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Fluid Journal : Fluid Journal 2005-2007
SPRING 2007 Fluid Journal 9 SUMMARY Nitrogen (N) application often increased total and marketable yield (greater than 3 oz) of irrigated potato compared to the control treatment for soils with low-to-medium soil test NO3 levels. Control treatments receiving negligible amounts of N fertilizer typically yielded between about 85 to 90 percent of the highest N treatment, suggesting that mineralization of soil organic N may contribute significantly to the plant-available N supply in irrigated potato systems in Manitoba. Split-applying N fertilizer did not generally result in a yield benefit, except in 2005. In 2005, timing of N application influenced tuber yield and size distribution, with the 4x split producing a higher marketable yield than the other treatments. In that year, total tuber yield was also numerically the highest for the 4x split, but did not differ significantly from the treatment in which all the N fertilizer was applied preplant. The general trend in 2005 was for larger tubers where N applications had been split-applied. Above-average precipitation early in the growing season of 2005 likely contributed to N losses from treatments in which a high proportion of the N fertilizer was applied early in the growing season, contributing to higher yields where N applications had been applied later in the growing season. Although results of this study have not demonstrated a consistent yield benefit from split application of N, split-applying N fertilizer at planting and hilling may help to reduce the potential for N losses early in the growing season. Split-applying N may reduce the amount of N present in the soil as NO3, a form of N that may be susceptible to loss through leaching and denitrification. In 2005, the timing of N application also influenced total tuber yield but, unlike 2004, the 4x split treatments produced a total yield that was similar to the preplant treatment but greater than the 2x split. In 2006, treatments receiving N fertilizer had a higher total yield than a check treatment receiving no N fertilizer in any form. However, for treatments to which N was applied, neither rate nor timing of N application influenced total tuber yield. Differences among years in the effects of timing of N application on total yield appear to be due, at least in part, to growing season conditions. In 2003 to 2006, which had generally good growing conditions and low-to-average rainfall, timing of N application had no effect on total yield. However, the difference in the effect of
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