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Accueil du site Doctorat États-Unis 1988 Alfalfa productivity and temperature : an application of equivalent hours of maximum net photosynthesis methodology

**Titre : ** Alfalfa productivity and temperature : an application of equivalent hours of maximum net photosynthesis methodology

**Auteur : ** Sherrill, Daniel Edward

**Université de soutenance :** University of California, Los Angeles,

** Grade : ** Doctor of Philosophy (PhD) 1988

**Résumé **

A monthly climatic index, equivalent hours of maximum net photosynthesis, that measures favorability of the thermal environment for plant photosynthesis, was adapted for the purpose of alfalfa yield prediction. The index uses a curve characterized by an optimum, a lower threshold, and upper threshold temperatures, to define ideal thermal conditions for a particular plant. A radiation factor is also included. Equivalent hours measures how much a climatic regime adheres to that thermal ideal and radiation response. The adaptation involved simulation of daily temperatures and calculation of daily equivalent hours. Alfalfa yields from experimental plots in California and other states were regressed against equivalent hours per cutting period and per day. Results per cutting period indicate that : Optima for alfalfa are higher than generally reported in the literature, temperature optima can be identified by the modified procedure, alfalfa experiences acclimatization during the cutting period, a correction factor for cloudiness gives inconsistent results, and a minimum number of observations are necessary (approximately 15-20) to establish a consistent relationship between equivalent hours and yield at a particular site. Results per day give the same optima as the per period analysis but with higher correlation coefficient. Acclimatization is demonstrated in alfalfa cultivars at three California sites. These sites, Davis, Westside Field Station, and Imperial Valley are used to develop a general model that incorporates acclimatization. The general model assumes acclimatization can be represented by a hyperbolic relationship between optimum temperature for the index and average maximum temperature during the cutting period. Thresholds are assumed to be a definite number of degrees above and below the optimum. Equivalent hours are calculated using the optimum based on the acclimatization relationship. Crop growth rate is predicted using the following relationship : Crop growth rate (1bs per acre per day) = 22 X equivalent hours per day - 68.7 Alfalfa yield predictions were also tested using models based on growing degree-days and solar radiation. The general model gives more consistent results than either a radiation or growing degree-day model.

**Sujets :** Plant growth/Grasses/Lucerne/Photosynthesis/Alfalfa USE Lucerne/ ;

Page publiée le 26 décembre 2016