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Abstract: The evaporation of water in mushroom growing houses is rarely, if ever, measured on the majority of commercial farms. STOREY (1971, 1974) used a Piché evaporimeter to measure evaporative losses in mushroom houses and found that, where humidity was not controlled, the rate of evaporation of water varied with time of year and was related to the outside air temperature and dewpoint. He presented data to show that a low evaporation rate encouraged the development of disease (Mycogone perniciosa) and was associated with reduced cropping. Under the conditions he was studying, a daily rate of evaporation corresponding to a loss of 10 mm from a Piché evaporimeter seemed best for mushroom production. Both GERRITS (1968) and FLEGG (1974) have found that the rate of evaporation from the casing layer is an important factor affecting the water requirement of the crop. GERRITS concluded that replacement of the water lost by evaporation is the main purpose of watering, but FLEGG included other factors as well as evaporation loss in his equation for calculating the quantity of water required by the crop. This paper examines the Piché evaporimeter as a practical means of assessing the evaporative conditions in a mushroom house and of estimating the loss of water from the casing layer thus facilitating the water management of the crop.
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