Fertility Building Christine Watson

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Fertility BuildingChristine Watson
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Talk structure

• Fertility building crops
• Nutrient budgets
• Soil analysis

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N fixed and remaining after harvest
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Effect of period of crop growth on N return from
fertility building crops (Rayns et al. 2002)
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Effect of rotational position on spring barley
yield (Rayns et al. 2002)
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Using legumes
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Managing legumes
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Nutrient budgets
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Getting the balance right
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What is a nutrient budget?

• Nutrient budgets summarise the inputs and outputs
  of nutrients to a farming system.
• They are simple calculations based on the idea of
  mass balance
• Inputs - Outputs Change in reserves

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Nitrogen budget
Average 98kg/ha
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Phosphorus budget
Average 5 kg/ha
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Potash budget
Average 1 kg/ha
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Average nutrient budget kg/ha
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Without manure, what are the options?

• Green waste compost
• Sewage sludge
• Supplementary nutrients- Rock P and K are very
  long-term solutions, are they sustainable?-
  Potassium sulphate may be allowed but is it
  desirable?

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N, P and K contents of organic materials
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Nutrient budgets

• Nutrient budgets are useful indicators of how
  efficiently nutrients are being used in the
  system
• Nutrient budgets are best used with soil analysis
• Building soil organic matter is always a priority!

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Routine soil analysis

• Only as good as your samplingwhere, when,
  depth.
• pH,
• Available K, available Mg, available P(Often
  given as an Index value)

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pH

• pH, log of inverse H concentration soil
  acidity
• Soil pH has no precise value or unambiguous
  interpretation
• Must be measured using standard procedures
• Mostly affects plant growth indirectly through
  influence on nutrient availability and presence
  of toxic ions

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Optimum pH?

• Microbial populations adjust to pH, but prefer
  moderate conditions
• Phosphorus never readily soluble, but held with
  least tenacity around pH 6.5 rock phosphate more
  soluble at lower pH
• at pH less than 5, available aluminium and iron
  may reach toxic levels

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Soil nutrient pools
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K and Mg
K
Mg2
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P is more complicated.

• Why? Because it is not just about chemical
  availability!
• Soil micro-organisms play a key role - bacteria
  and fungi both very important
• Plants are competing with the soil biology for
  available P
• Good soil structure very important

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Stockless arable/horticultural rotation
Compost
Grass/clover ley
Grass/clover ley
Spring barley
N, P, K
Potatoes
Vetch - cover
Onions
Rye - cover
N, P, K
N, P, K
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The End! Thank-you for listening!
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N fixation