Sulfur deficiency
A nutrient shortage that makes whole plants, especially the youngest leaves, pale yellow-green, and is often mistaken for nitrogen deficiency.
Also known as: Sulphur deficiency
Symptoms and identification
Young leaves turn evenly pale green to yellow, including the veins, while older leaves stay greener. Plants are small, stems are thin and woody, and brassicas and onions grow slowly with poor flavour.
Causes
Sulfur is low in light sandy soils, soils low in organic matter and soils that get little rainfall-borne sulfur because air pollution has cleaned up. Heavy cropping of brassicas and onions uses a lot.
Organic treatment
Apply compost, manure or gypsum, which release sulfur slowly as they break down. Keep soil moist, as roots take up sulfur as sulfate dissolved in water.
Prevention
Add compost or well-rotted manure every year and use fertilisers that contain sulfate, such as ammonium sulphate or gypsum, where crops are hungry for it.
Chemical treatment (use with care)
Use a fertiliser containing sulphate, such as ammonium sulphate, potassium sulphate or Epsom salts for some crops, following the label rates.