Potato Review Group

Contents

Background:

Physiology

Deficiency symptoms and effects

Sulphur requirements

Application of sulphur to soil:

Form of sulphur to apply

Sulphur containing fertilisers

Rate of sulphur application

Measurement of sulphur concentration in soil

Measurement of sulphur concentration in foliage

Further information:

Sulphur notes

 

Background

Physiology

  1. Sulphur is a constituent of protein and deficiency therefore results in reduced protein synthesis.
  2. Reduced synthesis of chloroplast proteins can result in chlorosis and reduced carbohydrate production.
  3. Sulphur deficiency can increase susceptibility to diseases. More …
  4. Application of sulphur is not an efficient means of reducing the risk of common scab.

Deficiency symptoms and effect

  1. Chlorosis occurs first in the youngest leaves, in contrast to N deficiency.
  2. There may be an overall reduction in growth: plants may be rigid, brittle and with thin stems, leaves may be narrow.
  3. Sulphur deficiency has been shown to reduce the concentrations of cysteine and leucine but increase the concentrations of glutamic acid and argenine. More … 
  4. Glutamine and argenine may be particularly important in the Maillard reaction between sugars and amino acids, resulting in a dark colour when potatoes are fried. See also Tuber processing quality.

Sulphur requirements

  1. Sulphur deposition from the atmosphere has declined so application may be required.
  2. Sulphur requirements should be calculated in relation to nitrogen requirements.
  3. This can be measured as N : S ratio in foliage or in soil.
  4. The minimum requirement is an N : S ratio of 14 : 1.
  5. An average requirement is an N : S ratio of 11.5 : 1.
  6. The maximum requirement is an N : S ratio of 10 : 1, which may reduce susceptibility to diseases in addition to providing sufficient for crop growth.

Use this link for more information on the background to sulphur requirement.

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Application of sulphur to soil

Form of sulphur to apply

  1. Sulphur should be applied in the form of sulphate fertilisers, as elemental sulphur requires oxidation to sulphate and its use is therefore inefficient.
  2. Sulphate fertilisers may help to slightly acidify the ridge and help to provide some suppression of common scab infection but this is not a reliable means of control.
  3. Oxidation of elemental sulphur applied to soil is influenced by:
    • temperature (rate increases at higher temperatures)
    • particle size (greater availability the smaller the particle size)

but not by:

    • pH
    • organic matter soil
    • calcium

the rate of oxidation is generally too slow for availability within the season of application.

Sulphur containing fertilisers

S fertilisers

Rate of sulphur application

  1. The rate of sulphur application should be calculated to provide the required  N : S ratio in soil, e.g. of 10 : 1.
  2. For example 320 kg N ha-1 = 32 kg S ha-1
  3. Sulphur nutrition of a crop may be checked as the N : S ratio (10 : 1) in foliage or as a concentration in leaves of > 0.28 %.

Measurement of sulphur concentration in soil

  • The amount of sulphur in soil (kg S ha-1) is calculated as follows:

Ssoil = [S ppm (0-30 cm) * 3.6] * Fsoil + [S ppm (30-60 cm) * 4.2] * Fsoil

where Ssoil (kg S ha-1) is measured as ppm S in samples taken from 0-30 and 30-60 cm depths and Fsoil is the fraction of the sample which comprises soil, e.g. if stone content = 10 % Fsoil = 0.9

  • To achieve an 10 : 1 ratio of N to S, the amount of sulphur fertiliser required, Sfertiliser (kg S ha-1), is calculated as follows:

Sfertiliser = [(Nsoil + Nfertiliser) / 10] – Ssoil

where Nsoil is the amount of soil residual nitrogen (kg N ha-1 ) and Nfertiliser is the amount of fertiliser nitrogen applied (kg N ha-1 ).

Use this link for more information on the sulphur application.

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Measurement of sulphur concentration in foliage

  1. Measure concentrations of sulphur and nitrogen in the youngest fully expanded leaf.
  2. If the ratio of N : S is higher than the target (e.g. N : S > 10 : 1), sulphur is deficient.

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Further information

Sulphur notes

Sulphur for potatoes 2013 (Includes sulphur physiology and use of N : S ratios)

Nutrient interactions 2010 (Includes role of sulphur in plant defence mechanisms)

Sulphur nutrition 2001 (Sulphur for yield and tuber internal quality)

 

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