THE SULPHUR STATUS OF EASTERN CANADIAN PRAIRIE SOILS: SULPHUR RESPONSE AND REQUIREMENTS OF ALFALFA (Medicago sativa L.), RAPE (Brassica napus L.) AND BARLEY (Hordeum vulgare L.)

Abstract

Alfalfa (Medicago sativa), rape (Brassica napus) and barley (Hordeum vulgare) were grown in a growth chamber with and without sulphur (S) on surface samples (0–15 cm) of 17 eastern Canadian prairie soils. The soil varied in pedological origin and were divided into three groups based on their total nitrogen:total sulphur (N:S) ratios. Herbage yield of alfalfa (full bud) and rape (flowering) were highly correlated (P < 0.01) with soil (N:S)s ratios and soil SO4-S, while for barley (shot blade) the relationships were significant [Formula: see text]. Herbage yields of the three crops were also significantly correlated [Formula: see text] with plant (N:S)p ratios. Soil (N:S) ratio was considered the best predictor of herbage yield because it is more stable over time than soil SO4-S and because plant (N:S)p ratio only indicates a need for future fertilization. The highest yields and S and N composition of plant tissues were obtained on soils with SO4-S concentrations greater than 12 mg kg−1 and an (N:S)s ratio of approximately 6. These soils had sufficient S to meet the requirements of all three crops. Addition of S had no effect on herbage yield but did increase S uptake. Results indicated that soils with (N:S)s ratio of 9 and SO4-S concentration of 7 mg kg−1, may have sufficient S to meet the requirement of barley but not alfalfa and rape. However, soils with higher (N:S)s ratios and lower SO4-S content were deficient in S for all crops. Barley was the most responsive to applied S of the three crops, although it had the lowest concentration of S (0.15 mg S g−1 dry herbage) and highest plant (N:S)p ratio (16) at its highest yield. Rape was more responsive to applied S than alfalfa but the concentration of S in the herbage of both crops at their highest yields were similar, 0.27 and 0.26 mg S g−1 dry herbage, respectively. Both crops also had lower (N:S)p ratios than barley at the highest yield (14 (alfalfa) and 12 (rape)), reflecting their greater S uptake. Key words: Plant-available S, soil (N:S)s ratio, plant (N:S)p ratio, plant uptake of S, plant uptake of N