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Potash for Organic Growers

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Certification of sources of potash

Council Regulation (EC) No 834/2007 of 28 June 2007 on organic production and labelling of organic products and repealing Regulation (EEC) No 2092/91 sets out the rules for organic production for all countries in the EU. Growers must register with an individual certification body and comply with the requirements of that body (which may be stricter than the EU legislation). The certification bodies operating in the UK and Ireland are:

UK:

Ascisco Ltd
Bio-Dynamic Agricultural Association
Organic Farmers and Growers Ltd
Organic Food Federation
Quality Welsh Food Certification Ltd
Scottish Organic Producers Association
Soil Association Certification Ltd

Ireland:

Irish Organic Farmers and Growers Association
Organic Trust Limited

The regulations require as a first choice the use of organic material from organic holdings to maintain, or improve where appropriate, (potassium) fertility of the soil. However the Regulations restrict applications of animal manures to a farm limit of 170 kg N/ha and UK certification bodies also apply a 250 kg N/ha field rate. Other permitted sources of potash are classified as follows:

      Permitted materials
   

Manures from non-organic but extensively run holdings.
Variable potash content.
Around 90% of total K2O immediately available.
Sustainable, natural, not manufactured materials.
Also provides organic matter and other nutrients.
   

 

Wood products not chemically treated after felling (ash, sawdust, bark).
Variable, low potash content 1-7% K2O.
60-90% of total K2O immediately available.
Natural materials.
Also contain some other nutrients.
  Products and by-products of plant origin
   

 

Straw (Own or imported from any other farm only for bedding purposes).
Variable, low potash content 1-2% K2O.
60% of total K2O immediately available.
Sustainable, natural.
Also provides some organic matter and limited other nutrients.
   

Kali vinasse (Imported by-product from sugar beet molasses industry).
Up to 40% K2O as K2SO4. Also contains SO3 and traces of other nutrients.
Totally soluble. Nil chloride. Fine powder.
Marketed as Law's High K by Law Fertilisers Ltd, as a granular product
containing 30% K2O with other nutrients.
   

Composts free from prohibited materials.
   

Seaweed and seaweed products; low K2O content.
  Stone meal (rock potash)
   

Highland potash marketed by Glenside Organics.
Adularian shale feldspar mined in Scotland.
Total K content 9-11% K2O.
Very limited plant-availability by conventional measurement.
  Crude potassium salts
   

Sylvinite produced by Cleveland Potash Ltd.
16% K2O soluble salt.
Natural, mined, crushed and screened UK product.
Contains NaCl + KCl and some trace elements.
   

Magnesia-kainit marketed by Potash Ltd.
11% K2O soluble salt, also known as magnesia-kainit.
Natural, mined, crushed and screened imported product.
Also contains 27% Na2O, 10% SO3 and 5% MgO.
   

Sulphate of potash (SOP), K2SO4
50% K2O soluble salt. Also contains 45% SO3
Imported processed or manufactured product.
Easily spread 1.6-4 mm high quality granulated imported product.
Nil chloride.
   

Permitted where need is recognised by the inspection body.
   

Permitted by Soil Association on soils with less than 20% clay and where
K index is less than 2. Permitted by other inspection bodies, on soils with
less than 20% clay at K index 1 and on all soils at K index 0.

 

    Prohibited materials
   

Manures from intensive non-organic units.

Muriate of potash (MOP), potassium chloride, KCl.
60% K2O soluble salt.
Natural mined, crushed, separated, compacted and screened product.
Easily spread 2.6 - 4 mm high quality compacted granular product.
  Ashed poultry litter.
   

e.g. 'Fibrophos' marketed by John Hatcher & Co Ltd.
14-24% K2O, 70-100% available.
Powdered slag-like by-product of poultry litter power stations
Also contains useful levels of phosphate and a range of other nutrients.
This material is allowable where it is derived from litter from organic production units.

Compounds, blends, solution and suspension fertilisers.
Prohibited where they contain other prohibited materials.

Practical approach

The correct approach for both organic and non-organic systems is to monitor soil fertility every 4-5 years by soil analysis and by drawing up a nutrient balance calculation- this will not only demonstrate good practice, but will provide evidence to justify the use of restricted materials, if necessary. Allocation of manures and use of fertiliser materials should be undertaken to maintain available soil potassium (and similarly phosphate) appropriate for the crops being grown (see PDA Leaflet 8: 'Principles of Potash Use'). Where soil potassium (and phosphate) status is satisfactory, nutrient policy should simply be to replace nutrients removed, using estimates based on the standard offtake data (see PDA Leaflet: 'Phosphate and Potash Removal by Crops'). It should be noted that even the most efficient storage and recycling of organic manures may not provide adequate replacement because of the export of nutrients in products sold off the farm and retention of some of the applied nutrient in non-available reserves.

 

 
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