ISHS Acta Horticulturae 175: Symposium on Physiology of Productivity of Subtropical and Tropical Tree Fruits
MEASUREMENT OF SOLAR RADIATION INTERCEPTION BY TREE CROPS |
| Author: | J.W. Daniells |
| Abstract:
Growth and economic yield have been expressed (1) as the product of three simple indices :- radiation interception, efficiency of conversion of solar energy to plant material and harvest index. In the absence of environmental constraints radiation interception is the main determinant of biological yield and, together with harvest index, the main determinant of economic yield. Information on radiation interception thus gives a clearer understanding of how yield differences develop. Despite its importance, radiation interception is seldom measured in tree crops (2). This is for a number of reasons, not the least of them being difficulties in sampling large areas properly. Techniques that have been used to measure interception have included light sensing cells with and without integration, photochemical methods and fisheye photography (3). A method has been developed (G. Kerven pers. comm.) which is used to measure radiation transmission to pastures beneath coconut canopies in the Solomon Islands. It has application to the measurement of radiation interception in tall tree crops where there is sufficient walking access beneath the canopy. The method uses two Li-Cor Integrating Quantum Meters (LI-188B) and two Quantum Sensors (LI-190SB) which measure photosynthetically active radiation (PAR). One unit is placed in full sunlight outside the canopy (Plate 1) and the second is used to make a hand-held transect through the required measurement area (Plate 2). The two units are independent of one another. After starting them at the same time they will integrate over periods of 1; 10; 100 or 1000 seconds as required. Percent of PAR intercepted can then be calculated. Where walking access beneath the canopy is not possible an alternative approach would be to pull the sensor through the crop on a miniature railway. The cost of the measurement equipment is A$5000 + and would be a valuable resource for any tree crops research establishment. | |
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