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Fluid Journal : Fluid Journal 2005-2007
split application among years is especially evident when comparing 2005 (Figure 1) to 2004 (Figure 2). In 2005, a wetter year that was subject to significant early- season N losses, the advantages of split N applications are more fully illustrated. In 2004, which was characterized by cool growing- season conditions and a lower accumulation of "physiological days" suitable for crop growth, split application was not advantageous. The yield of marketable (greater than 3 oz) tubers was also assessed. In general, effects of N management on marketable yield were similar to those observed for total yield. In 2005, however, marketable yield was greater for the 4x split than for the other timing methods assessed, despite similar total yield in the 4x split and the preplant treatment (Figure 3). Contrasted to 2005, the 4x split in 2004 resulted in a lower marketable yield than the preplant treatment, and the 2x split was intermediate. Although soil NO3-N levels were relatively low at experimental sites in the spring prior to crop establishment (ranging among sites from 36 to 54 kg NO3-N ha-1 to 60 cm), and only a small amount of N fertilizer (10 to 21 kg N ha-1) was applied to the control treatment, total tuber yield in control treatments was usually 84 to 91 percent in the highest yielding treatment (Figure 1). These findings and previous studies in Manitoba have similarly pointed to the potential for significant contributions of N in irrigated potato production systems through mineralization of soil organic matter during the growing season. Specific gravity was strongly influenced by N fertilizer management. Increasing N rate resulted in a significant linear decline in specific gravity in three of four site-years. Timing of N application 0 100 200 300 400 500 0 75 150 225 Fertilizer N (kg N ha-1) Marketable yield (cwt ac-1) Preplant 2x split 4x split Figure 3. Effect of N fertilizer application rate and timing on marketable tuber yield at Carberry, 2005. Wt >12 oz Wt 10-12 oz Wt 6-10 oz Wt 3-6oz Wt <3oz 0 100 200 300 400 500 600 Control 75 pre 150 pre 225 pre75 split 2x 150 split 2x 225 split 2x 75 split 4x 150 split 4x 225 split 4x Tuber yield (cwt ac-1 ) 0 50 100 150 200 250 300 350 400 450 Control 75 pre 150 pre 225 pre7 5 split 2x 150 split 2x 225 split 2x 75 split 4x 150 split 4x 225 split 4x Tuber yield (cwt ac-1 ) Wt >12 oz Wt 10-12 oz Wt 6-10 oz Wt 3-6oz Wt <3oz Figure 2. Effect of N fertilizer application rate and timing on yield of various tuber size fractions at Winkler, 2004. Figure 1. Effect of N fertilizer application rate and timing on yield of various tuber size fractions at Carberry, 2005. 10 Fluid Journal SPRING 2007
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