STUDY ON FUNCTIONAL SULPHUR REQUIREMENTS FOR LEAF EXPANSION AND AS A CRITICAL VALUE FOR SULPHUR DEFICIENCY IN OILSEED RAPE

Sulphur(S) supply control to canola-double low oilseed rape (Brassica napus cv.Hyola) experiment was carried out in growth cabinets of phytotron to investigate effect of S stress on growth of the seedlirigs. The results indicated that leaf area and weight ratio (A/W) was one of the most sensitive parameters to S deficiency in oilseed rape. Therefore, the functional sulphur requirements for leaf expansion was obtained from A/W changes with S concentration. Functiorial sulphur requirements determined in this way was more sensitive and accurate than did the critical values determined in conventional one by correlation with plant or tissue dry matter (DM). For nutrients with low mobility, such as S. the young tissue must be affected first when there was a nutrient shortage, the young leaf blade was a good indicator to reflect nutrition status in plants but plant (or leaf blade) DM responded slowly and insensitively because the nutrient deficiency usually depressed leaf blade expansion but increased plant (leaf) DM. Therefore, shoot DM for response to S stress development usually gave it unsatisfled results for setting critical values, these results were correlated with relatively increasing in net assimilation rate (EA) and relative growth rate (RW) for S deficiency. The functional sulphur requirements determined by relative leaf expansion rate was 0. 32% while that determined by shoot DM was below 0. 1%. Furthermore, the response of leaf area or length could be seen approximately 10 days earlier than that of DM after reduced S supply.Functional sulphur requiremants can be used as a crllical value for diagriosis of S deficiency in oilseed rape.