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Blue Bags Grow Better Crops

Grassland R&D- Blends vs Compounds

Are you suffering yield reductions from using blended fertilisers on grass?


Blended compound fertilisers are cheaper than True Granular Compounds, but an uneven spread of nutrients from a blend can lead to yield penalties.


Spread test data on blends in 2015 shows the problem:
For a blended 25.0.13 (7.5 SO3) fertiliser, the actual analysis of the fertiliser landing at each point of the bout revealed a variation in N content ranging from 25% to 21%, so that at the outer halves of the spread pattern, the N content of the fertiliser was much reduced.

 Variation in a Blend vs a True Granular Compounds FertiliserVariations in spread width of a blend vs compound fertiliser

 

Variation in N Application of a blend vs compound fertiliser

This means that 14% less Nitrogen than planned was being spread over half the bout width.

 

It costs more than you save…

  • On a grassland system applying 250kg N/ha (200 units/acre), a 14% reduction in N application on half the area can result in a loss of 450kg grass DM/ha (360kg grass DM/acre). 
  • With a blend at £240/t and a True Granular Compound at £255/t, the cost saving in fertiliser is £15/ha(£6/acre). These figures are comparing a blended fertiliser with 25% N content. 
  • But at an average of 11.0 ME, the lost grass from reduced yield has enough energy for 670 litres of milk production per ha, or 77kg of liveweight gain.
  • And to replace that energy in concentrate feed would cost £77/ha (£31/acre), or to buy-in silage to replace the loss would cost £35/ha (£14 /acre). 

So, in this example, for every pound you save in using a blended fertiliser, you lose between £2.40 and £5.30, depending on how you handle the grass yield loss. At £2.40 a blend would need to be £35.00/t less.

 

Why do True Granular Compounds (N,P,K,S) and blends differ in spread pattern?


Blends and True Granular Compounds differ in two ways:


1. The particles in blends are more varied in size, shape and weight, so they fly off the spreader with more variation than the particles in a True Granular Compound, leading to wide variations in nutrient spread pattern.
2. True Granular Compounds have the same chemical nutrient analysis in each granule, whilst the particles in blends have very different nutrient analyses. This means that the nutrient spread from a True Granular Compound is more even and every piece of the field gets the same nutrients.

 

Blending K (potash chips and S (ammonium sulphate crystals) can be a particular problem, but not for a CF Fertilisers True Granular Compound Fertiliser.

 

 

Inaccurate spreading with blends reduces grass quality as well as yield.

Grass Quality Striped Area Non-striped Area
Dry Matter (%) 17.6 17.0
Crude Protein (%) 15.7 24.2
D Value 73 80
ME (MJ/kg DM) 11.5 13.6
  • 2015 example from dairy farm
  • NK blended fertiliser
  • Applied after 1st cut silage for 2nd cut growth
  • Nitrogen in the blend did not spread evenly over the 24m bout

 

 

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