Changes to sulphur guidance recommended

Sulphur (S) experiments conducted on winter oilseed rape (WOSR) have revealed that current recommendations only require a small adjustment and not the significant uplift anticipated by some, reports AHDB.

The work also discovered that crops are able to use S from organic sources more efficiently than previously thought.

The findings will now be considered by the UK Partnership for Crop Nutrient Management – the body responsible for the AHDB Nutrient Management Guide (RB209).

The ADAS-led research investigated the current optimum S rate recommendation for WOSR and the S supply from organic materials.

Optimum S rates

WOSR S-response experiments were carried out at ten field sites (harvest years 2014 to 2017) during the project. Results from a further eight experiments, carried out between 2011 and 2013, were also analysed.

Ten of the 18 experiments showed a yield response to S fertiliser of between 0.1t/ha and 4.4t/ha. The economic optimum S rates at the sites varied between 30kg and 79kg SO3/ha. There was no evidence to suggest that modern, higher-yielding WOSR varieties required more fertiliser.

All of the sites that showed a yield response had light- or medium-textured soils (ie loamy sand, sandy loam or sandy clay loam soils).

Soil texture and winter rainfall was found to be a more reliable predictor of S deficiency than soil analysis or tissue testing.

The researchers suggested that S recommendations in RB209 be updated in line with the recommendations for cereals, which take both soil texture and winter rainfall into account.

As WOSR at some sites responded to a slightly higher S rate than in the current recommendations (50kg to 75kg SO3/ha), the researchers suggested the range be extended slightly – to 50kg to 80kg SO3/ha.

Dr Sajjad Awan, who manages nutrient research at AHDB, said: “The recommendations for sulphur use were first published in RB209 in 1994. Since then, deposition from the atmosphere has decreased dramatically and the yield potential of modern varieties has increased. The assumption has been that modern WOSR production needs much more sulphur than the official recommendations suggest. Our research, however, shows that this is not true and the current recommendations are not a million miles away from where they need to be.”

S supply from organic materials

Five of the S-response field experiments included additional organic material treatments.

The results showed that crops use S from organic sources more efficiently than previously thought. As a result, the researchers recommended that S-use efficiency values associated with autumn applications of organic materials be updated for WOSR and grassland – to 15 per cent for livestock manures (from 5 to 10 per cent) and to 25 per cent for biosolids (from 10 to 20 per cent).

The researchers also suggested that the S-use efficiency values associated with spring-applied slurry and biosolids be increased for all crops – from 35 per cent to 45 per cent, and 20 per cent to 35 per cent, respectively.

Sajjad said: “Previous AHDB-funded research determined how sulphur from organic materials contributes to winter wheat’s requirements. This research has now quantified the contribution to other crops. With around 65 per cent of farms in Britain applying organic materials, and with both autumn and spring applications making a valuable sulphur contribution, it means many farmers could now potentially reduce their inorganic fertiliser requirements.”