). Table 1. Description of study sites used to collect data for calibration and validation of growing degree-day models developed for lowbush blueberry in Nova Scotia, Canada. z Weather data. Hourly air temperature at each site was monitored using
Abstract
Second-order rectangular hyperbolic and asymptotic models which predict spur and terminal leaf expansion of ‘Montmorency’ sour cherry (Prunus cerasus L.) were developed from leaf area observations and temperature records made in orchards near East Lansing, Mich. Average leaf area per leaf was more highly correlated with degree-day accumulation at a base of 4°C starting April 19, than with day of the year. Leaf area per leaf increased linearly with degree-day accumulation until full leaf expansion. Final spur or terminal leaf size was not constant between years.
Abstract
A model which predicts terminal and spur leaf emergence of sour cherry (Prunus cerasus L. cv. Montmorency) grown near East Lansing, Michigan was developed from biological and temperature observations made in orchards near Egg Harbor, Wisconsin. Leaf number of spur and terminal shoots was more highly correlated with degree-day accumulation at a base of 4°C starting April 19, than with time. Leaf number on individual shoots was linear with respect to degree-day accumulation; however, not all growth on an individual tree was synchronous, and the plot of average leaf number vs. time was slightly curvilinear. Terminal buds set about 350 and 850 degree-days after first leaf emergence for spur and terminal shoots, respectively, regardless of location. Leaf size increased linearly with degree-day accumulation until full leaf expansion. At maturity terminal leaves were about 50% larger in area than spur leaves. Foliage growth was greatest during stage I and early stage II of fruit growth, and may compete with the fruit for assimilates needed for growth.
Vernalization and growing degree-day requirements of Thalictrum delavayi `Hewitt's Double' were determined to improve the production scheduling of this cut flower crop. Two-year-old crowns of T. delavayi `Hewitt's Double', lifted in the fall, were exposed to cold storage for 0, 3, 6, 9, 12, or 15 weeks at 8 ± 1°C. After storage, the containerized plants were grown at Massey Univ., Palmerston North (40°20.S) in a greenhouse heated at 15°C and vented at 20°C, under a natural photoperiod (11 h increasing to 13 h) plus a 4-h night interruption between 2200 and 0200 HR. As buds continued to develop during storage at 8°C, growing degree-days calculations were made over both storage and greenhouse forcing periods. All plants flowered, but T. delavayi `Hewitt's Double' nevertheless showed a quantitative vernalization requirement, being fully saturated after 6 weeks of cold storage at 8°C. With a base temperature of 0°C, time to flowering reduced from 3338 degree-days without vernalization to an average 2804 degree-days subsequent to the saturation of the vernalization response (6 to 15 weeks of vernalization). Flower yield averaged between three and five stems per plant, with stem lengths ranging between 140 and 200 cm. Differences in flower yield and quality among storage durations were minor and not commercially significant.
Vernalization and growing degree-day (GDD) requirements of Thalictrum delavayi Franch. `Hewitt's Double' were investigated by exposing crowns to cold storage for 0, 3, 6, 9, 12, or 15 weeks at 8 °C, and subsequently planting in a heated greenhouse under long-day conditions. Cumulative vernalization of crowns was complete after 6 weeks of cold storage at 8 °C. The time to flower, including time at 8 °C, was 3338 GDD (base temperature of 0 °C) without vernalization and 2802 GDD after complete vernalization. Commercial recommendations for rapid and predictable flowering of T. delavayi `Hewitt's Double' should include cold storage of crowns for a minimum of 6 weeks at 8 °C as part of the 2802 GDD during vernalization and forcing.
