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Grapevines grown in low-phosphorus (P) soils typical of western Oregon vineyards may benefit from additional P applied to the canopy using foliar sprays. Alternatively, vines may be negatively affected by foliar P sprays because lower root colonization by arbuscular mycorrhizal fungi (AMF) could reduce uptake of other nutrients or increase vine water stress. The impact of foliar P sprays on vine growth, vine nutrient and water status, AMF colonization, and fruit yield and quality was studied in two ‘Pinot noir’ vineyards with a history of low vine P status over 3 years. Three foliar spray treatments [phosphite, phosphate, water (control)] were applied to vines three times each season using a standard air-blast sprayer at a commercial vineyard. Two foliar spray treatments (phosphite, water) were applied using a hand sprayer at a smaller research vineyard. Phosphite sprays increased leaf blade and petiole P concentrations and reduced arbuscular colonization of roots at the research vineyard, but neither phosphate nor phosphite significantly affected these variables at the commercial vineyard. Foliar P sprays had no effect on vine growth, vine water relations (leaf water potential and stomatal conductance), yield, or fruit quality attributes at either site. These results indicate that there is little benefit to spraying the canopy of grapevines with P, even in vineyards with low P status.

Grape growers rely on tissue tests of leaf blades or petioles for routine monitoring of vine nutritional health and for diagnosing potential nutrient deficiency or toxicity. There has been a long-standing debate as to which tissue better reflects the nutrient status of vines. A comparison of leaf blade and petiole nutrient concentrations was carried out to investigate which tissue better relates to vine growth, yield, and must nutrient responses of ‘Pinot noir’ grapevines to varying levels of nitrogen (N), phosphorus (P), and potassium (K) supply using data from a pot-in-pot vineyard over 4 years. Leaf blades and petioles were collected at 50% bloom and 50% veraison in each year and N, P, and K concentrations were assessed as predictors of leaf area at veraison, pruning mass at dormancy, yield, and must nutrient concentrations at fruit maturity. Data from commercial ‘Pinot noir’ vineyards were also used to investigate the relationship between leaf blade and petiole N concentrations with must N levels. Results indicated that leaf blades were superior to petioles in predicting vine growth, yield, and must yeast assimilable nitrogen (YAN) responses across a wide range of vine N status at both sampling times. Leaf blade N was a better predictor than petiole N in predicting YAN using data sets from both the pot-in-pot vineyard and commercial vineyards. Relationships between leaf blade and petiole concentrations of P and K and vine response variables generally did not differ and both tissues appeared to be equally effective in predicting P and K effects on growth, yield, and must P or K levels. Although petiole P was slightly better than leaf blade P at bloom in predicting must P levels, and models including both leaf and petiole K simultaneously as predictors relied only on leaf K. For all three nutrients, sampling at bloom and veraison had a similar predictive strength for response variables. Based on these findings, we recommend using leaf blades as opposed to petioles for diagnosing the N, P, and K status of ‘Pinot noir’.

‘Pinot noir’ grapevines were grown in a pot-in-pot system using a red-hill-soil where volumetric soil water content (θ_v) was carefully controlled. Four-year-old vines were supplied with one of two irrigation regimes (wet or dry) between véraison and fruit maturity and the experiment was repeated over 2 years. From véraison to harvest, vines in the wet treatment received irrigation whenever θ_v approached ≈15% maintaining leaf water potential (Ψ_leaf) above –1.0 MPa. Vines in the dry treatment received irrigation when θ_v approached 11% to 12% and experienced significant water stress (Ψ_leaf ≈–1.4 MPa) before water was re-supplied. Vines were destructively harvested at véraison and at fruit maturity to determine biomass and nutrient content in the current season’s above-ground tissues. Fruit yield, maturity indices, and must nutrient composition were measured at maturity. Irrigation did not influence vine growth in either year nor did it influence yield or fruit maturity indices. Irrigation also had no influence on leaf, whole cluster, or must mineral nutrient concentrations. Vine growth, yield, and nutrient status in leaves and musts varied by year. Vegetative growth was greater in 2007 than 2008, whereas yield and cluster weights were greater in 2008. Also in 2008, whole clusters obtained a greater proportion of dry matter and nutrients after véraison when differing irrigation treatments were imposed. Nonetheless, irrigation did not affect must chemical composition. These findings suggest that periodic post-véraison water deficits that are moderate to severe have little effect on berry nutrient and sugar accumulation in ‘Pinot noir’ cropped at typical levels for this variety.

