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Contents
Cost saving pressures
Don't be fooled by appearances
Why potash is important
N:K partnership
Why maintain soil reserves
Soil analysis
Principles of potash use
Current economics of potash use
PK balance
Recommendations kg/ha
What value straw?
Conclusion
More information
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Watch your P's & K's for cereals

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Current economics of potash use

  A general guide to the economic return of potash use is as follows:-  
  K index 0 £10 return for every £1 spent on potash  
   
  K index 1 Up to £5 return for every £1 spent on potash  
   
  K index 2- Replace potash removed or index will fall to 1  
   
  K index 2+ Cost saving opportunities for reducing potash  
       

PK balance

Fertiliser use should be related to P and K removal and this is substantially altered if straw is removed. Phosphate is considerably more expensive per kg than potash and if P and K use is not properly matched to requirements, expenditure can be higher than necessary.

Typical phosphate & potash removal in cereals
      Phosphate Potash Ratio  
      kg/t of grain kg/t of grain P2O5 : K2O  
  Grain only - All cereals 7.8 5.6 1.4 : 1  
  Grain + Straw            
  Winter wheat/barley 8.6 11.8 1 : 1.4  
    Spring wheat/barley 8.8 13.7 1 : 1.6  
    Oats/rye/triticale 8.8 17.3 1 : 2.0  

Recommendations kg/ha

P2O5 & K2O
  Low fertility soils  
  P or K index 0 Add 50 kg/ha to the replacement quantity  
  P or K index 1 Add 25 kg/ha to the replacement quantity  
  Target fertility soils  
  P index 2 K index 2- Use replacement quantities  
    Multiply yield (t/ha) x removal figures (see above) = replacement  
  Above target fertility soils  
  K index 2+ Deduct 15-25kg/ha from the replacement quantity
  
  K index 3 Nil K where straw incorporated. Deduct 60-70 kg/ha from the replacement quantity where straw removed  
  P index 3 Deduct 40-50 kg/ha from the replacement quantity  
  Over high fertility soils  
  P or K index 4 No P or K fertiliser application required  

 
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