Record sulphur famine set to dent crop yields
By Andrew Swallow
SULPHUR deficiency seems set to slash the yield of some crops this year after severe winter leaching and an unprecedented drop in deposition levels.
Planning sulphur into next years fertiliser requirements is now a must, says Morley Agricultural Consultants Stephen Keach.
"It has got to the stage where if you are not using sulphur fertiliser then you need a very good reason not to be. Some of the deficiency symptoms this year are the worst I have seen," he says.
Widespread pollination problems are already being linked to sulphur shortfalls in oilseed rape (Arable, June 29) and some cereals are showing signs of a shortage. Classic symptoms are pale, stunted plants, but there is a danger growers will blame soil structure problems instead, he warns.
"It is easy to confuse and does occur in patches tending to follow soil types." Tissue tests during normal growing conditions, not drought, should be used to confirm suspicions.
Lighter soils tend to be most deficient, as sulphur, like nitrogen, is leached in wet weather. Organic matter binds it up, releasing reserves through mineralisation when soils warm up.
For cost and uptake reasons applications of sulphur should be made as a fertiliser containing ammonium sulphate, says Mr Keach (see table).
But, as it is easily leached, timings need to coincide with crop growth as closely as possible. "This year early applications could have been leached before crops really started to grow, so there may be a need to review timings. On lighter soils there is considerable merit in using a lower sulphur concentration and using it more frequently."
If going only once with a sulphur product on cereals, then waiting until GS31 when the crop is really starting to grow would reduce the risk of leaching, he says.
In previous seasons yield responses of over 0.5t/ha (4cwt/acre) to sulphur on cereals have been achieved at Morley, despite limited visual symptoms of deficiency, notes Mr Keach.
This year stunting on a winter barley trial where no sulphur has been applied suggests responses could exceed that, he says.
• Tissue test stunted crops.
• Plan next years need.
• Use ammonium sulphate.
• Consider later timing.
Sulphur on cereals
Sulphur application Date Cost (£/ha) Total S % N:S ratio
Nil 0.30 10.5
Elemental S (to soil) Mar 17 14.48 0.32 10.9
Elemental S (to crop) Apr 9 11.68 0.33 10.2
Ammonium Sulphate Mar 17 6.98 0.44 8.1
Ammonium Sulphate May 2 6.98 0.63 5.5
Source: HGCA. Higher % S figure, and lower N:S figure better.
S or SO3?
Confusion can reign when sulphur is discussed. Is it S or SO3? Manufacturers of elemental sulphur products tend to talk S content while fertiliser manufacturers legally must state SO3 content on the bag.
IACR-Rothamsteds Steve McGrath says crop needs are referred to in terms of elemental sulphur and for sulphate fertiliser calculations growers must multiply by 2.5. So, in order to deliver 18kg/ha of sulphur 50kg/ha of sulphate is needed which, in a 60% sulphate product such as ammonium sulphate means spreading 83.3kg/ha of fertiliser.