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Sulphur Nutrition

Publication Date: 
4 August 2016

Sulphur is an important component of a complete and balanced crop nutrition plan. 

Previously, the supply of natural sources of Sulphur from the soil was regarded as sufficient for the potato crop. However, with significantly reduced sulphur deposits from the atmosphere (due to a marked decline in industrial pollution), and continued use of fertiliser with low sulphur content, sulphur deficiency has gained increasing attention in many regions causing crops to become vulnerable to yield reductions. 

Where deficiency does occur, it is most likely to show first in crops grown on deep sand soils with low organic matter and in areas that are well away from industrial pollution, however there are several factors to be considered in order to make an informed decision regarding a crop’s sulphur requirements. 

Sulphur, although classified as a secondary element is sometimes called “the 4th major nutrient” and is an essential nutrient in crop production. 

Crops with a high Nitrogen requirement will usually also have a high Sulphur need.  This is because both elements are involved in protein and chlorophyll formation and are linked in the conversion of nitrate to amino acids. 

Sulphur is necessary for protein and amino acid synthesis which aids effective utilisation of applied nutrients such as nitrogen. It also supports the production of chlorophyll and a plants resilience to disease. So with Sulphur such an important element in plant growth we need to be sure it isn’t a limiting factor reducing yield and quality.

The majority of Sulphur in most soils is contained in organic matter. This organic form of Sulphur must be converted (mineralized) to an inorganic form (sulphate anion) before it can be released and made available to the plant.  Sulphur release is affected by temperature and moisture.  Generally speaking conditions that favour crop growth will also favour the mineralization and release of Sulphur from the substrate. 

Effective nutrient management systems should seek to achieve an adequate but not excessive amount of nutrients available to the growing crop. 

Excessive application of any nutrient is inefficient and can have a negative environmental impact. Sulphate, like most anions, is somewhat mobile in soils and therefore subject to leaching.

With the increased attention on sulphur comes the need for a greater understanding of optimum sulphur requirements, soil-sulphur availability and the responses of potato crops to sulphur containing fertilisers.  

There have been very few replicated trials on sulphur nutrition for potatoes and there is a concern that the current advice might be outdated. Cambridge University Potato Growers Research Association (CUPGRA) has scheduled a series of three trials in 2016 to gather data for the AHDB’s review and update of the RB209 Fertilizer manual.  

The Strategic Potato (SPot) Farm at the Elveden Estate (SPot Farm East) has been selected as one of CUPGRA’s three trial sites and uses the variety ‘Russet Burbank’ grown on a site where sulphur availability might be expected to be low – a shallow sandy soil with low organic matter.

The Trial at SPot Farm East is a fully replicated and yielded to better understand the importance of sulphur nutrition in potatoes and has three treatments*: 

1.    No sulphur
2.    Sulphur applied as S liquid at 125 kg/ha SO3
3.    Sulphur applied as ammonium sulphate at 125 kg/ha SO3
*(nitrogen application will be adjusted based on the N content of the sulphur fertilizer used in each treatment)

For those of you that came along to the open day on 5 July you will have seen that there had at this stage been no effect on ground cover development and no visible difference between the treatments. It remains to be seen how this trail develops.

There will be opportunity to visit these plots at the SPot Farm walk on 1 September and of course the results will be made available to all levy payers after the trial is completed.

  

Ground cover in Straceys sulphur experiment (Russet Burbank, mean of eight replicates)

For more information contact: Jenny Bashford, Knowledge Exchange Manager, Jenny.Bashford@ahdb.org.uk,  07500 100 715

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