Determining input values for a simple parametric model to estimate evaporation from vineyard soils with special reference to clay content and trellis system

Abstract

Estimating soil evaporation (E_s) is an important part of modelling vineyard evapotranspiration for irrigation purposes. Furthermore, quantification of possible soil texture and trellis effects is essential. Daily E_s from six topsoils packed into lysimeters was measured under grapevines on slanting and vertical trellises, respectively. Following irrigation, cumulative soil evaporation (∑E_s) from the bare, untilled soils over 14-day drying cycles was plotted against cumulative reference evapotranspiration (∑ET_o) to determine E_stransition from the constant rate stage (Stage 1) to the falling-rate stage (Stage 2). During Stages 1 and 2, rate of E_s is determined by atmospheric conditions and soil properties, respectively. Slopes of ∑E_s vs square root of ∑ET_o plots in Stage 2 provided the input constant (β value) for each soil. In Stage 1, ∑E_s was almost equal to ∑ET_o but the ratio varied as grapevine canopies developed. The β values varied between 2.15 ±0.09 mm^0.5 and 4.68 ± 0.14 mm^0.5 . The β values were best related to clay content (R² was 0.7861 and 0.5108 for horizontal and vertical canopies, respectively). The vertical trellis seemed to have a windbreak effect that tended to reduce E_s compared to the slanting trellis. Therefore, clay content and trellis orientation effects on β need to be considered.

Keywords: βvalue, clay content, lysimeter, saturated hydraulic conductivity, trellis system