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  • Author or Editor: J. David Martsolf x
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Abstract

The color-coded thermal map of the Florida peninsula on the cover is a satellite view of the January 13, 1981 freeze, one of the two most disastrous freezes of this century. The map is a product of the Satellite Frost Forecast System (SFFS) developed by the Institute of Food and Agricultural Sciences of the University of Florida with support from the National Aeronautics and Space Administration. SFFS acquires temperatures sensed by the GOES-EAST satellite from the National Oceanic and Atmospheric Administration (NOAA) facilities in Suitland, Md., through an automated telephone link (see insert). Instructions within the mini-computer, the heart of SFFS, partition the temperature data into color bands and cause the resulting map to be displayed on a color TV screen within minutes of the reception of the satellite data. Currently, NOAA sectorizes the infrared satellite data, i.e., partitions the Florida peninsula data from that for the hemisphere, and moves it to a separate queue from which SFFS acquires it by a telephone call that requires about 3 minutes per map.

Open Access

An undertree sprinkler [Maxijet] irrigation system designed to deliver 42 to 80 l/hr to each of 570 citrus trees (planted 6.1 × 6.1 m, heights of the larger uniform trees: 2m) was fed through an irrigation water heater [Aquaheet]. The heater added up to a megawatt of heat to the irrigation pipeline by the combustion of diesel fuel. A porous orchard cover (59m × 64m × 3.6m; 0.38ha) sheltered one of six plots of similar size in a citrus orchard on the University of Florida campus in Gainesville. Two border zones, one 3 rows deep on the north border and one on the west tapering from 2 rows on the north to a single row on the south end reduce the edge effect for a total orchard area of 2.12 ha. A minicomputer based data acquisition system provided observations of temperature, wind speed and direction made as frequently as one scan per minute. The effect of the orchard cover, the undertree irrigation, the heated irrigation and combinations of these three methods on the orchard microclimate will be shown in graphs and diagrams of observations taken during the freezes of February 24-26, and December 24-25, 1989. A diagram of the potential effect of water temperature on latent heat transport in the orchard will be discussed as will be problems with documentation of dew point temperature with chilled mirrors under freezing conditions.

Free access

An undertree sprinkler [Maxijet] irrigation system designed to deliver 42 to 80 l/hr to each of 570 citrus trees (planted 6.1 × 6.1 m, heights of the larger uniform trees: 2m) was fed through an irrigation water heater [Aquaheet]. The heater added up to a megawatt of heat to the irrigation pipeline by the combustion of diesel fuel. A porous orchard cover (59m × 64m × 3.6m; 0.38ha) sheltered one of six plots of similar size in a citrus orchard on the University of Florida campus in Gainesville. Two border zones, one 3 rows deep on the north border and one on the west tapering from 2 rows on the north to a single row on the south end reduce the edge effect for a total orchard area of 2.12 ha. A minicomputer based data acquisition system provided observations of temperature, wind speed and direction made as frequently as one scan per minute. The effect of the orchard cover, the undertree irrigation, the heated irrigation and combinations of these three methods on the orchard microclimate will be shown in graphs and diagrams of observations taken during the freezes of February 24-26, and December 24-25, 1989. A diagram of the potential effect of water temperature on latent heat transport in the orchard will be discussed as will be problems with documentation of dew point temperature with chilled mirrors under freezing conditions.

Free access

Observing plant damage following a frost or freeze is perhaps the oldest and likely one of the most frequently used methods by horticulturists to assess relative merits of protection methods. To facilitate that method, a citrus orchard of 66 Ambersweet on Sour Orange, 198 Orlando Tangelo and 197 Robinson tangerine, the latter two varieties on Carrizo Citrange, was planted in early April of 1990, on the main campus of UF. The variety rows run the N-S with trees separated by 4.6m. The 11 different sprinkling treatments run E-W with separations of 6.1m. When 461 sprinklers are utilized the well delivers rates up to 60 l/hr/nozzle. A visitor can walk a N_S middle and view each treatment on a particular variety in series. During the winter of 90-91, half the trees had conventional under-tree sprinklers while the other half had various types of in-tree sprinklers. Following an advective freeze, Feb. 15-17, 32% of the trees with in-tree sprinklers had broken limbs compared with 4% of those with under-tree sprinklers. But estimates of canopy damage indicated less difference between the treatments, and measurements of tree height before and after freezes were so variable that significant differences were not apparent. Observations following mild freezes in 91-92 indicated high variability in the effects of a particular method on individual trees. Problems in the development of a tree imaging technique using a still image video camera [Cannon RC-250] and the use of such observations in refining mechanismal models are highlighted.

