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Plastic-mulched Bed Temperature Extremes are Affected by Irrigation Method and Crop Canopy

On-going studies at GCREC-Bradenton investigating the influence of irrigation system and plant canopy development on soil bed temperatures are showing some very interesting results.  These studies are part of an overall effort to develop predictive models which use bed temperature, soil moisture content, and environmental factors to simulate soil-applied agric-chemical movement and dissipation in a production bed.

Plots were set up to measure temperatures in a grid fashion at 32 locations down to depths of 16 inches from the surface of each bed at 12 different sites including drip-irrigated and seepage-irrigated beds (east-west orientation) with and without tomato plants throughout the past 3 growing seasons.  Thermocouples attached to logging devices measured temperatures every 15 minutes to see how bed temperature distribution changed through each day during each season.  As an example, for mid-afternoon on May 11, 2003, bed temperatures for drip-irrigated tomatoes varied from 124°F (51°C) at the south bed shoulder just under the plastic to 84°F (29°C) at 8 inches from the surface in the bed center when the air temperature reached 74°F (23°C).  On the same day at the same time, seepage-irrigated tomatoes showed temperatures of 107°F (42°C) at the bed shoulder and 84°F (29°C) at 8 inches from the surface in the bed center.  Observations of temperature changes throughout the day indicated that seepage-irrigated beds generally showed lower temperatures at similar bed locations at the same time of day and cooled off more quickly during evening hours when compared to drip-irrigated beds.  This was probably due to continuous replenishing of soil moisture from the cooler water table for seepage irrigation. 

While this information is being collected for model development purposes, the data show the extreme temperatures that can be measured in the soil bed.  Bed surface temperatures, especially for fall-crop tomatoes and peppers, must be considered to prevent excessive heat conditions for newly-set transplants.  As expected, the maximum temperatures were generally measured at mid-afternoon so it would be recommended that, where possible, transplanting should be done in the morning hours to minimize transplant shock.  Examples of bed temperature distribution (also showing thermocouple location) at 3 times of the day (May 11, 2003) are shown in the figure (click here) (temperatures in °C).

Any questions or comments on this information can be directed to Craig Stanley, GCREC-Bradenton, 941-751-7636 ext 248 (cds@mail.ifas.ufl.edu).

(Craig Stanley, professor, GCREC-Bradenton - Vegetarian 04-04)