Critical values for sulfur in young plants of oilseed rape (Brassica napus L.) determined with reference to dry weight, leaf area and specific leaf weight

Abstract

Oilseed rape has a high requirement for sulfur (S) compared with cereals and many other species, and when soil S supplies are low it is one of the first crops to show deficiency. Timely diagnosis of S deficiency is important so that fertiliser can be applied to avoid a reduction in yield. The concentration of S in plant tissue is commonly used as an aid in diagnosis of deficiency, and the establishment of critical concentration values is an essential prerequisite for the interpretation of leaf analysis. We studied shoot dry weight, leaf area and specific leaf weight following the withdrawal of S from the nutrient solution for their sensitivity to S deficiency for establishing critical concentrations in oilseed rape. Dry weight was the least sensitive with differences between adequately and inadequately supplied plants not reaching significance for over 20 days. Leaf area differences became significant after 13 days. Specific leaf weight was the most sensitive measure with differences showing after 10 days. Specific leaf weight was less than 30 g m-2 in S-sufficient leaves and over 40 g m-2 in S-deficient leaves after 20 days. Specific leaf weight increased in fully expanded leaves and in expanding leaves due to S deficiency. Critical S values were similar when either leaf area or specific leaf weight was used for estimating them, and these values were higher than values derived using dry weight. However, all the critical values estimated using the present procedure were lower than those derived empirically in field studies, and the empirical values would be preferred for decision making in fertiliser programs for crops.