February 25, 2015
Grain monitoring highlights continuing cereal Sulphur shortage
Monitoring of grain samples from winter cereal variety trials across Agrii’s principal northern England & Scotland R&D sites last season suggests many high yielding crops, in particular, may still not be receiving sufficient sulphur in their main spring top dressings.
Nitrogen and sulphur analyses from 11 winter wheat and six winter barley trials revealed higher than ideal N:S ratios in the grain in many varieties at most sites, indicating insufficient levels of sulphur for the greatest productivity; and this despite applications comfortably in excess of RB209 recommendations in almost half the cases.
“Historic grain N:S ratios clearly don’t have the immediacy of current season tissue analyses,” agreed Agrii northern R&D manager, Jim Carswell responsible for the monitoring. “But as a benchmark of past success in achieving the right balance of the two nutrients I see them as a valuable element in a risk assessment-based approach to sulphur nutrition. Especially as tissue analyses merely provide a snapshot ‘on the day’ and depend on accurate sampling at the right time.
“Most of the grain N:S ratios we recorded across our trial sites last season were, for instance, higher than the 17:1 indicative of sulphur deficiency in HGCA work,” he reported. “The ratios were particularly high – and sulphur levels correspondingly less adequate – with higher yielding feed wheats and six-row barleys. This suggests these crops could profit from greater attention to sulphur nutrition than most.
“We also saw clear differences between varieties under the same fertiliser regimes that could usefully be taken into account in fine-tuning sulphur applications to greatest effect, rather than merely working to the general RB209 guidelines of 25-50 kg SO3/ha in the early spring.”
The findings are especially interesting given the relatively high levels of sulphur applied to many of the Agrii wheat and barley trials and the fact that some of the greatest imbalances revealed by grain analysis were in crops receiving the highest relative levels of fertiliser sulphur to nitrogen.
“As well as variety, application timing is clearly a significant issue here,” reasoned Jim Carswell. “This was really highlighted in our Bishop Burton wheat plots which showed the greatest across-the-board sulphur imbalances – with grain N:S ratios ranging from 19:1 to 24:1 depending on variety – despite receiving 228 kg/ha of SO3 and just 169 kg/ha of N over the season.
“In this case, the key was almost certainly the fact that to challenge the varieties here they had approximately two thirds of their nitrogen and sulphur in early June rather than from March. While they were able to utilise the late N effectively, the result underlines the importance of applying sulphur earlier in the growing season.”
Jim Carswell recommends including most of the sulphur with the first two of this spring’s three nitrogen splits, using a 26:0:0:35 or 27:0:0:30 compound or either poly-sulphate or kieserite to balance straight N. On lighter, free-draining, more sulphur-responsive soils he sees little and often application as especially valuable given relatively high leaching risks.
For higher yielding feed wheats and six row barleys, in particular, he believes there’s a serious case for higher levels of sulphur application than have been the case in many crops to date – not least because such a small yield response is all that’s needed to cover its cost and annual sulphur deposition is known to be significantly below crop offtake in many parts of the country.
“I’d also suggest getting grain N:S analyses done on key varieties and fields this harvest as the basis for future planning,” Jim Carswell added. “Intrigued by our work, one grower I know tested his stored 2014 grain and was startled to find it had a 26:1 N:S ratio. He had absolutely no idea his crop sulphur status was so inadequate. Having discovered it, he’s upping his applications this spring to ensure a more productive balance this time around.
“For our part, we’re developing and extending our own grain N:S analyses from trials this season to explore regional and varietal differences in greater detail so we can give our agronomist and grower teams better guidance on improving this important element of their crop management.”