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Management strategies like “deficit irrigation” in wine grapes require accurate, reliable information on vine water use, making direct measurements of vine transpiration highly desirable. The heat-balance sap flow method has the advantages of being non-invasive and requiring no other calibration beyond a zero-flow set. Potential violations of the method's assumptions were dealt with and the heat balance method successfully applied to mature grape vines under conditions of extremely high sap flow. Greenhouse studies suggested that vines transpire at night, up to 9.5% of the total 24-h water loss, thus violating the zero-flow assumption for setting the gauge constant. Using a predetermined gauge constant caused smaller errors than using daily, pre-dawn constants set in situ. The steady-state assumption was violated only in early and late hours of the day, and the inclusion of a term to account for the change in heat stored by the stem only marginally improved daily estimates of water use. The assumption of radially uniform temperature across the heated stem segment is violated at very high flows (e.g., >700 g·h–1), but can be corrected for by using wider heaters and adjusting the placement of thermocouples. For a mature, potted vine in the greenhouse, the maximum absolute error in cumulative daytime water use between a sap gauge and a precision load cell was about –10%, with the gauge almost exclusively underestimating water loss. A custom-built, 20-gauge system was run continuously in the field for 90 days. Vine-to-vine variability in water use was not accounted for by normalizing sap flow by leaf area, suggesting that it is critical to include in any field study the largest number of gauges that are technically feasible.

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Abstract

Wine grape (Vitis vinifera L.) vineyards in much of the desert Southwest are frequently exposed to intense solar radiation, high vapor pressure deficits, and high air temperatures. Although wine grape production in this region has increased during recent years, the harsh environment often results in growth conditions that may be suboptimal for photosynthesis and other plant processes, ultimately affecting fruit yield, wine color, and acidity.

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growers do not apply the principles of canopy management because of cost and time constraints ( Terry and Kurtural, 2011 ). To remain profitable, growers tend to retain too many nodes during dormant pruning, resulting in out-of-balance vines with less than

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., 2000 ). An important sector of the Canadian economy is the production of field vegetables for fresh and processing markets, which in 2007 accounted for nearly $267 million in farm value in the province of Ontario alone ( Mailvaganam, 2008 ). Vine crops

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trees ( Psarras et al. 2000 ) and cranberry vines ( Atucha et al. 2021 ), which may result in increased N uptake and, consequently, plant reserves. An increase in plant reserves in fall may contribute to enhanced plant growth the following spring

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The extent of translocation of 14C-labeled photosynthates from the senescent leaf to the parent vine before leaf abscission and the short-term effects of premature leaf removal on the carbohydrate balance of the vine were studied by using autoradiography and trapping 14CO2 respired from the treated leaf. The treated leaf abscissed 1.5 days after administering the label. The plant was harvested after natural leaf abscission. The radioactivity recovered from the plant, excluding the treated leaf, was 20% of the input. Radioactivity was detected in the roots, trunk, shoot, and leaves. Most of the radioactivity remained in the trunk and the young and old roots. The implications of premature leaf removal by mechanical harvesting on the carbohydrate balance of the vine are discussed.

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An increase in mechanical pruning of Concord grapevines in Washington has led to a marked increase in yield. In 1993 the average yield for the 20,000 plus acres was slightly greater than 12 ton/acre. As part of a long term study, initiated in 1987, to evaluate the effects of mechanical pruning on Concord yield and fruit quality, we have also followed bud cold hardiness and winter injury over several years. Cold hardiness was monitored using low temperature exotherm analysis of excised buds. Winter injury was evaluated by visual examination of bud and cane tissues collected from vines with different croploads. In 1990 the average yield for mechanically pruned vines was 13T/ac and for balance pruned vines about 8T/ac. Winter injury during December 1990 showed significantly less injury to mechanically pruned vines whether primary, secondary or tertiary buds were examined. During the winter of 1991-92 and 1993-94 bud cold hardiness of individual vines showed no relationship to cropload per vine.

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An ongoing study measuring grapevine (Vitis vinifera L., cv. Thompson Seedless) water use with a weighing lysimeter is being used to develop a model to simulate vine water use on both a diurnal and seasonal basis. A method to calculate the aerodynamic resistance (ra) of the vines was first determined. Subsequently, a model to predict canopy resistance (rc based solely upon intercepted photon flux density (PFD) was developed. The modeled values of ra and rcwere substituted into a resistance-energy balance equation to predict vine ET. The modeled parameters were validated against diurnal measurements of ET from the lysimeter. The greatest difference between modeled and measured rc occurred prior to 1000 h and subsequent to 1500 h each day. The model overestimated vine ET by 14 and 23% on 16 and 24 June, 1992, respectively. Ambient temperature and vapor pressure deficit were greater on 24 June than on 16 June. Refinements in calculating PFD interception by the vine's canopy early and late in the day and incorporating the effects of other environmental factors on grape stomatal conductance should improve the predictive capabilities of the model.

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Winter buds of `Concord' and `Niagara' grapevines were dissected and their embryonic clusters scored to developmental stage. Stage was regressed against flower and fruit number per cluster the following year to see if flowering or fruiting potential could be gauged from bud morphology. `Concord' vines were either minimal-pruned (MP) or balance-pruned (BP) and non-irrigated or provided supplemental irrigation. `Niagara' vines were BP vines which were non-irrigated, irrigated, or nitrogen fertigated. Winter buds of MP `Concord' were significantly less developed than buds of BP vines, and flower and fruit number per cluster also significantly less. Irrigation did not affect bud construction or flower or fruit number per cluster in either pruning regime. Winter buds of `Niagara' had similar cluster stages in all treatments and there were similar flower and fruit number per cluster the following season. Within cultivar and year, there was a positive linear relationship between mean flower number or fruit number per cluster and mean stage of cluster differentiation within buds the previous dormant period. In `Concord', a given winter cluster stage allowed production of significantly more flowers and fruit in 1992 than it did in 1993. A bud's flowering potential thus varies from year to year and depends on factors not solely related to bud morphology.

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Proper variety selection and production practices are critical to obtaining profitable yields of mechanically harvested pickling cucumbers (Cucumis sativus L.). On the Delmarva peninsula, the tractor-mounted harvester, which utilizes the pinch-roller system for separating the pickles from the vine, was used exclusively for harvest until 1998. The pull-type forced-balance shaker machines have been introduced as an alternative harvest system. Replicated commercial-size variety trials have been conducted for four consecutive years. The trials are planted twice during the growing season, reflecting the climactic differences associated with early-season and late-season plantings. `Vlaspic' and `Lafayette' are standard varieties. Promising new varieties include `EX 1914' and `SQRP 1882'. Investigations to determine optimum plant populations and row spacing have determined that three-row beds with 60,000 plants per acre provide the highest yields and best quality fruit. Optimal operating speeds and picking reel speeds of 1.4 mph and 45 rpm, respectively, have been determined for the tractor-mounted machine. Additional design improvements have been implemented and evaluated to reduce damage. Fifty-nine replicated commercial tests evaluating the tractor-mounted harvester and the forced-balance shaker type indicate much greater harvest and throughput efficiencies are associated with the forced-balance shaker harvester, resulting in improvements between $65 and $100 per acre.

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