Measurement of light interception by navel orange orchard canopies: Case study of Lindsay, California

Photosynthetically active radiation (PAR) intercepted by orange orchards (Frost Nucellar navel) having different canopy sizes was measured to determine the relationships with crop coefficient (K-co and K-cr) values and crop evapotranspiration (ET) (ETc). Three separate experiments were carried out near Lindsay, Calif. during the months of July and August 2004 to compute the fraction of light PAR intercepted by mature and immature orange orchards. Periodic readings of PAR data were compared with near simultaneous measurements of net radiation R-n (mV), heat transfer through exposed flux plates F-h (mV), and incident total solar radiation R-s (mV). The PAR data were used to calculate canopy light interception and the results were compared with those computed from the F-h and R-s data. The other sensors were studied as possible substitutes for the more expensive PAR light bar. Light interception by the different canopies was related to crop coefficient (K-co and K-cr) values that were determined by micrometeorological measurement of ETc and Penman-Monteith reference evapotranspiration ETo and ETr.