Testing times for sulphur application
Leaf tissue analysis is still the best way to assess if the crop is deficient in sulphur, advises Dr Lizzie Sagoo of ADAS.
She told Syngenta iOSR growers that soil type and any history of sulphur deficiency in other crops in the field or farm will give a good guide as to likely risk of deficiency, but if you want to test your OSR crop, we’d recommend the malate: sulphate tissue test.
"The malate:sulphate ratio test could give a good indication of potential issues, but growers need to take care with the timing of sampling," advised Lizzie.
“The key is to wait until the plant is actively growing and taking up available S from the soil, typically at the beginning of stem extension," advocated Lizzie (below), "if the leaf is taken too early it could indicate plants are less deficient than will be the case."
"However, it does need to be done in time to take corrective action before the crop is stressed by sulphur deficiency.”
Growers can also soil sample to highlight possible problems, with results of less than 10 mg/kg S of topsoil indicating potential deficiency, but Lizzie went on to explain: “Our experience is that soil analysis is less reliable than tissue analysis and I wouldn’t advise farmers to rely on soil analysis alone to assess their risk of deficiency.”
Visible symptoms, including yellowing growth, stunted plants and pale flowers (pictured at top of page, left untreated vs S fertiliser applied. Image copyright: ADAS) all indicate sulphur deficiency, but by the time they show most the damage to yield would have already occurred.
ADAS sulphur fetiliser trials have also looked at the positive contribution of sulphur supply from organic manures - both farmyard and biosolids.
Lizzie reported stronger autumn growth of oilseed rape would appear to be better at utilising the nutrient value of applications ahead of the crop, compared to cereal crops when much of the sulphur value appeared to be lost over the winter.
"Most organic manures can contribute towards the OSR crop’s sulphur requirement in the first season after application and should be factored into fertiliser recommendations," she advised.
However there is no evidence of the residual sulphur availability in the second year after application, so growers should stick to the recommended fertiliser application rates.
Records of sulphur inputs on UK farms has showed a steady rise through the 1990's to now stand at an average around 90 kg/ha - a level that has been evaluated in a series of ADAS trials. Read Dr Lizzie Sagoo's recommendations here.