Development and assessment of a mathematical model to predict foliar spray deposition under laboratory track spraying conditions

Abstract

AbstractA mathematical model based on Young's equation of adhesion of liquids to solid surfaces has been developed to predict foliar spray deposition under track‐spraying conditions. The model incorporates the physical nature and morphological characteristics of the plant leaf surface and the physical properties of the spray solution. It was tested using experimental spray deposition measurements on four different plant species and an artificial target of glass rods with an array of forty‐eight solutions varying systematically in composition and properties. The morphological factors and regression coefficient of the model were calculated by a least‐squares multiple‐regression analysis of the observed spray deposition. The physical natures, wettabilities, of the target surfaces were estimated from contact angle measurements. The physical properties of the spray solutions, drop sizes and dynamic surface tensions were measured by a Malvern 2600 HSD particle size analyser and the maximum bubble pressure method respectively. Drop sizes were approximately constant through the series of solutions though dynamic surface tensions varied and form an important term in the model.The spray depositions predicted by the model were plotted as response surfaces against solution composition and compared with those from the observed spray depositions. Agreements were high (explained variances, wheat, 96.4%; green foxtail, 98.6%; pea, 98.9%; sugar beet, 98.6%; glass rods, 99.4%), giving confidence that the model had been correctly formulated.An explanation for the varying abilities of different plants to capture different volumes of spray solutions can now be expressed in qualitative and quantitative terms. Further validation of the model is in progress.