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Sulphur the forgotten nutrient

Sector News Sector News16-3-2018

Sulphur is often overlooked when it comes to grassland and especially silage, the focus so often being on Nitrogen, Phosphorus and Potassium. However Sulphur is present in all crops and plays an essential role in plant metabolism and the formation of plant protein amino acids and and enzymes. 

Until relatively recently, Sulphur deficiency wasn't seen as an issue. Depositions of atmospheric sulphur as sulphur dioxide from the burning of fossil fuels guaranteed a plentiful and free supply for UK farmers. But tightening legislation saw deposition greatly reduce, so much so that deposits have declined by 94% since 1970. Government figures suggest that 6.8kg/ha of sulphur are now deposited annually on UK grassland and bearing in mind that an average silage crop requires 40kgSOᶟ/ha/cut, sulphur deficiency in grassland is a very real but not always apparent issue. 

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Sulphur Deficiency

Sulphur deficiency will typically occur under the following conditions:

  • High winter rainfall (leaching of residual S)
  • Light or sandy soils
  • Low organic matter soils
  • Little or no organic material (FYM or slurry) applied
  • Insufficient or no inorganic (bagged) sulphur applied

Where silage crops receive sufficient sulphur they will:

  • Be of better quality
  • Proteins will be higher
  • Sugars will be higher
  • Conserved silage will be more digestible
  • Have a higher total N content but lower free nitrate content having used the available nitrogen more efficiently
  • Achieve expected or improved dry matter yields due to efficient utilisation of nitrgoen. Up to 30% average response across all soil types and all cuts is not uncommon
  • Be more drought tolerant, displaying improved water retention qualities

All cuts respond favourable to sulphur but especially 2nd and 3rd cuts

Top Tips for...

Soil Chemistry

  • Analyse your soils regularly. Of 500 soils recently analysed by ForFarmers advisors, 94% were below target index for Sulphur. Additionally soils not at target pH 6.2 will have reduced availability of P, K and S, so correcting soil pH is key to efficiency

Plan Ahead

  • Analyse slurries, test soils and make a nutrient management plan, based on your class of stock, silage quality and yield expectation
  • Purchase the correct fertilisers for your needs taking into account manures and the sulphur needs of your silage crops
  • Apply in a timely fashion and allow 40kg/ha SOᶟ/cut especially for 2nd and 3rd cut

Measure

  • Use fresh grass analysis to monitor N : S levels indicating deficiency or sufficiency
  • Plan to correct deficiencies both short and long term

When yield, quality and nutrient efficiencies are considered investment in sulphur for grassand and in particular silage crops will generate a significant return on investment. Recent studies suggest a typical response of up to 30% and as much as £20 return for every £1 spent on sulphur.