The Shade Bound: Where Shade Cloth Stops Paying for Lettuce in Hot Climates
Year: 2026
Type: article
Abstract: Shade cloth is widely sold and widely believed to help any crop in hot weather. This paper tests that belief for a stated case — lettuce, a heat-sensitive leafy crop — under stated assumptions: a saturating light response with half-saturation at a daily light integral of 12 mol/m2/d, a heat penalty of 4.5 percentage points per degree Celsius of peak leaf temperature above 28 °C, unshaded leaves running 4 °C above air, and shade cooling the peak leaf temperature by 6 °C per unit of shade fraction (1.8 °C at 30% shade, 3.0 °C at 50%, 4.2 °C at 70%). In a hot, bright season (daily light integral 45 mol/m2/d, peak air 38 °C) relative yield rises from 0.409 unshaded to a maximum of 0.463 at 40% shade in a fine scan, with 30% shade giving 0.457 and 50% giving 0.461, while 70% shade falls back to 0.414. In a hot but cloudy season the best shade is only about 25%, in a warm bright season 30% shade gains just 2.2%, and in mild or cool seasons no shade fraction pays at all: at peak air 28 °C every shade level reduces yield, by 26.8% at 70% shade. The popular claim that shade always helps in the heat does not survive as a general rule; it holds only where surplus light and severe heat coincide. This study is simulated, not measured.
Author: Aldred, William Alexander
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7225736919
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