| Abstract |
- This study integrates various vineyard practices that may improve nitrogen
availability to the vine, particularly during ripening. Different strategies aimed at
increasing yeast assimilable nitrogen in the fruit at harvest have been evaluated.
This study seeks to improve fermentation behavior and wine quality through
vineyard practices used for nitrogen management. The focus of this study is to
optimize fruit quality and maximize the juice nitrogen fraction, while maintaining a
physiologically healthy vine and crop system.
Treatments were applied in a factorial design to vary irrigation, cultivation,
and nitrogen application to Pinot noir and Chardonnay grapevines in two
commercial Oregon vineyards during the 1999 and 2000 growing seasons. Irrigated
vines received supplemental irrigation after lag phase. Cultivation of alternate rows
was performed in early spring to encourage nitrogen utilization and reduce nutrient
and water competition. Nitrogen treatments consisted of soil-applied urea
(39.2kgN/ha), foliar applied urea (2.98kgN/ha), and zero nitrogen. Soil nitrogen was applied in early spring. Foliar nitrogen was applied once at the onset of
ripening and again at veraison. The trials were established at Knudsen Vineyard
located in the North Willamette Valley and Benton Lane Vineyard in the South
Willamette Valley in 1999.
At Benton Lane Vineyard, photosynthesis, transpiration, water use
efficiency, chlorophyll content, maximum quantum yield of photosynthesis, soil
moisture, leaf petiole nutrition, pruning weights, and carbohydrate reserves were
measured during the 1999 and 2000 growing seasons. Leaf water potentials were
measured during the 2000 growing season. During both seasons irrigated vines
assimilated CO₂ and transpired at a significantly higher rate than non-irrigated
vines. Similarly, tilled treatments assimilated CO₂ at a significantly higher rate and
maintained higher water use efficiency. Tilling tended to increase the efficiency of
light driven photosynthetic reactions and chlorophyll content. This response
became more apparent in the second year of the study, which may indicate a
delayed effect of soil cultivation on maximum quantum yield of photosynthesis and
chlorophyll content in grapevines. Nitrogen treatments had little impact on leaf gas
exchange and chlorophyll content. Soil Cultivation had the largest impact on
petiole nutrient content, with significant differences in phosphorus, potassium,
manganese, copper, boron, carbon and total nitrogen. Irrigation increased total
petiole nitrogen in the second year of the study. Pruning weights increased with
cultivation in both years and cane weights were higher after the second year.
Irrigation and nitrogen did not affect vine vigor. Ripening dynamics, juice composition, and yield components were
measured at both vineyards during the 1999 and 2000 growing seasons. During
both seasons, irrigated Pinot noir vines had lower titratable acidity than non-irrigated
vines and tilled treatments had higher soluble solids than non-tilled
treatments. Tilled Chardonnay vines had lower soluble solids and higher titratable
acidity in 2000. In 1999, from the onset of ripening until harvest, the ammonia
content of Pinot noir fruit decreased from an average of 80 to 30 (mg/L) while the
alpha amino acid content increased from 60 to 150 (mg/L) during ripening. The
YANC of Pinot noir vines increased from 100 to 190 (mg/L), predominately due to
a large increase in alpha amino acid concentration in the last two weeks of
maturation. For both Pinot noir and Chardonnay, the results from 2000 indicate that
tilled treatments tend to have higher YANC at harvest, predominately due to a large
increase in alpha amino acids. Significant effects from tilling suggest that there
may be a delayed benefit from soil cultivation. Irrigated vines tended to have a
higher berry weight, however, yield components differed only slightly between
treatments and year.
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