Blueberry Council of Missouri

 

Blueberry Council of Missouri Newsletter

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KP and that’s not Kitchen Patrol

Editor: Howard Thompson
September 2009

Last month we talked about nitrogen’s effect on blueberry growth and health. It was noted that for blueberries, nitrogen is more likely to be deficient in Missouri than either K or P. It was also noted that all forms of nitrogen fertilizer are not created equal for blueberries. This month I would like to finish off the discussion of the tow remaining major plant nutrients, P (phosphorus) and K (potassium) which are usually not deficent in Missouri soils.

Phosphorous

In photosynthesis, phosphorus in the form of phosphate (PO4-) is added to adenosine diphosphate(ADP) to make adenosine triphosphate(ATP). Phosphorous (PO4) is an integral part of Nicotineamide Adenine Dinuclotide(NADPH) which is envolved in the oxidation and reduction reactions in the cells with NAD+ being the precursor molecule. These chemicals ATP and NADPH becomes the energy source that runs the cells. With the addition of carbon dioxide (CO2), the extra energy is stored in the form of glucose and other carbohydrates while the ATP and NADPH return to their precursor chemicals. In otherwords, the cells are continually recycling ATP/ADP and NADPH/NAD+ to drive the metabolism of each cell. Without the transfer of phosphates between molecules and its associated energy, the cell would not be able to make; proteins, nucleic acids (RNA and DNA), and sugars which is store as starch and cellulose(part of the cell wall). The cell can not even make a cell membrane since it is made of a double layer of phospholipids. Beside the fact that photosynthesis does not work well when there is a deficiency of P, without these basic building blocks that contain P the plant to have major problems that is exhibited in stunted growth, poor root growth, poor flower production which results in poor yields and small fruit since this is a plant function that requires high amounts of energy and new genetic material.

Beside poor growth, the leaves of the plant turn a shade of purple that looks more like maroon. This is more noticeable in the early spring and corrects as the temperature warms up and the plant is better able to absorb the phosphorus from the soil. If you have been overzealous with adjusting you pH, a highly acidity soil will bind the phosphate to iron and aluminum. This may require P2O5 fertilization even though the soil sample indicates that there is adequate phosphorus to overcome the natural P fixation. Below are two tables from Spectrum Analytic (Table 1 and 2) that presents what is a “good P” in soil for blueberries. Unfortunately, excessive P can interfere with micronuritients absorption (Fe, Zn, Cu and Mn). The best way to determine if the plant has sufficient P is a tissue sample. Unfortunately according to Oregon State, there in no accepted optimal tissues range for P but at the same time they are will to present their standard (table3)

Soil P Status
CEC 0.1 5 10 15 20 25 30 35+
PHOSPHORUS (lb./acre): soil target pH <6.0
Low 70 60 54 50 47 44 43 40
Medium 140 120 109 102 95 89 83 80
Good 210 180 169 159 153 148 144 140
High 280 240 229 216 211 207 205 200
V High 400 340 316 293 281 274 270 26

Soil P2O5 Recommendations
Soil P Status Yield Goal (cwt/a)
  20 40 60 80+
  lb P2O5/acre
Low 150 162 166 171
Med 75 89 93 98
Good 5 10 15 20
High 0 0 0 0
V High 0 0 0 0
Soil P Status
Spectrum Analytical

Table 3.- P fertilization rates based on soil and late July to
Mid-August tissue sampling.
Apply this amount
Soil test P (Bray) (PPM) Leaf P of (%) P2O5 (lb/a)
0–25 below 0.07 40–60
26–50 0.08–0.10 0–40
above 50 above 0.10 0

Unlike the rapid plant response one can see by applying nitrogen, the same can not be seen with phosphorus since the movement in the soil is very slow. This means, do not expect a change in the tissue level for at least one year or more after application.

