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New tools for ET estimation and irrigation management in specialty crops

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131595001,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   Lee F. Johnson, Michael D. Cahn, Frank Martin, Forrest S. Melton, Chris P. Lund, Barry F. Farrara, Sharon Benzen
Keywords:   Crop evapotranspiration irrigation trials lettuce broccoli fractional cover crop coefficient.

Abstract. Accurate estimation of crop evapotranspiration (ETc) supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and maintenance of crop quality. Past research in California has revealed strong relationships between canopy fractional cover (Fc), crop coefficients (Kc), and ETc of specialty crops, while additional research has shown the potential of monitoring Fc by satellite remote sensing. Irrigation trials were performed on these crops during 2012 to compare irrigation scheduling by ET-based approaches (targeting 100% ET replacement) with current industry standard-practice. Each trial included three treatments with five replicates in a block randomized design. Two decision-support systems were evaluated as follows: 1) an FAO56-based algorithm under NASA's Satellite Information Management System, and 2) a U.C. Cooperative Extension on-line database driven irrigation scheduling tool, CropManage. Both methods utilized daily grass-reference ETo data from the California Irrigation Management Irrigation System (CIMIS) for weather-based irrigation scheduling. A third treatment was irrigated according to local standard practice, estimated at 150% ET replacement. Both decision-support treatments rendered approximately 30% reductions in applied water, with little-to-no impact on marketable yield. Cored head-trimmed lettuce yields were ca. 20 tons/ac across treatments, albeit with CropManage slightly though significantly (.10 level) lower possibly due to bird damage, yet still meeting industry standards. Broccoli yields were ca. 8 tons/ac for all treatments, with standard practice yields slightly though significantly (.10 level) below that for the reduced water treatments, possibly due to rootzone saturation or nutrient drainage to sub-rootzone. The experiments will be repeated during the 2013 growing season.

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