Free access

Abstract

Observations of horizontal and vertical components of net radiant loss, radiation divergence, from an orchard heated for frost protection using fixed and traversed net pyrradiomeiers are presented. The horizontal loss or flux through the orchard sides becomes significant as the area occupied by the orchard becomes less than 5 ha and as border heating is concentrated. The vertical loss, or loss through the top minus the input through the bottom, is shown to double (from approximately 2.5 to 5mWcm-2) during periods fired at typical rates. These observations suggest possible refinements of the radiation components of models and focus attention on the direct radiant loss from heaters. Some techniques that may result in conservation of heating fuel are suggested.

Open Access

Abstract

The development of an equation describing a 3-dimensional energy budget of a crop volume from conservation of energy and mass equations is presented. The terms of the equation are interpreted for orchard frost protection studies.

Open Access

Abstract

Aluminum-foil-surfaced shields were evaluated with individual citrus trees. These shields, highly reflective in the infrared, moderated leaf temperatures by interrupting their radiant heat loss. A horizontal shield over an individual tree provided about 1°F of cold protection on clear and relatively calm nights. Temperatures of shielded and unshielded leaves were not affected by moderate wind drift or position on the tree. Radiant cooling may induce air flow over the tree that tends to convectively equalize leaf and air temperature. Large differences did not occur between leaf temperatures on adjacent trees. Neither position nor replication produced large temperature differences between leaves at night. Analysis of the heat balance in quasi-steady state indicated that 1° differences were reasonable and that small radiation shields cannot be expected to provide more protection than the amount that leaves are radiantly cooled below air temperature.

Open Access

Abstract

Adjustment of the sprinkling application rate to existing atmospheric conditions to conserve water may be accomplished by turning systems on and off. The maximum off period that is tolerable is calculated. It is the sum of time required to freeze the applied water plus time during which the ice coated plant parts cool to the critical temperature. Values of the off period for typical frost conditions are proportional to wind speed and wet bulb temperature. Field test results indicate intermittent sprinkling provides a method to reduce water consumption in sprinkling for frost protection.

Open Access

Abstract

Tree trunks painted on the sunlit side with white exterior latex paint were found to be 30 C cooler than nonpainted trunks during midwinter in midlatitudes. The dependency of the cambium temp amelioration on wind speed and trunk diam is indicated through an argument based on convective transfer theory. The argument suggests that for trunks larger than 10 cm diam or for wind speeds less than 30 cm/sec around the trunk or both, the amelioration due to white paint may be greater than 30 C.

Open Access

Abstract

The radiant fractions of four currently available orchard heaters (spot, large cone, return stack and auto clean stack) were determined under orchard conditions using observed surface temperatures, emissivity and the Stefan-Boltzmann Law. The contribution of the flame extending above the spot heater stack to its total radiant output was determined. Stack surface temperatures increased with burning rate on the large cone, return stack and auto clean stack heaters but decreased on the spot heater. The position of the highest temperature was near the bottom of the large cone, return stack and auto clean stack heaters and near the top of the spot heater. Surface temperatures were lower in general on the spot heater than on the other three heaters. The radiant fractions of the large cone, return stack and auto clean stack heaters were greater than 20% and relatively constant with burning rate. Even though the flame contribution is purposely overestimated the radiant fraction of the spot heater was less than 16%. For low wind speeds under which most orchard heating occurs the effect of wind speed on the radiant fraction was negligible.

Open Access