Potassium

Potassium is a positively charged electrolyte than is a kissing cousin to sodium that moves relatively freely across cell membranes. It does not actually become part of the structural part of the plant. It is a cation in the cytoplasm, nucleoplasm and sap. Its primary movement is driven by concentration gradient across the membrane. It also moves by active and facilitated transport. The later two forms of transport move against the concentration gradient which is analogous of pushing a bolder up a hill. This requires energy in the form of adenosine triphosphate(ATP) and glucose to move it against the concentration gradient and a “protein pump”. Water follows the concentration gradient of the electrolyte which analogous to one eating well salted chips and then requiring larges glasses of water. Along the same lines, on the underside of the leaves that are small pore structures called stomata that open and close based on how much water is in the leaf. These pores are affected by the potassium concentration. When the cellular concentration is “high”, the stomata close cutting water loss and opens when the concentration is “low”. Besides controlling the turgidity of the plant, the outflux of water though the stomata help pull nutrients up from the roots. As the fruit matures, the levels of potassium in the plant increase. This means, if there is a particular heavy yield, the plant may see a deficiency. Also, potassium in the fruit is important for the quality of taste of the fruit much analogous to some people putting salt on watermelon. Finally, it has been shown the potassium help fend off disease.

There are several factor that affect the potassium level in the plant and it all starts and end in the soil. Soil high in organic matter and/or clay content will hang onto more cation (positively charged ions like K+, Ca+2, Mg+2). Since we strive for a soil pH around 4.5 this means there is high soil concentration of H+ which makes K+ less available to the plant. Anything that makes the K+ less available to the plant would require a high amount of K+ to be fed to the plant for the desired effect. Finally the weather affects potassium availability. In early spring when the temperature is cool, the less the plant can use what is there. Since K is water soluble, without adequate soil moisture, it cannot get to the plant.

Fortunately K+ deficiency in Missouri is very uncommon. It symptoms may be just scorching of the leaves and die back of the tips. But since it is involved with internal water balance and disease resistance, these symptoms may not be obvious until late July to September, when parts of Missouri get very little rain and we are relying on irrigation. The best method to asses the tissue potassium level is a leaf sample which should be done (any time now). If the tissue level suggest a lower than optimal K+ (Table 5 from Oregon State), this suggest a increase in the application of potassium in the spring. Just like with nitrogen all forms of potassium are not equal for the blueberries. Table 5 show the forms of potassium that is available. There is Potassium Nitrate (KNO3) and Potassium chloride (KCl) also called potassium muriate available, but both are toxic to blueberries. Since there are many anions in the soils that hold the potassium in the soil, it does not move freely, so just like phosphorus, it may take 1-2 years to see a change in the tissue levels.

Table 6.—K fertilization rates based on soil and late July to
mid-August tissue sampling.
Apply this amount
Soil test K (PPM) Tissue K of (%) K2O (lb/a)
0–100 below 0.20 75–100
101–150 0.21–0.40 0–75
above 150 above 0.40 0

Typical Chemical (Table 5)
Product K2O Analysis Formula
Potassium Sulfate 50-54% K2SO4
Sulfate of Potash Magnesia
(K-mag/Sul-Po-Mag)
11% K2SO4•2MgSO4
Potassium Carbonate 34-48 K2CO3
Potassium Metaphosphate 39 KPO3

Soil K Status Tables
CEC 0.1 5 10 15 20 25 30 35+
POTASSIUM (lb./acre)
Low 90 90 120 150 165 180 200 225
Medium 180 180 240 300 340 380 400 452
Good 270 270 380 460 530 570 615 660
High 400 400 545 690 777 864 930 978
V High 401+ 401+ 546+ 691+ 778+ 865+ 961+ 979+

Spectrum Analytic

The bottom line for the major nutrients (N, K and P) for blueberries is a follows: all forms of fertilizer are NOT created equal which mean reading the labels before purchases. Also regular program soil testing and leaf evaluation will help control your cost and protect your plants. Finally, NOW is time for a leaf analysis (review the July issue for the proper collection procedure).

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