The microclimate of the potato crop

Abstract

SUMMARYShade temperatures and humidities in a standard screen and at an arbitrary level of 15 cm in In dry sunny periods : potato crops were continuously recorded during three summers, 1947-49.(1) (2) (3) (4) the maximum temperature in the crop was from 0" to 13°F higher than in the screen, and over a period of eleven weeks in 1947 averaged 6°F higher ; the crop minimum was about 2°F lower than in the screen ; over a period of five weeks in 1949 the average daily mean temperature in the crop was 22°F higher than in the screen, and the average daily temperature range was 8°F greater than in the screen. Wind, wet soil and cloudy weather greatly reduced these contrasts ; occasionally the crop minimum was higher than the screen minimum.By day, humidity was higher in the crop than in the screen, the average difference at the minima being 5 per cent in relative humidity, and 7°F in dew point. By night, the dew point in the crop was, on average, 2°F lower than in the screen, corresponding to the observed difference in mean minimum air temperatures.During 1948 and 1949, more precise discontinuous records were taken of temperature, humidity and wind speed in and above potato crops with different densities of foliage in a variety of weather conditions. Temperature and humidity were measured at 10, 20 or 30, and 60 cm ; wind at 20, 30 and 200 cm above ground level. In the crop there was only a slight temperature gradient in the early morning and throughout cloudy days, but during sunny days gradients were produced, depending on crop density ; it was hottest at 10 cm in an open crop, at 30 cm in a dense crop ; in both it was usually coolest at 60 cm when the soil was dry, but over wet soil the lowest temperature was found at 10 cm. Except on cloudy days, temperature inversion took place before sunset whatever the foliage density or moistness of the soil.Humidity (dew point) was usually greatest at 10 cm, but in a dense crop over dry soil water vapour transpired from the leaves often caused the air at 30 cm to be more humid than that at 10 cm.Wind affected both temperature and humidity by increasing lapse rates and causing rapid fluctuations within the crop, particularly of humidity. Changes of wind speed within the crop took place every few seconds, the amplitude of the fluctuations depending on the speed of the wind above the crop.

An Analysis of Actual Evapotranspiration

“…This proposition is not allowed when calculating short term net longwave radiation, because then important differences in surface and air temperature can exist (ROBINSON, 1950;MONTEITH and SZEICZ, 1962). The highest surface temperatures occur generally in a short, open crop, which decreases strongly the movement of air near the surface (BROADBENT 1950). Data reported by MONTEITH and SZEICZ (1962), given in table 4, indicate that the mean temperature during 24 hours, of various cropped surfaces and air temperature measured in the screen do not differ very much.…”

Monitoring canopy and air temperature of dominant vegetation in tropical semi-arid using bioclimatic model

“…In general, the daily trend of air temperature in the canopy depends on the supply of solar radiation. The layer of leaves where the radiation is intercepted acts as a filter influencing the rate of long-wave radiation loss, the total absorbed energy used for evaporation of water from the soil, the plant transpiration intensity and the turbulent transport of heat in the canopy (Broadbent, 1950). The strata of the canopy that are subject to different and stronger thermal influences can have a greater acceleration of senescence in leaves exposed to higher temperatures (Jochum et al, 2007).…”

The impact of weather on life: As explored in the quarterly journal of the royal meteorological society

“…The QJ for 1950 contained two biological papers from Rothamsted: "Evaporation over the British Isles" by H. L. Penman (1950), a hydrological classic, and "The microclimate of the potato crop" by L. Broadbent (1950). Other related papers appeared throughout the 1950s, e.g.…”