Determination of head lettuce crop coefficient and water use in central Arizona
AuthorOliveira, Aureo Silva, 1965-
AdvisorMartin, Edward C.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe assessment of crop evapotranspiration (ET) has received intensive research due to its critical role in irrigation management and water conservation studies. Because weather conditions largely determine ET, various methods based on meteorological factors have been developed to estimate ET rates. In order to accommodate the concept of reference crop ET (ETo), evaluation of weather data quality has been addressed. In this research, 9 year (1989-1997) weather data from the AZMET weather station at the Maricopa Agricultural Center were used to compare daily and 10 day average ETo estimated by the Hargreaves (HARG), FAO 24 Penman (FAOP), and FAO Penman-Monteith (FAOPM) methods. Before ET calculation, the weather data were evaluated for the influence of aridity at the weather station site and sensor calibration/malfunctioning problems. Corrections were made on temperature and solar radiation data. Reference ET as reported by the AZMET was also considered for comparison purposes. In general, the weather data correction decreased ETo estimates 18.3%, on average. The highest reduction (23.5%) was obtained with the FAOPM method. When this method was used as the standard for ETo estimate comparison, the FAOP method corrected for site aridity ranked first as predictor of ETo despite its tendency for overestimation. At the Maricopa Agricultural Center, a two year field research (Fall-Winter of 1996/97 and 1997/98) was carried out to derive head lettuce (Lactuca sativa L.) crop coefficient (Kc) and to investigate the effects of ETo method in the shape and values of the crop coefficient curve. For the periods of low crop ET, the 2 year (Kc) from the HARG, FAOP, and FAOPM methods did not differ significantly. However, in the peak demand period, crop coefficients derived from the three methods peaked at different values. The predicted peak (Kc) was 0.87, 0.72, and 0.82 for the HARG, FAOP, and FAOPM methods, respectively. These results reflect the tendency of ETo underestimation by the HARG method and overestimation by the FAOP method under and conditions. Crop coefficients derived in the 96/97 growing season were then used to investigate the effects of (Kc) and ETo mismatching in the water use and yield of lettuce during the 97/98 growing season. To reach such objectives, an experiment design in Latin square with four replications and four treatments was carried out. Differences in seasonal water depth were as high as 33 mm among treatments. The analysis of variance revealed that the treatments did not induce lettuce marketable yield statistically different at the 5% significance level.
Degree ProgramGraduate College
Agricultural & Biosystems Engineering