COMPARISON OF 4 METHODS FOR ESTIMATING TOTAL LIGHT INTERCEPTION BY APPLE-TREES OF VARYING FORMS

Four methods of estimating daily light interception (fisheye photograp hy with image analysis, multiple-light sensors, ceptometer, and point grid) were compared using various apple (Malus domestica Borkh.) tree forms: slender spindle, Y- and T-trellises, and vertical palmette. Int eractions of tree form, time of day, and atmospheric conditions with l ight interception estimates were examined. All methods were highly cor related to each other (r(2)>0.92) for estimated daily mean percent tot al light interception by the various tree forms, except that the point grid method values were slightly lower. Interactions were found among tree form, time of day, and diffuse/direct radiation balance on estim ated light interception, suggesting that several readings over the day are needed under clear skies, especially in upright canopies. The sim ilar results obtained by using the point grid method (counting shaded/ exposed points on a grid under the canopy) on clear days may allow rap id, simple, and inexpensive estimates of orchard light interception.