Light Interception and Soil Water Dynamics In Row Crops: A Two Dimensional Approach.

The architecture of row crops results in variable light interception by the crop and variable energy transmittance to the soil according to leaf density, the orientation of the crop rows and direction of sunlight. Generally, a daily radiation integral is sought for a given geometry and leaf area. Few of the studies have focused on light interception across plant rows as an endpoint. A few exceptions include recent studies by Annondale et al. (2004) and Oyarzun et al. (2007) where light dynamics in tree crops have been investigated. One dimensional models assume average values of light interception for the canopy as a whole and partition energy to the canopy and soil based on fixed geometries. The two-dimensional soil model 2DSOIL has been incorporated into two mechanistic crop models (corn and potato). Although diurnal effects of the changing sun path can be accounted for using a hedgerow model GLYCIM, (Acock et al, 1984),  only an average interrow light interception value is used. The objective of this study was to investigate two dimensional hourly light interception in row cropped corn and potato with the purpose of improving the light interception model to calculate detailed light interception within a plant row. Several row spacings and nitrogen levels over two years were used in field plots to obtain a range of light interception data. Intercepted light was measured using up to seven line quantum sensors in different configurations. The different canopy structures of corn and potato resulted in differences in radiation interception that varied over time. Average leaf area may be acceptable to calculate light interception in varied canopies if row orientation and solar angle are known. Maximum light interception by the canopy and soil varied as a function of row position and hour of day. The variance due to time varied over that of row position. These results were used to evaluate the 2DSOIL model as linked with the corn model MAIZSIM.