Evaporation Rates of Capillary-Watered Tomatoes in an East-West Glasshouse

Abstract

SummaryCapillary-watered beds 71 ft. long, 25 in. wide and 7 in. deep were installed at six positions across the width of the west half of a tenth-acre, east-west orientated, vinery glasshouse in order to measure the spatial variation in the daily evaporation rates of a tomato crop. Each bed was equipped with a separately metered water supply so that, assuming there was no drainage or leakage, a daily change in meter reading represented the loss by evaporation.From planting out in early March until mid-April there was little variation in daily evaporation rates across the width of the house. The variation increased as the crop grew in height and was greatest on bright sunny days and least on dull cloudy days. Maximum variation was registered on a bright sunny day in early May when the southernmost bed lost 23% more, and the northern beds from 5 to 11% less, than the mean daily evaporation rate.The extent of the variation in space and time emphasized the difficulty of determining when and how much water to apply to surface-irrigated crops and the advantage of capillary watering in supplying each plant with its precise requirement.