Saturday, November 10, 2012

What Potash Source Should I Use?

 Soils in the western U.S. are becoming depleted of potash.  Soils in this part of the country were commonly high in potassium when they were first cultivated long ago.  However, after many years of intensive cropping and repeated nutrient removal, many fields now require regular inputs of potash to maintain high levels of production.  High yielding crops remove large amounts of potassium in the harvested portion of the crop.

It’s little wonder that K deficiencies are becoming a common occurrence in so many fields.   For example, harvesting 9 ton alfalfa/A will remove over 450 lb K2O.  Similarly, a potato yield of 450 cwt/A removes 500 lb K2O and harvesting 40 ton/A of tomatoes will take off over 450 lb K2O/A.  But this high rates of nutrient removal is not being matched with fertilization.  In Idaho, for example, an average of four pounds of potash are removed in crops for every pound that is added back.  In the Pacific coast states, over two pounds of potash are removed on average for every pound returned to the field as fertilizer.

There are many excellent sources of potash to replenish the soil’s nutrient reserve.  Some of the most popular include:

  • Potassium chloride (Muriate of potash)     (KCl; 0-0-60)
  • Potassium sulfate (Sulfate of potash)         (K2SO4; 0-0-50- 18S)
  • Potassium-magnesium sulfate                    (K2SO4-2MgSO4; 0-0-22-22S-11Mg)
  • Potassium thiosulfate                                  (K2S2O3; 0-0-25-17S)
  • Potassium nitrate                                         (KNO3; 13-0-44)

How are these sources different?
The potassium in all these fertilizers is identical and this nutrient will be rapidly available to the plant regardless of the source.  The primary difference is in the companion nutrients that come along with the potassium.

Potassium chloride can be red from traces of iron
Chloride  The importance of this essential nutrient is frequently overlooked.  Recent research has demonstrated that many crops respond favorably to chloride applications with greater yield and quality.  Like any soluble fertilizer, salt-induced damage can result if large amounts are placed in close proximity to seeds or seedlings.
White potassium chloride (MOP)


Potassium sulfate (SOP)
Sulfate All crops require an adequate supply of sulfur to develop proteins and enzymes.  Sulfur-deficient plants appear light green and have reduced yields. Sulfate that is present in potash fertilizers is immediately available for plant uptake, while thiosulfate rapidly converts to the sulfate form in the soil.

Langbeinite (K+Mg+SO4)

        Magnesium Because its vital role in chlorophyll, magnesium is first exhibited by yellow leaves in the lower part of the plant.  Magnesium requirements vary considerably, with legumes generally containing more of this element than grasses.

Potassium nitrate (NOP)

Nitrate An abundant supply of nitrogen is essential for all high-yielding crops.  For crops that prefer a nitrate source to an ammonium source of nitrogen, this potash source can be a good option.

There are many excellent potash sources available for meeting the nutrient requirements of crops.  When making a decision on which source to use, choose the one that meets your needs and provides the accompanying anion that will help keep your high-yielding crops in top shape.

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