Monitoring of grain samples from wintercereal variety trials across Agriis principal northern England and Scotland R&Dsites last season suggests many high yielding crops, in particular, may stillnot be receiving sufficient sulphur in their main spring top dressings.
Nitrogen and sulphur analyses from 11 winter wheat and six winter barley trialsrevealed higher than ideal N:S ratios in the grain in many varieties at mostsites, indicating insufficient levels of sulphur for the greatest productivity;and this despite applications comfortably in excess of RB209 recommendations inalmost half the cases.
Historic grain N:S ratios clearly dont have the immediacy of current seasontissue analyses, agreed Agrii northern R&D manager, Jim Carswellresponsible for the monitoring. But as a benchmark of past success inachieving the right balance of the two nutrients I see them as a valuableelement in a risk assessment-based approach to sulphur nutrition. Especially astissue analyses merely provide a snapshot on the day and depend on accuratesampling at the right time.
Most of the grain N:S ratios we recorded across our trial sites last seasonwere, for instance, higher than the 17:1 indicative of sulphur deficiency inHGCA work, he reported. The ratios were particularly high and sulphurlevels correspondingly less adequate with higher yielding feed wheats andsix-row barleys. This suggests these crops could profit from greater attentionto sulphur nutrition than most.
We also saw clear differences between varieties under the same fertiliser regimesthat could usefully be taken into account in fine-tuning sulphur applicationsto greatest effect, rather than merely working to the general RB209 guidelinesof 25-50 kg SO3/ha in the early spring.
The findings are especially interestinggiven the relatively high levels of sulphur applied to many of the Agrii wheatand barley trials and the fact that some of the greatest imbalances revealed bygrain analysis were in crops receiving the highest relative levels offertiliser sulphur to nitrogen.
As well as variety, application timingis clearly a significant issue here, reasoned Jim Carswell. This was reallyhighlighted in our Bishop Burton wheat plots which showed the greatest across-the-boardsulphur imbalances with grain N:S ratios ranging from 19:1 to 24:1 dependingon variety despite receiving 228 kg/ha of SO3 and just 169 kg/haof N over the season.
In this case, the key was almost certainly the fact that to challenge thevarieties here they had approximately two thirds of their nitrogen and sulphurin early June rather than from March. While they were able to utilise the late Neffectively, the result underlines the importance of applying sulphur earlierin the growing season.
Jim Carswell recommends including most of the sulphur with the first two ofthis springs three nitrogen splits, using a 26:0:0:35 or 27:0:0:30 compound oreither poly-sulphate or kieserite to balance straight N. On lighter, free-draining, moresulphur-responsive soils he sees little and often application as especiallyvaluable given relatively high leaching risks.
For higher yielding feed wheats and six row barleys, in particular, he believestheres a serious case for higher levels of sulphur application than have beenthe case in many crops to date not least because such a small yield response isall thats needed to cover its cost and annual sulphur deposition is known tobe significantly below crop offtake in many parts of the country.
Id also suggest getting grain N:S analyses done on key varieties and fields thisharvest as the basis for future planning, Jim Carswell added. Intrigued byour work, one grower I know tested his stored 2014 grain and was startled tofind it had a 26:1 N:S ratio. He had absolutely no idea his crop sulphur statuswas so inadequate. Having discovered it, hes upping his applications thisspring to ensure a more productive balance this time around.
For our part, were developing and extending our own grain N:S analyses fromtrials this season to explore regional and varietal differences in greaterdetail so we can give our agronomist and grower teams better guidance on improvingthis important element of their crop management.