Sulphur is a critical plant nutrient which often gets forgotten by our narrow emphasis on NPK. Many Irish soils are deficient in Sulphur yet having adequate amounts is important for nitrogen use efficiency and will have a big impact on yield and quality. Plants which have a high sulphur requirement include oilseed rape, brassicas, onions, leeks as well as grassland. The main symptom of S deficiency is a leaf yellowing similar to that of N deficiency but with younger leaves suffering more.
Adding larger amounts of sulphur is also one of the most effective ways to lower soil pH. The pH is lowered as a result of soil bacteria converting the Sulphur into Sulphuric acid. This is a slow biological process and not a rapid chemical reaction. It takes places when the bacteria are active which is when the soil is moist and warm. The soil temperature needs to be above 13C° so a Spring application and incorporation work best. Elemental sulphur is approved for use on organic holdings.
Granular Elemental Sulphur
- 87% Sulphur/13% Bentonite.
- Sulphur is an essential plant nutrient necessary for plant growth and improves the use efficiency of other essential plant nutrients, particularly nitrogen and phosphorus.
- Lowers pH in alkaline soils.
- Also useful as a soil amendment around acid loving plants such as blueberries, azaleas and rhododendrons.
- Granulated form is easier to handle and provides a less leachable source for a continuous supply of sulphur.
- Can be applied with a spreader.
Applying Elemental Sulphur
- Soil tests are an unreliable indication of sulphur as most of the S in soils is bound up in organic matter.
- Base application on the crops demands rather than trying to build up soil levels of sulphur.
- Sandy soils which are free draining are most susceptible to S deficiency.
- Do NOT exceed more than two applications per year.
- Do not apply at temperatures 24° C or higher.
- Keep away from flames or sparks.
- Sulphur may irritate nasal passages, skin and eyes - always wear protective clothing when handling sulphur.
General Application Rates:
- Silage - 25kg/ha per cut
- Grazing - 25kg/ha per season
- Vegetables - 50kg/ha applied in Spring
- Potatoes - 25-40kg/ha
Using Sulphur to Adjust pH:
Much larger quantities are required if sulphur is being used to lower pH. Changes in soil pH occur slowly so it may take a couple of months or longer to see a difference. The amount of sulphur required is dependent on soil texture. Clay and organic matter act as a buffer, absorbing and releasing mineral ions. Relatively little sulphur is needed on sands, whereas soils high in clay or organic matter require much more. It is important to apply and incorporate sulphur at least a year before planting. This allows the sulphur time to react and lower the soil pH before planting.
As a rule of thumb, to lower pH by one point broadcast approximately 5kg per 100 m2 and work into the soil. (We recommend a soil test to determine actual rates). Surface-applied sulphur provides the same pH reduction as incorporated material but takes longer. Check soil pH again before planting and apply additional sulphur if needed. When large amounts are needed spread the application out over several years.