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Assessing sulfur adequacy in winter cereals

10 October 2011 | Categories: sullfur, sulphur, N:S ratio, grain, soil test

The incidence of low sulfur rates in grain and sulfur deficiency in winter cereal plants seems to have increased in the northern cereal belt in recent years.

The problem first appeared in barley crops on the southern Darling Downs in the early 1980s, usually as yellow, stunted, heavily diseased patches of barley in otherwise normal crops in late winter and early spring.

More recently, the hint of a more widespread sulfur problem has come from wheat grain  N:S results and reponses to inclusion of sulfur in fertiliser programmes .

One of the first signs of sulfur problems is a reduction in grain sulfur levels and a widening of the grain nitrogen : sulfur ratio.

The sulfur content of the grain is particularly important in bread and durum wheats because low grain sulfur (or nitrogen) can significantly reduce dough quality (elasiticity).

Along with this problem, affected crops  also appear to be  more susceptible to diseases, because the nitrate and sugar levels in the plant are raised by the inability of the plant to synthesis some amino acids, providing ideal conditions for spreading fungal diseases.

The risk of sulfur problems arises mainly where:

• double cropping is practiced
• crops are planted on shallow upland soils
• where the depth to a significant subsoil sulfur layer is 40 cm or greater
• in soils with low orgainic matter 
• following dry summers when mineralisation of organic matter have been limited

 

At the moment, there is a limited amount of data to interpret soil tests for sulfur in cereal crops. Of the two methods currently available (MCP and KCl40), both appears to be useable for northern grain crops the most important point being testing needs to include sampling to at least 50 cm.

If you suspect a sulfur problem in your crops,  it is not too late to confirm or dismiss your suspicions  by grain  analysis this season or soil anlayisis next autumn before starting out on a big sulfur fertilizer program.