Effectiveness of seed-soaked Cu, autumn- versus spring-applied Cu, and Cu-treated P fertilizer on seed yield of wheat and residual nitrate-N for a Cu-deficient soil

Three field experiments were conducted from 2005 to 2007 to determine the effects of seed-soaking in Cu EDTA liquid, autumn versus spring application of granular Cu sulphate, and granular Cu-treated monoammonium phosphate (MAP) fertilizer on seed yield and Cu uptake of wheat, and residual nitrate-N in the soil profile on a Cu-deficient Dark Gray Luvisol (Boralf) sandy loam near Porcupine Plain, Saskatchewan, Canada. In exp. 1, seed soaked in Cu EDTA liquid at 0.04 to 0.16 kg Cu ha -1 increased seed yield substantially, in spite of a significant reduction in plant emergence in most cases. But, seed yield increases from the seed soaked in Cu EDTA liquid were lower compared with foliar-applied Cu EDTA liquid at 0.50 to 1.00 kg Cu ha -1 , or compared with surface spray-broadcast and incorporation of Cu EDTA liquid into soil in spring prior to seeding at 4.0 kg Cu ha -1 . Seed yield trend was two foliar applications of Cu EDTA liquid > soil surface spray-broadcast and incorporated Cu EDTA liquid > one foliar application of Cu EDTA liquid > seed-soaked Cu EDTA liquid. In exp. 2, for granular Cu sulphate in the first year, only previous autumn application increased seed yield significantly when applied at 4.0 kg ha -1 . For spring application, seed yield was highest when solution Cu EDTA at 4.0 kg ha -1 was spray-broadcast on the soil surface and incorporated into soil prior to seeding. In exp. 3, application of granular Cu-treated MAP fertilizer had no significant effect on seed yield. The Cu uptake by seed usually followed`the same trends as seed yield. In all experiments, the partial factor productivity (seed yield per unit of nutrient applied) was much higher when N was applied in combination with Cu (15.3 to 29.8 kg seed kg -1 applied N ha -1 ) compared with N alone (5.7 to 7.7 kg seed kg -1 applied N ha -1 ). In exp. 1, the amounts of residual nitrate-N in the 0-90 cm soil profile after three annual N fertilizer applications were 3.3 to 4.0 times higher in the zero-Cu control than in the Cu fertilizer treatments. Overall, seed yields of wheat were highest with two foliar applications of Cu at low rates, or with soil spray/broadcast and incorporation of solution Cu in spring at a relatively high rate, which is also expected to have long-term residual effects on crop yield. For granular Cu sulphate, the results indicated that deficiency of Cu in wheat can be corrected by surface-broadcast application at a relatively high rate in the previous autumn, followed by its incorporation into soil in the spring at seeding. The results also indicate that by soaking wheat seed in Cu EDTA solution at a very low rate, Cu deficiency in wheat can be prevented and seed yield increased, but less than the other Cu treatments. Accumulation and downward movement of residual nitrate-N in the soil profile can be minimized by preventing Cu deficiency in wheat crop with combined application of Cu and N fertilizers. Key words: Application time, Cu source, foliar application, granular Cu, growth stage, placement method, rate of Cu, seed-soaked Cu, soil incorporation, solution Cu

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