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Julie M. Tarara

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Paul E. Blom and Julie M. Tarara

Most yield estimation practices for commercial vineyards are based on longstanding but individually variable industry protocols that rely on hand-sampling fruit on one or a small number of dates during the growing season. Limitations associated with the static nature of yield estimation may be overcome by deployment of trellis tension monitors (TTMs), systems that provide dynamic measurement of changes in the tension of the main trellis support wire. In 10 commercial vineyards from which two commercial juice processors annually collect data to derive yield estimates, TTMs were installed. Processor and TTM data were subjected to three permutations of the basic linear computational approach to estimating yield and their accuracies evaluated given known harvested yield at various spatial scales. On average, TTM data produced more accurate estimates of actual yield than did the computational protocols of the juice processors. There was high vineyard-to-vineyard variability in the accuracy of the estimate under all approaches, even from those permutations designed to match the spatial scale of the data collected for yield estimation with the spatial scale of the actual harvested yield. The processor protocols appear to be more sensitive than the TTM approach to the selection of the antecedent years used for comparison with the current year's data. Trellis tension monitoring may be useful to supplant traditional, labor-intensive yield estimation practices or to supplement longstanding practices with real-time information that can be applied to dynamic revision of static yield estimates.

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Julie M. Tarara and Gwen-Alyn Hoheisel

The importance of shielding temperature sensors from solar radiation is understood, but there is a lack of prescriptive advice for plant scientists to build inexpensive and effective shields for replicated field experiments. Using the general physical principles that govern radiation shielding, a number of low-cost, passively ventilated radiation shields built in-house was assessed for the measurement of air temperature against the same type of sensor in a meteorological “standard” Gill radiation shield. The base shield material had high albedo (≈0.9) and low emissivity (0.03). Aspirated shields were included for simultaneous measurements of temperature and relative humidity. Differences in air temperature (ΔT) between low-cost shields and the standard Gill were greatest for shields with open bottoms (up to +7.4 °C) and for those with poorly perforated sidewalls. Open-bottomed shields were prone to heating from reflected radiation. Tube-shaped shields appeared to require more than 30% sidewall perforation for convection by ambient wind (up to 4 m·s−1) to offset the midday radiation load of the shield. The smallest daytime ΔT were between aspirated shields and the standard Gill, averaging less than ±0.5 °C. Among passively ventilated shields, the smallest daytime ΔT consistently were produced by a shield that emulated the stacked plate design of the standard Gill for a total of U.S. $4.00 in materials and 45 min construction time. Eighty-nine percent of all daytime ΔT for the “homemade Gill” shield was 1.5 °C or less. The combination of low ambient wind speed (less than 1 m·s−1) and high global irradiance (greater than 600 W·m−2) produced the largest ΔT for all passively ventilated shields, the magnitude of which varied with shield design; stacked plate configurations were more effective shields than were tube-based configurations. Nighttime ΔT were inconsequential for all shields. Cost-effective radiation shielding can be achieved by selecting shield materials and a configuration that minimize daytime radiation loading on the shield while maximizing the potential for convective transfer of that radiation load away from the shield and the sensor it houses.

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Julie M. Tarara and Jorge E. Perez Peña

To determine the effects of timing and extent of regulated deficit irrigation (RDI) on grapevine (Vitis vinifera) canopies, whole-canopy transpiration (TrV) and canopy conductance to water vapor (g c) were calculated from whole-vine gas exchange near key stages of fruit development. The vines were managed under three approaches to RDI: 1) standard industry practice (RDIS), or weekly replacement of 60% to 70% of estimated evapotranspiration (ET) for well-watered grapevines; 2) early additional deficit (RDIE), or one-half of RDIS applied between fruit set and veraison; and 3) late additional deficit (RDIL), or one-half of RDIS applied between veraison and harvest. Compared with RDIS, the additional deficits (RDIE, RDIL) reduced daily cumulative Trv by about 45% (RDIE) and about 48% [RDIL (57% by unit leaf area)]. Diurnal patterns of g c indicated consistent moderate water stress in all RDI regimens (g c ≈50–150 mmol·m−2·s−1). Under RDIE and RDIL, there were transient occurrences of severe water stress, indicated by g c declining below 50 mmol·m−2·s−1. Across the day, vines under RDIE and RDIL had lower g c than RDIS. Under all deficit regimens, TrV exhibited opposing hysteretic loops with solar radiation [photosynthetic photon flux (PPF)] and vapor pressure deficit (VPD), with less sensitivity to VPD in RDIE and RDIL. For a given value of VPD, TrV was higher in the morning than in the afternoon. For a given value of PPF, TrV was higher in the afternoon than in the morning. Single-leaf measurements of transpiration overestimated TrV by an average of 45%. Instantaneous water use efficiency (WUE) declined during midday at the pre- and postveraison measurements for all RDI regimens. Whole-canopy daily integrated WUE (WUEd) did not differ among regimens during the additional deficits because daily cumulative values of whole-vine net carbon exchange (NCEV) and TrV changed proportionally: by about 43% to 46% in RDIE relative to RDIS. The case was less clear-cut for RDIL, where NCEv declined by 33% and TrV by 48% relative to RDIS. However, WUEd did not differ significantly between the two. More substantial water deficits than those are currently practiced in the industry through RDI could be used for potential water savings in semiarid climates.

