ISHS Acta Horticulturae 278: Symposium on Scheduling of Irrigation for Vegetable Crops under Field Condition
A PORTABLE CHAMBER FOR EVAPOTRANSPIRATION MEASUREMENTS AND IRRIGATION SCHEDULING |
| Author: | D.C. Reicosky |
| Abstract:
Improved water management to increase water use efficiency requires development of research tools that provide accurate measurements of evapotranspiration (ET). The objective of this work is to describe a portable chamber for measuring ET in the field and to show its utility for developing and evaluating irrigation scheduling criteria. The chamber is placed over the canopy for 60 seconds and the rate of water vapor increase measured with an infrared gas analyzer. Midday leaf water potential and canopy air temperature collected on corn and soybean during the 1988 growing season were related to ET. Days selected for detailed analysis were during maximum leaf area index around anthesis, cloud-free, and at least two days from rainfall or irrigation to minimize soil evaporation and respiration contributions to the net gas exchange. The chamber was accurate over a wide range of evaporation rates from a low of 0.04 to a high of 1.1 mm hr-1. Results from this field study showed ET related to leaf water potential, with both decreasing as soil water stress became severe. Air temperature within the canopy of stressed corn and soybean increased progressively during periods of high evaporative demand as soil water deficit increased. Within-canopy air temperatures can increase as much as 4 to 6°C while ET decreased to about 20% of ET on irrigated plots. High In-canopy air temperatures were associated with leaf water potentials that ranged from -1.6 to -3.0 MPa for both corn and soybean. The relationship between ET and leaf water potential and in-canopy air temperature during severe soil water deficits suggest ET measured by the chamber can be used to develop and evaluate simple irrigation scheduling techniques. | |
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