Vapour-pressure deficit the plant may dry out and die. For this reason the ideal range for VPD in a greenhouse is from 0.45 kPa to 1.25 kPa, ideally sitting at around 0.85 kPa. As a general rule, most plants grow well at VPDs of between 0.8 and 0.95 kPa. In ecology, it is the difference between the actual water vapour pressure and the saturation water vapour pressure at a particular temperature. Unlike relative humidity, vapour-pressure deficit has a simple nearly straight-line relationship to the rate of evapotranspiration and other measures of evaporation. To compute the VPD, we need the ambient (greenhouse) air
Economics terminology that differs from common usage Economics terminology that differs from common usage In any technical subject, words commonly used in everyday life acquire very specific technical meanings, and confusion can arise when someone is uncertain of the intended meaning of a word. This article explains the differences in meaning between some technical terms used in economics and the corresponding terms in everyday usage. Economists commonly use the term "recession" to mean either a period of two successive calendar quarters each having negative growth of real gross domestic product—that is, of the total amount of goods and services produced within a country—or that provided by the