Choosing a treatment to beat sulphur deficiencies
SULPHUR is a leading nutrient and set to become even more important. But treatments are not equal – applying elemental sulphur now could pay dividends over spring ammonium sulphate, claim experts.
"The deficiencies weve seen so far are just the beginning," says Eric Evans of Newcastle University. "Government is committed to cut sulphur dioxide emissions by industry even further, to 60% of the 1980 level by 2003, so sulphur deficiency is going to accelerate."
But soil type and organic matter levels are also important, he says. When all factors are combined the resulting deficiency map shows 33% of the UK is at high or medium risk of sulphur deficiency already – with arable areas worst affected. Projections for 2003 show 23% of the land at high risk and 27% at medium risk, accounting for virtually all arable areas.
Sugar beet is "coming more into the picture", and there are suggestions of a response in potatoes, notes Dr Evans. Falling sulphur levels in grain also threaten bread-making quality. "There is going to be tremendous demand for sulphur."
Mistakes are made
But coping with deficiency is not easy, as Canadian research agronomist Elston Solberg testifies. "Weve had sulphur deficiency in Canada for 30-40 years, but farmers still make mistakes."
His advice is to identify susceptible sites early and look carefully at sulphur release rates when choosing a product.
"By the time deficiency shows you are losing 30-40% yield. We want to catch it at 10-20%." To do that target coarse-textured, well-drained soils with low organic matter levels, he says.
Soil testing and tissue analysis can then help identify a shortage, but checking the nitrogen to sulphur ratio of grain from the preceding crop is a more practical approach, says Mr Solberg.
Howard Banks, head of agriculture for Tiger 90 sulphur pellet importer Stefes, agrees. "Treat once the N:S ratio exceeds 10-12:1 in cereals and 8:1 in oilseed rape," he says.
Long term trials in Alberta show elemental sulphur is then the best product. Its sulphur can not leach until soil microbes convert it to sulphate, ensuring sulphate is available throughout the growing season. Although heavy rain may wash some sulphate away, more sulphur is available for degrading, he explains.
That has been an advantage in Canada and is likely to be even more useful in the UK, where leaching is a greater worry, he comments.
However, microbe populations may be low at the outset. That can reduce availability in the first year, so an earlier treatment or slightly higher rate may be needed at first.
Early treatment is best
Trials in the UK confirm the picture, claims Mr Banks. Newcastle University work in 1994 showed an early April application of elemental sulphur as Tiger 90 was as effective as ammonium sulphate. "And that was a late application in a dry season, which would usually favour sulphate."
A Scottish Agronomy trial this year shows Tiger outperforming ammonium sulphate, while work at Cockle Park near Newcastle confirmed the value of applying elemental sulphur in the autumn rather than spring.
• Deficiencies set to worsen.
• Coarse, low organic matter, drained soils at most risk.
• Check N:S ratio of grain from prior crop and treat if over 12:1 in cereal or 8:1 for OSR.
• Elemental sulphur gives longer release than sulphate, cutting risk of leaching losses.
Sussing sulphur strategies (left to right): Howard Banks of Stefes, Dr Eric Evans of Newcastle University and Canadian agronomist Elston Solberg. All advocate autumn applications of elemental sulphur.