Diagnosing sulfur deficiency in field-grown oilseed rape (Brassica napus L.) and wheat ( Triticum aestivum L.)

The effects of increasing sulfur applications on field-grown oilseed rape (Brassica napus L.) and wheat (Triticum aestivum L.) were investigated in 1998 and 1999, and the critical values and efficiency of several diagnostic indicators for S deficiency were determined. Critical values for leaf concentrations of total S, sulfate and glutathione changed over time and were not suitable for diagnosing S deficiency early in the growth season. The N:S ratio was more reliable but involved two analytical measurements. A practical and reliable indicator for S deficiency was the malate:sulfate peak area ratio as measured by ion chromatography, which required only a single analysis and was independent of the time of sampling or calibration of the samples. A malate:sulfate ratio ≤ 1 indicated S sufficiency at the time of sampling, whereas a ratio > 1 suggested S deficiency at the time of sampling. The malate:sulfate ratio was reliable at growth stage 3.6–3.7 (flower stalks extending to first flowers yellow) for oilseed rape and at growth stage 22–25 (main stem and 2–5 tillers) for wheat, which was sufficiently early in the growth season to apply remedial sulfur fertilizer, if necessary. This revised version was published online in June 2006 with corrections to the Cover Date.