The effect of canola cultivar on water extraction and nitrogen and sulphur uptake

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Riekman, Marla Rae
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The objective of this study was to assess the mechanism that leads to enhanced uptake of N and S by a hybrid canola cultivar. Two canola cultivars, one hybrid (45H21) and one open-pollinated (Conquest) were grown at a single location near Rosebank, MB during the 2003 growing season to study the impact of canola cultivar and S fertilization on the uptake of water, N and S from the soil. The experimental design was a Randomized Complete Block where each cultivar was exposed to three fertilizer treatments: a control, 160 kg N ha-1: 0 kg S ha-1, and 160 kg N ha-1: 27 kg S ha-1. Soil and plant N and S concentrations were measured at midseason and maturity to determine the uptake of N and S by each cultivar. Soil moisture content was monitored throughout the growing season to study the activity of the canola roots. As well, soil cores were removed at midseason to determine the difference in rooting depth by each cultivar. The year following the canola crop experiment, AC Barrie spring wheat was seeded to the canola stubble without N fertilizer to study the effect of N and S uptake by each canola cultivar on a subsequent crop. Biomass was greatest for the hybrid canola cultivar at both sample periods. The concentration of N and S in the canola tissue at midseason was higher in the open-pollinated cultivar, which offset the biomass difference; therefore, the total N and S accumulated by each cultivar was not statistically different. At maturity, the difference in tissue concentrations was seen for S only. The addition of fertilizer caused an increase in biomass proeduction as well as a significant increase in N accumulation at midseason and maturity, and an increase in S accumulation at maturity only. Seed yield was highest for the hybrid cultivar and increased with fertilizer application for both cultivars. There was no interaction between cultivar and fertilizer treatment, indicating that each cultivar responded similarly to fertilizer addition. There was no significant difference in rooting depth between the two cultivars; however, the hybrid cultivar removed 58 mm more water than the open-pollinated cultivar over the 10 to 110 cm soil depth during the growing season, for the N plus S fertilizer treatment only. The difference in root activity may be attributed to the greater biomass of the hybrid canola, leading to higher rates of transpiration. Water use efficiency (WUE) was greater for the hybrid canola cultivar due primarily to the higher seed yield of this cultivar. The biomass accumulated by the wheat seeded onto the open-polliinated canola stubble waas numerically greater than that on the hybrid stubble, but this was significant for the midseason sampling period only. Biomass accumulation and total recovery (biomass and soil) of N and S by the wheat seeded onto the open-pollinated stubble was numerically greater, but not significantly so. Again, there was no interaction between cultivar and fertilizer treatment on either accumulation or recovery of N and S by the wheat crop.