Distribution of Diffuse UV-B Radiation in a Maize Canopy

Maize (Zea mays L.) plants respond to ultraviolet-B (UV-B) radiation elevated from ambient solar levels with decreased photosynthesis, delayed onset of flowering and grain filling, and ultimately reduced maize crop yields. One potentially UV-sensitive organ of maize is the silk. The penetration of UV radiation through the canopy varies with sky condition canopy condition, and solar zenith angle; resulting in varying proportions of UV radiation incident on leaves and silks. This study was designed to evaluate the radiative environment of the maize canopy in the UV waveband and determine the UV exposure of corn silks and leaves under ambient conditions and conditions under a changing climate. The solar UV radiation in a maize canopy was measured during the summers of 2004 and 2005 using a portable ultraviolet multi-filter rotating shadow band radiometer (UV-MFRSR). In-canopy measurements were compared to the UV-MFRSR at the West Lafayette UV-B Climate Monitoring Station to determine the penetration of UV through the canopy. Canopy view factors were determined from hemispherical photography. The UV-MFRSR measures the diffuse and global solar irradiance in seven narrow (2 nm nominal FWHM bandwidth) wavebands at nominal center wavelengths of 300-, 305-, 311-, 317-, 325-, 332-, and 368- nm. Measurements were used to estimate the shade and sunlit UV irradiance throughout the upper half of the canopy and at the silking height in particular as functions of the solar zenith angle, cloud cover, sky view, and canopy cover. Infleucne of changes in cloud cover and ozone column depth on the UV exposure of silks is evaluated.