Balanced nutrition shown by nitrogen:sulphur ratios
November 2025
The majority of the nitrogen and sulphur in crops (other than the Brassicae, such as oilseed rape, cabbage, kale etc) is in combination in proteins, and as with most animal proteins the ratio of N to S (N:S) in plants is fairly consistently around 12:1. This close relationship between N and S can be illustrated using a French data-set that analysed the crops for the patterns of nitrogen and sulphur uptakes. In the figures the accumulation over the season of sulphur (as SO3) is shown by the red lines in the two charts, for wheat and potatoes. The two blue lines indicate an SO3 content which has been calculated from the measured N content, assuming a 12:1 N:S ratio. This would mean that for every 12 kg of N in the crop it would also contain 1 kg of S, or 2.5 kg of SO3. The fact that the blue and red lines are well aligned supports the principle that the sulphur requirement of these crops is closely related to their need for nitrogen.
It is likely that the necessary sulphur requirement can be predicted for many crops as being approximately one twelfth of their nitrogen requirement. This concept would still apply in principle to legumes, although the amount of ‘applied’ nitrogen is not known! Clearly brassicas have a much greater sulphur requirement due to the non-protein glucosinolates which contain S, and thus have a closer N:S ratio.
