Sulphur
Sulphur has an important role in the formation of proteins an dis essential for the production of chlorophyll. Crops that have a high N requirement must have adequate S to optimise N utilisation and protein synthesis.
Sulphur deficiency in oat crops is rare in WA, mainly because of the widespread use of superphosphate (11% S). As with N and P, most of the S in the soil is in organic form. Soils with low amounts of organic matter are prone to S deficiency. Sulphur in organic matter must be mineralised to sulphate before being taken up by roots. Sulphate is mobile in soils and can be leached out of the rooting zone during winter. Deficiencies therefore most often occur in wetter years. On duplex soils, deficiency symptoms may be only temporary as roots grow into the deeper soil layers where more S is available.
Sulphur deficiency is expected to increase in oat crops in the future as more compound fertilisers containing lower S are used in oat production. Hay production, particularly on sandy soils is expected to increase the risk of S deficiency as hay crops remove about 1.5kg S/ha per tonne of hay.
A soil test value of less than 10mg/kg in the soil surface (0-10cm) may indicate likely S deficiency. However, S in the soil frequently increases down the soil profile, so knowledge of the distribution of S in the soil profile is required. This may involve deeper soil sampling to know the Ss uppl in the soil. Applying P as superphosphate and compound fertilisers that applies S at 5-10kg/ha can avoid S deficiency.
S deficiency symptoms
The youngest leaves of S deficient plants are pale green and then pale yellow across the whole leaf (no striping). Under severe deficiency the entire plant becomes a lemon-yellow colour with red stems.