Nitrogen and sulphur fertilizer management for growing canola on sulphur sufficient soils

Abstract

. 2007. Nitrogen and sulphur fertilizer management for growing canola on sulphur sufficient soils. Can. J. Plant Sci. 87: 201-210. Canola is a crop that demands high nitrogen (N) and sulphur (S) inputs to achieve maximum seed yield. The practice of balancing these two nutrients by applying them in a fixed ratio has shown yield benefits on soils deficient in both these nutrients. A 9 site-year study was conducted between 2002 and 2004 to determine whether this practice is necessary for soils containing sufficient S levels. The practice was tested for both hybrid (HC) and open pollinated (OPC) canola cultivars by applying six rates of N (0, 40, 80, 120, 160 and 200 kg N ha -1 ) and supplementing N rates with S, so that three N:S ratios (1.5, 6 and 12 to 1) were achieved. Seed yield, protein and oil content responses of both HC and OPC cultivars were obtained primarily with N, with no evidence for a need of balancing this nutrient with S additions to achieve a ratio within those applied at this study. Hybrid canola cultivars overall yielded 23.7% more than OPC cultivars when they received the N application rate at which maximum yield of the OPC cultivars was obtained (120 kg N ha -1 ). Application of an additional 30 kg ha -1 to obtain maximum HC seed yield only resulted in an additional 1.5% yield advantage for the OPC. As N application rate was increased, small increases in seed protein levels (≈2.5%) were accompanied by a small reduction (≈2%) in seed oil content. Increased yield by HC compared with OPC canola reduces N residual fertility, hence, assessment of soil fertility status by soil testing after growing HC canola is a highly beneficial management practice. Our results indicate that the practice of balancing N and S to a fixed ratio is unnecessary and wasteful on canola grown on soils containing sufficient S. Le rendement grainier, la concentration de protéines et la teneur en huile des cultivars H et PL réagissent surtout aux engrais N, sans qu'il soit apparemment nécessaire d'équilibrer cet élément nutritif par un apport d'engrais S en vue d'obtenir un ratio situé dans la fourchette examinée. En général, les cultivars H donnent un rendement de 23,7 % supérieur à celui des cultivars PL avec la même quantité d'engrais que celle dont les cultivars PL ont besoin pour atteindre leur rendement maximal (120 kg de N par hectare). Appliquer 30 kg de N de plus par hectare aux cultivars PL comme on le ferait aux cultivars H pour qu'ils parviennent à leur rendement grainier maximal n'accroît leur rendement que de 1,5 %. Lorsqu'on augmente le taux d'application de N, la petite hausse de la concentration de protéines dans la graine (≈ 2,5 %) s'accompagne d'une légère baisse de la teneur en huile (≈ 2 %). Comparativement aux cultivars PL, la hausse du rendement des cultivars H réduit la fertilité résiduelle du N, de sorte qu'une analyse du sol s'avère une pratique très bénéfique après la culture de canola H. Les résultats de l'étude indiquent que vouloir équili-brer le N et le S selon des ratios établis pour cultiver...

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