Autumn sulphur under question
IS autumn-applied sulphur worthwhile? That is the question being asked as evidence from HGCA-funded research highlights the significance of winter rainfall.
A key uncertainty is how much deficiency-correcting sulphur from autumn-spread pellets is left for crops to use after over-winter leaching, explains researcher Paul Withers of ADAS Bridgets. "My opinion is that farmers should apply sulphur just before stem extension, which is when problems occur."
Richard Martin of ICI Fertilisers, which supplies sulphur-containing fertiliser for spring use, agrees. Much of the research on slow release autumn products has been carried out in the USA, where winters are much colder and there is less leaching than in the UK, he says.
But Howard Banks for sulphur pellet supplier Stefes, which is funding a joint HGCA study at IACR-Rothamsted, stands by current recommendations. "We are also funding work in Germany and France which is giving us much more confidence in the product. We get better responses from winter application."
The sulphur in products like Tiger 90 reaches crops through two processes – physical and biological, he explains. The latter, which provides leachable sulphate, takes place only when soils warm up in the spring. Initial results from the Rothamsted work are favourable, he claims.
"The grey area is the speed of the conversion process." *