Winter oilseed rape grown on light or shallow soils, in particular, could profit from more sulphur than indicated by the RB209 fertiliser manual, according to new research.
Mainly undertaken in Hampshire, Wiltshire and Dorset, the trials show yield and margin responses from applications of up to 225kg/ha of SO3 (90kg/ha S). The company believes it underlines both the extent to which lack of sulphur is becoming an issue in modern rape nutrition and the value of extra applications in boosting the efficiency of applied nitrogen.
“We’ve recorded yield increases of around 0.2t/ha for every extra 75kg/ha SO3 (30kg/ha S) added at the same nitrogen input,” reports Agrii’s west regional technical advisor, Gary Bosley. “And, like our parallel work with wheat, the response is clearly linked to N level.
“As a rule, tripling SO3 applications from a fairly normal 75 kg/ha to 225kg/ha has added a good 0.5 t/ha to yields. But we’ve seen responses of nearer 0.7 t/ha at higher levels of N application compared with about 0.2t/ha at lower levels.
“This is hardly surprising given the close relationship between nitrogen and sulphur in plant nutrition,” he observes.
“We know OSR requires about 16kg of sulphur for every 1t of seed yield, which equates to 80kg S for a 5t/ha crop. Under these circumstances, annual applications of less than half this level are unlikely to be able to sustain today’s 4t/ha plus crops. Unless, that is, significant sulphur contributions are available from soil organic matter or, as in the past, through atmospheric deposition.”
On shallow chalk and low organic matter soils, at least, Agrii crop nutrition technical manager David Langton sees significant increases in sulphur fertilisation as an important piece in the high-yielding winter OSR management jigsaw.
He also feels higher than RB209 levels of sulphur should be considered in other situations, particularly where higher nitrogen rates are being applied.
“We recommend applying up to 200kg SO3 in higher-risk situations. These are primarily higher-yielding crops, light (leachable) soils, where overwinter rainfall has been high, organic matter levels are low or poor mineralisation of organic S is likely. Of course, it’s important to appreciate that, like nitrogen, sulphur accumulates in the crop. So higher GAIs will reduce the need for spring sulphur as well as nitrogen.”