Historically, in the UK sulphur was deposited on land from the atmosphere in quantities which were adequate for our crops, but today very little sulphur lands on our fields. As a result, applications of sulphur to crops has become an essential part of nutrient management planning.
Sulphur In The Soil
Sulphur in the soil acts in a similar way to nitrogen. It arises naturally from the breakdown of organic matter, and to some extent from soil minerals. Soils which are organic, or heavy textured are more able to supply adequate sulphur than light and inorganic soils.
The organic sulphur compounds are broken down to inorganic forms, which are then useful to the plant.
Sulphur In The Plant
The major role of sulphur in all plants is in support of nitrogen in protein production. In grass, sulphur is probably more important for improving the quality of grazing and silage, in terms of protein, than the yield increase achieved.
Deficiency symptoms in cereals, grass and brassicas show up in the younger leaves first. Symptoms are a pale yellow appearance (chlorosis) and, later on, stunting. Symptoms are easily missed, or confused with nitrogen deficiency , and may not be noticed at all, especially in cereals and grass.
Application Of Sulphur
In short, sulphur should be applied to most multi cut grass silage, grown on mineral soils. For other situations, heavier and organic soils are less likely to need sulphur, and lighter soils and high rainfall areas are more likely to need it.
For nutrient purposes, the crop requirement for sulphur is expressed as kg SO3/ha. Where sulphur is needed, the quantities to be applied and timings are as shown below:
- Grass for silage: 40 kg SO3/ha prior to each cut. NB second and subsequent cuts are the most sensitive.
- Grass for grazing: 20 – 30 kg SO3/ha in spring and again mid season.
Peter Hoey, The Potash Development Association
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