Determining input values for a simple parametric model to estimate evaporation from vineyard soils with special reference to clay content and trellis system
Estimating soil evaporation (Es) is an important part of modelling vineyard evapotranspiration for irrigation purposes. Furthermore, quantification of possible soil texture and trellis effects is essential. Daily Es from six topsoils packed into lysimeters was measured under grapevines on slanting and vertical trellises, respectively. Following irrigation, cumulative soil evaporation (∑Es) from the bare, untilled soils over 14-day drying cycles was plotted against cumulative reference evapotranspiration (∑ETo) to determine Estransition from the constant rate stage (Stage 1) to the falling-rate stage (Stage 2). During Stages 1 and 2, rate of Es is determined by atmospheric conditions and soil properties, respectively. Slopes of ∑Es vs square root of ∑ETo plots in Stage 2 provided the input constant (β value) for each soil. In Stage 1, ∑Es was almost equal to ∑ETo but the ratio varied as grapevine canopies developed. The β values varied between 2.15 ±0.09 mm0.5 and 4.68 ± 0.14 mm0.5 . 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 Es 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