Towards predicting pesticide deposition from plant phenology; a study in spring barley

Abstract

The relationship between crop architecture and spray interception was investigated in spring barley at two developmental stages. Height and outer surface area were determined for stems, leaves and ears, when present. To trace the droplet interception by the crop a fluorescent dye was used. To avoid difficulties in measuring spray deposition on plant surfaces, the non-intercepted pesticide at different heights in the air between the plants was determined from the deposit on glass strips placed horizontally at different crop strata. A regression model was used to relate the glass strip measurements to the plant surface measurements. Analysis of the crop architecture indicated that the position and size of the leaves, the stem thickness and stem surface could all be described as a function of the height of the flag leaf. Analysis of deposition measurements showed that stems, leaves and ears all contributed significantly to spray interception, which correlated in a log-linear way with plant surface. The plant surfaces of stems, leaves and ears showed no significant differences in the fractions of droplets that were captured per unit of surface area, which fraction was indicated as the ‘k value’. This showed that the droplet interception in spring barley could, in principle, be modelled using a single coefficient. As a one-parameter model would restrict interpretability and comparability of the present results with other studies, the approach with separate k values was nevertheless preferred when analysing the deposition pattern in the crop and on the soil. The prospects of using crop height as the main model parameter for crop architecture in future predictions of pesticide deposition in cereals are discussed. © 1998 SCI