Seasonal variation in the radiation regime of a dwarf apple orchard

Abstract

Seasonal and daily radiation fluxes showed that the highest monthly albedo was 0.81 in January compared with a growing season mean of about 0.20. These differences correspond to dramatic changes in the surface characteristics with season. Patterns in photosynthetically active radiation were similar to those for incoming solar irradiance. The highest values of incoming long-wave radiation were on days with high temperatures and overcast skies, whereas outgoing long-wave radiation exhibited a midwinter minimum in January corresponding to a cold snow-covered surface. Net radiation was negative in the winter months but increased almost linearly in the late winter, spring, and early summer months. An understanding of these components of the radiation regime which drive the photosynthetic system may be useful in assessing winter injury or crop development during the growing season.