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Julie M. Tarara, Bernardo Chaves and Bernadine C. Strik

Grow tubes are well established in forestry and are gaining attention in establishing some woody perennial crops. To date, microclimate descriptions have addressed the aboveground environment, but a mulched raised bed system with organic mulch-incorporated soil requires both the above- and belowground microclimate to be quantified. We measured the microclimate of commercially used, non-ventilated translucent and non-ventilated opaque grow tubes in a model crop of blueberry (Vaccinium corymbosum L.) grown on sawdust-mulch-covered raised beds formed from sawdust-incorporated tilled soil. The differences in air temperature between tubes and ambient were consistent with those reported in the literature. Air temperature in translucent tubes was up to 19.7 °C higher than ambient. Differences in vapor pressure deficit were largely a function of differences in air temperature between tubes and ambient rather than actual vapor pressure. Stem temperatures were highest outside of the tubes as a result of radiation load. The surface temperature of ambient sawdust mulch (maximum 53 °C) was up to 14 °C above that in the translucent tube and 20 °C above that in the opaque tube. The largest gradients in the bed system were between the loose dry mulch and the soil–mulch interface. The presence of a grow tube did not influence soil temperature or its daily amplitude at 15 cm below the surface—the native tilled soil. Temperatures associated with the opaque tubes were between ambient and those in the translucent tubes. The temperature data indicate that both opaque and translucent unventilated grow tubes should influence shoot and crown growth but may have little influence on root growth in this shallow-rooted plant.

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Bernadine C. Strik, Gil Buller and Julie M. Tarara

Grow tubes are sometimes used in blueberry (Vaccinium corymbosum L.) to establish plantings or replace dead plants in older fields. Two experiments were conducted at a commercial farm to evaluate the effect of various grow tubes used during planting establishment of highbush blueberry cultivars. The treatments in the first experiment were cultivar (‘Aurora’, ‘Elliott’, ‘Liberty’) and grow tube treatment (no tube, control; opaque cardboard tube in the first growing season; and opaque plastic tube in the first season or first through the second season). The treatments in the second experiment were cultivar (‘Aurora’, ‘Elliott’, ‘Liberty’, ‘Ozarkblue’) and grow tube treatment (control; translucent plastic; opaque plastic; and wire mesh tube over plants in the first growing season). The presence of a grow tube from spring to fall of the first growing season decreased crown dry weight (DW) by an average of 37% to 50% and root DW by 30% (all except translucent plastic in Expt. 2) and increased the aboveground:belowground DW ratio relative to the control by an average of 34% to 67%, depending on the experiment. Plants grown in tubes were taller, had a narrower canopy, and had fewer whips, likely a response to low light levels inside the tubes; the fewest whips were found in the opaque plastic or cardboard tubes and the most in the translucent plastic tube with an intermediate response in the wire mesh tube. Removal of grow tubes during the summer led to plant damage from sudden sun exposure. The opaque grow tubes (present in Year 1) reduced yield/plant in Year 2 for ‘Elliott’ and ‘Liberty’ (cardboard tube only) but not ‘Aurora’. Pruning plants to allow for limited early fruit production (≈0.6 kg/plant) in Year 2 did not reduce yield in Year 3 (≈2.7 kg/plant). Whereas grow tubes reduced root and crown growth in the first season, there appeared to be no longer-term adverse effect on aboveground plant growth or yield.

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Julie M. Tarara, Bernardo Chaves and Bernadine C. Strik

Microclimate variables were integrated over a 6-month period during which blueberry (Vaccinium corymbosum cv. Liberty) bushes were grown in 51-cm high, 20-cm diameter round grow tubes (opaque or translucent) on a sawdust mulch-covered raised bed with the mulch incorporated into tilled soil. Grow tubes were installed around plants in the spring of 2006, 5 months after planting. Total photosynthetic photon flux (PPF) density was 55% and 21% of ambient in translucent and opaque tubes, respectively. Daily maximum vapor pressure deficit consistently was highest in translucent tubes. Air (Ta) and stem (Tstem) temperatures in both grow tube types exceeded Ta and Tstem in non-tubed plants (ambient). Maximum mulch surface temperature (Tm) was lowest in opaque tubes, whereas there was no difference in Tm between ambient and translucent tubes. The soil–mulch interface temperature (Tsm) was warmer outside tubes than Tsm inside tubes. Soil temperatures directly under the tubes differed very little between tube types and ambient, generally less than 1 °C. Root and crown dry mass (DM) did not differ between tubed plants and ambient at the end of the establishment year. Leaf area, leaf DM, and fruit bud number were suppressed inside tubes. All plants were greater than 51 cm tall at the end of the growing season. Substantial compensatory growth occurred above tubes: tubed plants were more upright and had more leaf area, leaf DM, and shoot growth than ambient plants above 51 cm. However, there was no difference between tubed and ambient plants in fruit bud number, total plant leaf area, shoot:root, or DM of 1- and 2-year-old wood. Grow tubes can alter microclimate and architecture of young blueberry bushes but have no significant influence on size and distribution of total DM after one growing season in the field.

