Showing papers by "John L. Monteith published in 1986"
TL;DR: For a stand of winter wheat, radiative canopy temperature measured with an infra-red radiometer was systematically related to a surface temperature derived from air temperature and wind speed profiles.
Abstract: For a stand of winter wheat, radiative canopy temperature measured with an infra-red radiometer was systematically related to a surface temperature derived from air temperature and wind speed profiles. Radiative temperature changed significantly with viewing angle and azimuth, but the influences of sun angle and ground cover were minimised by inclining the radiometer at 55 ° to the vertical and at right angles to the solar beam.
182 citations
TL;DR: The supply of water provided by the root system of a crop stand is defined in terms of the rate at which water is extracted by a root front moving downwards with a constant velocity, the available water per unit soil volume, and a time constant that is inversely proportional to root density.
Abstract: The supply of water provided by the root system of a crop stand is defined in terms of the rate at which water is extracted by a root front moving downwards with a constant velocity, the available water per unit soil volume, and a time constant that is inversely proportional to root density. The demand for water, often identified with a potential transpiration rate, is defined in terms of a maximum crop growth rate multiplied by the conservative ratio of transpiration to dry-matter production. From experimental evidence, supported by theory, this ratio is proportional to the mean saturation vapour-pressure deficit. As hypothesized, the root front accelerates during seedling establishment to keep demand and supply in balance. Once a maximum root velocity is reached ( ca . 2-4 cm d -1 ) transpiration is limited by water supply, except when the soil behind the root front is wetted by rain or irrigation, when it is limited by demand. Irrigation amounts and timing can both be estimated from this scheme.
181 citations
TL;DR: In this article, the authors measured the radiative heat fluxes between plastic sheet mulches and the soil surface, and found that reflective mulches may reduce the diurnal amplitude of soil temperature, and always reduce the radiant heat gain by the soil.
171 citations
TL;DR: In this paper, the authors extended the Penman-Monteith equation for transpiration from a uniform stand of vegetation to take account of the response of stomata to the saturation deficit (SD) of air in the canopy.
77 citations
TL;DR: In this paper, the mean daytime saturation vapour pressure deficit (D), measured at screen height, decreases from a maximum of 3-4 kPa attained several months before rain arrives to a minimum of 0.5-1 kPa in the month of highest rainfall.
Abstract: In monsoon climates, the mean daytime saturation vapour pressure deficit (D), measured at screen height, decreases from a maximum of 3–4 kPa attained several months before rain arrives to a minimum of 0.5–1 kPa in the month of highest rainfall. Climatic records from India and West Africa were analysed to give the relation between D and precipitation (P mm month −1 ) as: where n ranged from 0.5 to 0.9 between stations. The dependence of dry matter production on D and therefore on P is evaluated when growth is restricted by rain and when this restriction is removed by irrigation. In the first case, the decrease in demand for water associated with a decrease in D is comparable in importance with the increase of water supply (P). The analysis has implications for the marginal response of crops to supplemental irrigation and for the interpretation of experiments with a line-source or rain-shelter.
15 citations
4 citations