Iron pyrites as sulphur fertilisers

Nitrogen and sulphur fractions were determined in grass and clover sepalates in two harvests (5 and 6) of a trial in which elemental sulphur (S), fine‐grained marcasite (Ma), and coarse‐grained pyrite (Py) were compared as sources of sulphur. The ratio N/S in the protein ((N/S p ) averaged 14.6 and 16.7 in the grass at harvests 5 and 6 respectively, and 17.8 and 19.1 in the clover, and wIthin each treatment group there was a tendency for higher (N/S) p ratios in treatments of lower S status. There was evidence of incomplete extraction of non‐protein S by a single hot‐ethanol treatment, and it was necessary to correct the protein S, so determined, by subtracting a reducible‐S fraction (obtained by direct Iohnson‐Nishita distillation of the protein material) to obtain a corrected figure for protein S. Even three ethanol extractions did not remove all the reducible S. Non‐protein N was poorly correlated with total N, and with total S, and there was no evidence of an increase in non‐protein N with increasing S deficiency. Nitrate N was very low in both grass and clover at both harvest dates. This contrasts with the usual behaviour of S‐deficient plants receiving nitrogenous fertilisers. Non‐protein organic S was significantly correlated with total S, but appeared to decrease with increasing S deficiency, despite increases in total S. The ratio non‐protein Ninon‐protein organic S appears to be a sensitive index of S deficiency.