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Julie M. Tarara, Bernardo Chaves, Luis A. Sanchez and Nick K. Dokoozlian

The lag phase (L) of grape berry growth is used to determine the timing of hand sampling for yield estimation. In commercial practice, growers apply scalars to measurements of berry of cluster masses under the assumption that fruit was assessed during L, which is the short period of slowest increase in fruit mass that occurs between the first and second sigmoid curves that describe growth in fleshy fruits. To estimate L, we used an automated remote system that indirectly detects increases in vegetative and fruit mass in grapevines by monitoring the tension (T) in the main load-bearing wire of the trellis. We fitted logistic curves to the change in TT) such that the parameters could be interpreted biologically, particularly the onset of L: the asymptotic deceleration of growth. Curves fit the data well [root mean square error (RMSE) 4.2 to 14.9] in three disparate years and two vineyards. The onset of L was most sensitive to the inflection point of the first logistic curve but relatively insensitive to its shape parameter. The analytical solution of the second derivative of the first logistic curve for its minimum predicted the apparent onset of L with a range of 3 to 5 days among replicates. The roots of the third derivative allowed analytical solutions for the onset of the first rapid growth phase and L, consistently predicting the onset of L 2 to 15 days earlier than was identified by trained observers who examined ΔT curves. Remote sensing of ΔT could better time field sampling and decrease current reliance on visual and tactile assessment to identify the onset of L, thus improving yield estimation in grapes.

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Julie M. Tarara, Paul E. Blom, Bahman Shafii, William J. Price and Mercy A. Olmstead

Estimates of canopy and fruit fresh mass are useful for more accurate interpretation of data from the Trellis Tension Monitor, a tool for real-time monitoring of plant growth and predicting yield in trellised crops. In grapevines (Vitis labruscana Bailey), measurements of shoot and fruit fresh mass were collected at frequent intervals (14 to 21 days) over 5 years, and these data were correlated with variables that could be obtained nondestructively: shoot length, number of leaves per shoot, and number of clusters per shoot. Shoot length provided a good estimator of shoot fresh mass in all years. Nonlinear logistic regression models described the dynamics of canopy growth from bloom to the early stages of ripening, which often is poorly represented by simple linear regression approaches to seasonal data. A generalized function indicated a lower bound of ≈600 degree-days, after which an increase in shoot fresh mass could be considered on average to contribute only slightly to further increases in trellis wire tension. The dynamics of fruit mass were captured adequately by a nonlinear function, but not as well as vegetative mass because of larger variances in fruit mass. The number of clusters per shoot was associated with fruit mass only after the accumulation of ≈550 degree-days or, equivalently, the time at which fruit mass exceeded ≈25 g per shoot. Seasonal dynamics of the ratio of fruit to vegetative fresh mass were not sufficiently discernable by the logistic models because of the dominance of fruit mass and its large interannual variation.

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Alison L. Reeve, Patricia A. Skinkis, Amanda J. Vance, Jungmin Lee and Julie M. Tarara

Vigor and crop level management are important practices for premium wine grape production. The implications of crop thinning ‘Pinot noir’(Vitis vinifera L.) vines of varying vigor were investigated in the Willamette Valley of Oregon in 2011 to 2013 to better understand the relationship between canopy size and yield within the framework of a cool-climate, premium production wine grape vineyard. To manipulate vigor, a competitive grass cover crop (Festuca rubra L.) was grown in both (Grass), alternating (Alternate), or neither side of the flanking alleyways (Tilled). Vines within each vineyard floor treatment had two crop levels applied, including cluster thinning to one cluster per shoot (Half Crop) or no crop thinning (Full Crop). Grass treatment had reduced leaf area and leaf nitrogen (N) concentrations during all years compared with Tilled treatments. Leaf photosynthesis was also lower in Grass treatments despite more light in the canopy interior. Grass treatments had lower yield than Tilled treatments in 2 of 3 years and lower yeast assimilable nitrogen (YAN) concentrations in fruit every year. There was limited impact of floor treatments on total soluble solids (TSS) and pH. Reduced yields through cluster thinning had limited impact on vegetative growth but increased TSS and pH, in 2 of 3 years. There were few floor management by crop level interactions in any year. Grass effectively reduced vegetative growth to moderate vigor levels with cane weights between 20 and 40 g. Using a competitive grass cover crop may be an effective strategy to reduce excessive vine growth and require less labor in canopy management and crop thinning without compromising basic fruit ripeness, although YAN levels need to be monitored.