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Title: Aerodynamic and crop resistances, growth, development and evapotranspiration of onion (Allium cepa L.) in semiarid Venezuela prediction
Author: Lopez Marquez, Jorge Luis
ISNI:       0000 0004 2742 9819
Awarding Body: University of Reading
Current Institution: University of Reading
Date of Award: 2012
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The growth, development and evapotranspiration of onions (Allium cepa L.) were studied on commercial crops grown under furrow irrigation in semiarid conditions at Quibor, Venezuela. Photoperiod, which only varied by 1.2 hours through the year, was the major environmental influence on crop development. The onset of bulbing in TG483, a "short day cultivar", took between 42 and 74 days from transplanting, taking longer in shorter photoperiods. Bulb yields of the crops varied between 11.3 to 18.3 t ha ˉ1, the latter from an intermediate hybrid "Utopia" transplanted at the end of March. Meteorological measurements were made within the crops. Wind profiles above the crops were measured in two plantings. The aerodynamic resistance to vapour transfer, derived from these profiles, showed a consistent decrease as the crop developed, varying from 340/U2 s m ˉ1 in the initial phase to 180/u2 s m ˉ1 near maturity (U2 is the windspeed at 2 m). Stomatal resistance, measured in three plantings showed relatively constant values (mean 1.7 s cm ˉ1). Crop (surface) resistance was estimated from stomatal resistance and leaf area index and decreased from transplanting to minimum values (52 to 99 s m ˉ1) during the mid to late season stages and increased slightly at maturity. There was good agreement between reference crop evapotranspiration estimated by the FAO-56 Penman-Monteith equation and by the pan evaporation method. Crop water requirements were estimated using the above resistances in the Penman-Monteith equation and by the FAO-56 method using crop coefficients. The latter gave greater values in the initial crop stage but lower values subsequently. Actual crop evapotranspiration was measured by a neutron probe and gravimetric samples in one planting. This agreed well with the Penman-Monteith estimates. Crop coefficients were calculated from the Penman- Monteith estimates and the actual values and compared to FAO coefficients. The one step method can provide good estimates of the actual crop water requirements.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available