NITROGEN-FERTILIZATION OF WHITE RIESLING GRAPES IN WASHINGTON - NITROGEN SEASONAL EFFECTS ON BUD COLD-HARDINESS AND CARBOHYDRATE RESERVES

A commercial vineyard of White Riesling was used to study the influenc e of 0, 56, 112, and 224 kg N/ha on bud cold hardiness and carbohydrat e reserves of bud and cane tissues over a three-year period. High N ha d significant effects on cold hardiness of buds, levels of soluble sug ars and starches extracted from one-year-old bud or cane samples, only on a limited number of dates during the three years of the study. The re was a positive relationship between bud hardiness and soluble sugar s from bud or cane samples that was highly significant. Regression ana lysis of yearly data indicated there was no relationship between nitro gen level and either soluble sugars or starch in buds or canes; There was a positive relationship between air temperature and bud low temper ature exotherms during the sampling period of each year, and an invers e relationship between air temperature and soluble sugar levels in bot h buds and canes. These data show the predominant role of air temperat ure on bud and presumably vine cold hardiness and the attendant change s in carbohydrate reserves. This study further demonstrates that under otherwise good management practices of pruning, cropload, irrigation, and rootstock selection, there should be little concern regarding a d etrimental influence of nitrogen applied before harvest on cold hardin ess or carbohydrate reserves of grapevines.