Methods Growing degree-day model development. Containerized plants of S. multiflorus subsp. katharinae were delivered to Massey University (Palmerston North, New Zealand; 40°20′S) on 5 Sept. 2002. The 63 plants each comprised a grade size of
time. Growing degree-day (GDD) units often are used to predict different plant developmental stages and may be a better means of establishing planting times than arbitrary dates. Temperature can be used with confidence to predict a plant's development
A simulation model for determining flower bud phenological stages and fruit growth as a function of daily maximum and minimum temperatures was developed for `Montmorency' sour cherry (Prunus cerasus L.). The models were developed and tested with observations collected in the three major sour cherry production areas in Michigan located in northwestern, western central, and southwestern sections of the lower peninsula. Observations of flower bud phenology and fruit diameter were collected at 3- to 7-day intervals, in spurs and terminal shoots across multiple years. Nonlinear equations using accumulation of growing degree-days (base 4 °C) as an independent variable were fitted to observed flower bud phenological stages and fruit diameter, expressed as percentage of final fruit diameter. Simulated bud phenology stages were in agreement with observed data. Mean differences of simulated vs. observed dates of early phenological stages in the three production areas were between 4 and 1 days for side green and near 0 days for tight cluster, while during later stages (e.g., first bloom and full bloom) mean differences ranged from -2 to 0 days. Means differences of predicted fruit diameter were in the range of 0 to -3 days. Needing only daily temperature data, these simulation models have potential applicability in improving the timing and efficiency of management decisions related to crop phenology, such as pest control, fertilization, and irrigation.
Subjection of intensively managed creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.). Farw., (syn. Agrostis palustris Huds.)] to supraoptimal soil temperatures is deleterious to root viability and longevity. The ability to estimate viable root length would enable creeping bentgrass managers to more accurately schedule certain management practices. The purpose of this rhizotron study was to develop a model, based on an accumulated degree-day (ADD) method, capable of estimating viable root length density of established `Crenshaw' and `L93' creeping bentgrass maintained under putting green conditions. Viable root length density observations were made biweekly and soil temperature data collected April through September 1997, and January through August 1998 and 1999. Relative viable root length density (RVRLD) is defined as the measured viable root length density divided by the maximum density attained that spring. In both years, maximum annual viable root length density for all plots was reached, on average, by 138 days from the beginning of the year (18 May). Cultivar and year effects were nonsignificant (P = 0.67 and 0.20, respectively). Degree-day heat units were calculated using an array of base temperatures by integral and arithmetical methods. Although the two accumulative methods proved suitable, the model regressing arithmetical degree-day accumulations against the bentgrass RVRLD provided a better fit to the data set. Use of the 10 °C base temperature in the arithmetical ADD calculations provided the following model; RVRLD = 0.98 - [1.30 × 10-4 (ADD)], accounting for 83.8% of the experimental variability (P < 0.0001). As several abiotic/edaphic factors have been shown to significantly influence root growth and viability, development of a widely usable model would include additional factors.
The heat-unit system, involving the sum of daily mean temperatures above a given base temperature, is used with processing pea (Pisum sativum L.) to predict relative maturity during the growing season and to schedule planting dates based on average temperature data. The Quebec pea processing industry uses a base temperature of 5 °C to compute growing-degree days (GDD) between sowing and maturity. This study was initiated to verify if the current model, which uses a base temperature of 5 °C, can be improved to predict maturity in Quebec. Four pea cultivars, `Bolero', `Rally', `Flair', and `Kriter', were grown between 1985 and 1997 on an experimental farm in Quebec. For all cultivars, when using a limited number of years, a base temperature between 0.0 and 0.8 °C reduced the coefficient of variation (cv) as compared with 5.0 °C, indicating that the base temperature used commercially is probably not the most appropriate for Quebec climatic conditions. The division of the developmental period into different stages (sowing until emergence, emergence until flowering, and flowering until maturity) was also investigated for some years. Use of base temperatures specific for each crop phase did not improve the prediction of maturity when compared with the use of an overall base temperature. All years for a given cultivar were then used to determine the base temperature with the lowest cv for predicting the time from sowing to maturity. A base temperature from 0 to 5 °C was generally adequate for all cultivars, and a common base temperature of 3.0 °C was selected for all cultivars. For the years and cultivars used in this study, the computation of GDD with a base temperature of 3 °C gave an overall prediction of maturity of 2.0, 2.4, 2.2, and 2.5 days based on the average of the absolute values of the differences for the cultivars Bolero, Rally, Flair, and Kriter, respectively.