Energy exchange within the crop canopy of townsville stylo, Stylosanthes humilis H.B.K.
✍ Scribed by J.H. Goncz; C.W. Rose
- Publisher
- Elsevier Science
- Year
- 1971
- Weight
- 817 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0002-1571
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✦ Synopsis
For 22 days in March and April, 1967, an intensive micrometeorological study was conducted in a sown pasture of Townsville stylo (Stylosanthes humilis H.B.K.). Other papers have treated the morphology and climate of the crop, and energy transport between crop and atmosphere.
The method of energy balance analysis applied successfully to the crop data might be expected to be applicable also to studying transport phenomena within the canopy. It appears, however, that the assumption of vertical energy transport can not be applied to this canopy without reservation.
There existed periods in the first day of the study during which a one-dimensional theory of the canopy would not explain the field data, particularly the vapour pressure profiles. On following days the apparent anomalies in vapour pressure profiles persisted for longer periods, eventually encompassing the whole day.
The anomaly in vapour pressure profiles was the appearance of a layer mid-way in the canopy in which the specific vapour pressure was less than in the layers above and below, which, if interpreted in terms of one-dimensional model would indicate a sink of water vapour. It is hypothesized that the explanation for this anomaly is associated with preferential ventilation of the inner layer of the canopy by air from above the canopy, i.e., a "tunneling effect".
Because of the trend towards more extensive data acquisition, an objective of present research is to develop methods of machine data processing to replace traditional methods of micrometeorological analysis, which at present take place in two steps: (1) interpolate (frequently by hand) the field data to obtain continuous profiles; and (2) differentiate the profiles to calculate energy exchange. A mathematical model of the canopy was developed in which both of these steps are performed simultaneously and certain physical relations deriving from the assumption of vertical energy transport are used to guide the computational logic. The model stresses continuity in latent and sensible heat flux and turbulent diffusivity at the interface between crop surface and atmosphere.