ISHS Acta Horticulturae 537: III International Symposium on Irrigation of Horticultural Crops
CROP COEFFICIENTS FOR MATURE PEACH TREES ARE WELL CORRELATED WITH MIDDAY CANOPY LIGHT INTERCEPTION |
| Authors: | R.S. Johnson, J. Ayars, T. Trout, R. Mead, C. Phene |
| Keywords: | Peach, Prunus persica, Evapotranspiration, ET, Light interception, Lysimeter, Crop coefficient. |
| DOI: | 10.17660/ActaHortic.2000.537.53 |
| Abstract:
Two ‘O’Henry’ peach trees were planted in a 2x4x2 m weighing lysimeter in the spring of 1988. An additional 1186 trees were planted in the 1.1 ha field surrounding the lysimeter. Row and tree spacing were 4.9 and 1.8 m respectively, and trees were trained to a “V” shape perpendicular to the row. The irrigation system in the field consisted of one 20 L/hr microsprinkler per tree. Within the lysimeter, a circle of ten 2 L/hr drip emitters per tree simulated this same pattern of water distribution. Irrigation was automatically called for when 5.4 mm of ET was lost from the lysimeter trees, which resulted in approximately daily irrigations during the summer. Daily peach ET values (ETc) were recorded during the growing seasons of 1990 to 1994 when the trees were mature. Reference crop values (ETo) were calculated from a nearby weather station using a modified Penman equation. Crop coefficients (Kc) were calculated as the ratio of these two (ETc/ETo). Kc values generally started at about 0.2 early in the season and reached as high as 1.1 to 1.2 by August. The increase in Kc values over the growing season and year-to-year variability was largely accounted for by midday tree canopy light interception. Weather parameters such as vapor pressure deficit, wind speed, temperatures and solar radiation accounted for very little additional variability. Therefore, light interception seems to be the main variable needed to explain changes in Kc due to tree size and leaf area development, and may even apply to young trees and different tree and vine species. | |
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