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Accueil du site → Doctorat → Royaume-Uni → 1989 → Water use of the alfalfa crop under desert conditions in Saudi Arabia

University of Edinburgh (1989)

Water use of the alfalfa crop under desert conditions in Saudi Arabia

Alyemeny, Mohammed N.

Titre : Water use of the alfalfa crop under desert conditions in Saudi Arabia.

Auteur : Alyemeny, Mohammed N.

Université de soutenance : University of Edinburgh

Grade : Doctor of Philosophy (PhD) 1989

Résumé
The aim was to investigate the water use of Medicago sativa L. in an irrigated agricultural system in Saudi Arabia using three different techniques : (i) Bowen ratio method ; (ii) a method relying on the energy balance of leaves ; and (iii) the use of a laboratory measurement system to provide the physiological parameters that enable a modelling approach to be used. The climate of the nearby desert is characterised by high albedo (0.40), low water vapour pressure (&#60 10&#37 RH) and high temperature decreased by im6oC., and the vapour pressure increased by 2.0kPa. Crop albedo varied diurnally and seasonally and was much lower than the desert. Net radiation over the crop was a near-linear function of short-wave irradiance. Analysis of the diurnal microclimate of the two irrigation types (surface irrigation and spray) indicates slight differences. The sources of the differences may be related to the scale of the field size and the irrigation frequency. The Bowen Ratio method was used to estimate water use by the crop. The equipment was placed well in from the leading edge of the field (150 h). The Bowen Ratio was in the range -0.5 to 0.5. An examination of probable errors suggested that the technique is close to the limit of its applicability in this case, but it nevertheless provides an estimate of day time evaporation to within 20&#37. The daily total of evapotranspiration in the summer months was in the range of 9-15 mm day-1. Water use by a sample of leaves at the top of the canopy was assessed. It was clear that the leaf energy balance method can be used to track stomatal conductance and thus indicate times of atmospheric stress indicated by stomatal closure. The maximal stomatal conductance was 3.5 cm s-1 and the corresponding maximal leaf surface transpiration rate was 800 Wm-2. A type of error analysis was devised to explore the effect of making errors in the measurement of the important variables. It was concluded that the technique was most useful between 09.00 and 15.00 h, when the probable error was about 20&#37. Gas exchange in the laboratory provided light response curves of photosynthetic rate and stomatal conductance. Maximal photosynthesis was 22-32 mol m-2s-1, but light-saturation did not always occur even a photon flux density of 1800 mol m-2s-1. The stomatal conductance was only weakly dependent on leaf-air vapour pressure deficit and the maximal value was 600 mmol m-2s-1. In the dark, there was a considerable conductance, suggesting a possible importance of nocturnal transpiration.

Mots Clés : Botany Botany Agronomy Plant diseases Horticulture Agricultural engineering Botany Agronomy Agricultural engineering

Présentation : EThOS (UK)

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