A Preliminary Testing of Plant Analysis Procedures for the Assessment of the Sulfur Status of Oilseed Rape

The effects of sulfur and nitrogen supply on the distribution of sulfur in oilseed rape (Brassica napus cv. Oro) grown in a sulfur-deficient soil in a glasshouse were examined to provide basic information for the development of a diagnostic test for sulfur status. Even though the traditional diagnostic indices (total sulfur and sulfate concentration) were directly related to sulfur supply and exhibited wide ranges in values between deficient and non-deficient tissue, they suffered a number of drawbacks in the case of oilseed rape. The shape of the yield/composition relationship precludes the use of either total nitrogen to total sulfur ratio or the proportion of the total sulfur present as sulfate in very young plants as indices for predicting the adequacy of sulfur supply up to first seed set. However, either index looked promising at 59 days from sowing, especially if specific plant parts were selected for analysis. For diagnosis of the current sulfur status the proportion of the total sulfur present as sulfate gave a good indication at each sampling date, and the critical value for the shoots was relatively stable with respect to age and nitrogen supply. Total nitrogen to total sulfur ratio was satisfactory as a diagnostic index for the 59-day-old plants only. Whilst the relationships established between the indices on one hand, and plant part, age and nitrogen supply on the other, should also apply in the field environment, the magnitude of the critical ratios requires confirmation for practical application.