Grapevines rely on arbuscular mycorrhizal fungi (AMF) to obtain ample phosphorus (P) from soils with low to moderate P like the Ultisols of western Oregon. Prior research indicated that nine species, or virtual taxa, of AMF colonized the roots of ‘Pinot noir’ at greater than 1% abundance in a single vineyard. However, little is known about how different taxa within a community vary in their capacity to function as symbionts with grapevines. The effectiveness of five native AMF species representing five genera to promote growth and nutrient uptake of ‘Pinot noir’ was examined in a fumigated Ultisol soil under well-watered and periodically dry conditions. Plants were grown with each of the different isolates alone or without AMF. After 8 and 16 weeks, whole vines were destructively harvested and biomass and nutrients were determined. Results showed that four of the isolates colonized roots extensively, increased root and shoot biomass, and predominantly increased P uptake. A Claroideoglomus isolate was superior in promoting shoot growth as compared with Rhizophagus irregularis, even though both isolates increased P uptake to the same extent, suggesting a higher carbon cost for R. irregularis. Scutellospora calospora failed to colonize roots beyond a trace and had no impact on vine performance. The ability to increase P uptake among the four effective fungi was not related to the frequency of arbuscules in roots suggesting that some P exchange occurs via hyphae within the cortex, particularly for Funneliformis mosseae. Water limitation reduced P uptake as a main effect across all mycorrhizal treatments, suggesting that the native isolates studied here have similar functionality under well-watered and periodically dry conditions.

The nutrient uptake and distribution patterns for N, P, K, Ca, and Mg were determined in mature (23 to 24 year old), field-grown, rainfed grapevines (Vitis vinifera L. `Pinot noir') growing in a red hill soil in Oregon in 2001 and 2002. Biomass, nutrient concentrations, and nutrient contents of all plant organs, including roots, were determined on 14 sampling dates over 2 years. There was no seasonal change in the standing biomass of primary roots (fine feeder roots), small woody (<4 mm diameter) or large woody (>4 mm diameter) roots. Trunk biomass also did not change during the 2 years, but all other vine organs showed significant seasonal changes in biomass. The rate of N uptake was greatest at bloom, when remobilization from reserves was also high. Nitrogen was also taken up after leaf fall in 2001, but not in 2002, when an early frost occurred before soil moisture recovery by fall rains. Uptake of N, K, and Ca from soil was similar between years, even though canopy demand for N and K was greater in 2002 (significantly larger crop). Phosphorus uptake from soil was lower in 2002 than in 2001, which was most likely due to the drier conditions in 2002. A greater quantity of canopy N, K, and especially P was supplied from stored reserves in the drier 2002 growing season. About 50% of canopy requirements for N and P were remobilized from reserves in the trunk and roots by the time of fruit maturity in 2002. Only 15% of canopy K and <5% of canopy Ca or Mg came from stored reserves in 2002. Our findings indicate that nonirrigated grapevines grown in Oregon acquire nutrients from soil earlier in the growing season and have a greater reliance on stored reserves of N and P than reported in previous studies from other growing regions. Replenishment of nutrient reserves occurred to large extent during the postharvest period. Rainfed vineyards in Oregon may require different nutrient management practices than irrigated vineyards, since low soil moisture may limit summer uptake of P.