Nitrogen Fertilization of White Riesling Grapes in Washington: Nitrogen Seasonal Effects on Bud Cold Hardiness and Carbohydrate Reserves R. L. WAMPLE ~*, S. E. SPAYD 2, R. G. EVANS 3, and R. G. STEVENS 4 A commercial vineyard of White Riesling was used to study the influence of 0, 56, 112, and 224 kg N/ha on bud cold hardiness and carbohydrate reserves of bud and cane tissues over a three-year period. High N had significant effects on cold hardiness of buds, levels of soluble sugars 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. There was a positive relationship between bud hardiness and soluble sugars from bud or cane samples that was highly significant. Regression analysis of yearly data indicated there was no relationship between nitrogen level and either soluble sugars or starch in buds or canes. There was a positive relationship between air temperature and bud low temperature exotherms during the sampling period of each year, and an inverse relationship between air temperature and soluble sugar levels in both buds and canes. These data show the predominant role of air temperature on bud and presumably vine cold hardiness and the attendant changes 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 detrimental influence of nitrogen applied before harvest on cold hardiness or carbohydrate reserves of grapevines. KEY WORDS: bud cold hardiness, carbohydrates, nitrogen fertilization, White Riesling vines Nitrogen (N) is the predominant nutrient applied on an annual basis throughout most of the grape growing regions of the world. The scheduling of N applications and determination of appropriate levels have been the subject of numerous research projects (1,4,5,6,7 ,9,14,15,16,18,38,39). Additional studies have attempted to establish the uptake, metabolism and storage of nitrogenous compounds and how fruit yield and quality are affected (2,14,15,19,22,24). However, numerous questions regarding the influence of nitrogen on cold hardiness and carbohydrate reserves have been raised as a consequence of these studies and their recommen- dations (3,9,12,13,16,25,32). Low temperature injury, the stimulus for many of these questions, has not been restricted to northern temperate growing regions (36). Understanding grapevine cold hardiness is further com- plicated by our limited understanding of trunk, cordon, and cane hardiness as compared to bud hardiness. The interpretation of nitrogen-related cold hardiness stud- ies in grapes is complicated by the use of rootstocks which have specific nutrient uptake characteristics and 1Associate Horticulturist, 2Associate Food Scientist, 3Associate Agricultural Engineer, and "Associate Soil Scientist respectively, Washington State University, Irrigated Agriculture Re- search and Extension Center, Prosser, WA 99350-9687. *Author to whom correspondence should be addressed. H/LA Paper No. 91-29. Project No. 3519. College of Agriculture and Home Economics Research Center, Washington State University, Pullman, WA 99164 The authors acknowledge support from the Washington Wine Grape Advisory Board, Stimson Lane Wine and Spirits and Washington State University. The assistance of Andy Bary, Alan Kawakami, Barbara Seymour, and Anna Wichers of Washington State University and J. Andersen, G. Ballard, K. Corliss, J. Johnson, A. Litton, and R. Wheeler of Stimson Lane Wine and Spirits is greatly appreciated. Manuscript submitted for publication 25 October 1991. Copyright © 1993 by the American Society for Enology and Viticulture. All rights reserved. 159 physiological influences on the scion (7,11,20,21,27,29,33,38). The generally accepted rela- tionship, as stated by Pellet and Carter (25), is that high nitrogen fertilizer rates reduce grapevine cold hardi- ness, yet these same authors note that few studies have specifically examined this question, and most of the literature is not conclusive. This is in part due to the variability in genetic, environmental and cultural fac- tors. The purpose of this research was to examine the effect of nitrogen in conjunction with other standard cultural practices on the bud cold hardiness and bud and cane carbohydrate reserves of White Riesling grape- vines in south central Washington. Materials and Methods Vineyard: The study was conducted from 1985 - 1989 at the Chateau Ste. Michelle's (CSM) Cold Creek vineyard, 25 km north of Sunnyside, Washington. The plot consisted of about 12 ha of own-rooted Vitis vinifera L. cv. White Riesling. The soil is a Warden silt loam which has an underlying Caliche layer. Field capacity of the soil was about 28 cm/m (27% to 28% moisture by volume). Permanent wilting point was about 8 to 10 cm/ m (8% to 10% by volume). The land had not been cultivated prior to vineyard establishment in 1978. Based on soil sampling, the land was ripped to a depth of 1 m to breakup a caliche layer and fertilized as recommended by Dow et al. (8). The vines were planted in 1978 on a 1.8 × 3.0m spacing and trained to a bilateral cordon system with two catch wires. Maximum and minimum temperatures, precipitation, and relative Am. J. Enol. Vitic., Vol. 44, No. 2, 1993