaf margin white.  Similar symptoms appear on soybeans where the leaves turn yellow and later brown on the tips and edges.  The base of the leaf usually remains green.  On corn, the lower leaf tips and margins turn yellow then brown.  The leaf midrib stays green as opposed to N deficiency symptoms.
 
 
With little to no field work conducted this past fall due to the wet soil conditions and pro-longed harvest, we now look to suitable conditions to apply fertilizer/lime/anhydrous and or conduct some seedbed preparation via tillage—if needed.  You may be considering tillage to dry out a few wet acres, maybe combat the ill effects of soil compaction, our “throw in” some of the rutted areas as a result of wet harvest conditions.   AS ALWAYS-- Plan to conserve as much soil moisture.  This may seem a little ridiculous at the time of the year and given our current soil moisture status, it might be also be considered counterproductive as wet as it has been in places.  But, we always need soil water and the more we can conserve pre-planting, the better.  Soil water capacity and availability depends on the soil type you have within the field. (See Table 1) as well as the tillage practices used on them.  I realize that certain soil types need to have some amount of tillage in order for active crop growth to occur. Most everyone agrees that the more you till a soil, the more moisture you lose at tillage depth—not to mention the damage to soil structure, water holding ability etc. that also occurs. 

 

Table 1--Available Water Capacities by Soil Classes

Textural Classes   Plant Available Water Capacity
in Inches/Foot of Depth
Coarse Sands   0.25 - 0.75
Fine Sands   0.75 - 1.00
Loamy Sands   1.10 - 1.20
Sandy Loams   1.25 - 1.40
Fine Sandy Loam   1.50 - 2.00
Silt Loams   2.00 - 2.50
Silty Clay Loams   1.80 - 2.00
Silty Clay   1.50 - 1.70
Clay   1.20 - 1.50
 
Most often, soils dry to the depth of tillage. It is bound to happen.  As seen in the above table, an average silt loam soil holds about 2 inches of plant available soil moisture per foot of soil. Tilling the soil can result in a loss of 1/2 to 3/4 inch of soil moisture with each trip dependent on the type of tillage and soil type involved. With multiple tillage trips, there may not be adequate soil moisture in the seed zone for uniform germination and emergence even though there may be sufficient moisture the rest of the year and below seeding depth.  Needless to stay, try to conserve your soil moisture.
 
The biological binge—For the last few years, there has been an increased presence of biological seed treatments in the market that promise a whole host of crop benefits.  Many can be used for both corn and soybean production., Many are hormone based combined with marginal amounts of micronutrients.  Many do not have much local data in our area to document the promises that are made.  So, in 2018 we conducted what we coin as a corn biological study, where we planted the same hybrid (DeKalb DKC66-75) at 8 separate locations.   Here is some back-ground on the 2 that we selected as treatments for our study

Treatment 1--Tripidity ST is a unique blend combining essential macro and micro nutrients and a proprietary blend of plant extracts to stimulate seed germination and to maximize early seedling growth and vigor. Tripidity ST also includes a balanced ratio of three hormones designed to work together to enhance seed germination and seedling establishment, provide stress reduction in cold soils, enhance cell elongation, and increase nutrient uptake for higher yield potentials

Treatment 2-- QuickRoots® technology helps maximize corn yields – especially in fields with limitations in moisture or nutrient availability. The microbes Bacillus amyloliquefaciens and Trichoderma virens help increase the availability and uptake of nitrogen, phosphate and potassium. The availability of additional N, P and K supports development of bigger roots, which helps increase uptake of moisture and nutrients to enable better plant growth and increased yield potential.


These locations were planted at multiple populations, different planting dates, soil types, etc.  Here is what we found in 2018
2018 Corn Biological Study--(8 Reps/locations) DeKalb DKC66-75 base genetics
      Ave. Yield    
Trt     Bu./Acre      
Untreated   245.5      
Tripidity     238.5      
Quickroots   233.8      

 
Now, this is again 1 year’s data and has no statistical worth, however, it is about as real-world as we can make it. 

 

 

 
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