Effect of Increasing Foliage and Soil Reflectivity on the Solar Radiation Balance of Wide-row Grain Sorghum1
- M. Fuchs,
- G. Stanhill and
- S. Moreshet2
Excessive radiant heat load limits the growh of plants in dryland farming during the rainless summer. The use of reflectants to control the radiation balance in field conditions is examined here.
Modifications of the solar radiation balance in a wide-row sorghum [Sorghum bicolor (L.) Moench ‘726’] crop grown on a dark brown grumusol (Chromoxererts) were obtained by spraying a white kaolin suspension on 1,000 m2 field plots. Treatments consisted of separate applications of the kaolin on the foliage and on the soil surface, and combined applications on both the foliage and the soil.
Radiation transfer equations were used to quantify the effect of the various treatments on the solar radiation absorption of the foliage, and of the soil. These equations account for the presence of direct and diffuse components in the downward solar flux and make specific reference to a simplified definition of the radiation scattering properties of the foliage and the soil. Measurements of the diurnal variation of the solar radiation reflection above each experimental plot and fisheye determinations of the foliage distribution validated the simplifying assumptions used in deriving the transfer equations. With some additional assumptions the equations are extended to predict absorption by the foliage and the soil from daily totals of the global radiation.
The reflectivity of the foliage increased by 24% immediately after spraying kaolin on the canopy. A 17%, increase persisted 5 weeks later. The corresponding seasonal net solar absorption was reduced by 6%. The soil treatment doubled the solar reflectivity of the soil, causing an 18% decrease of the solar absorption by the soil. The increased reflected solar flux from the soil surface was partly intercepted by the foliage, and produced a 9% increase of absorption by the foliage. The application of kaolin to both the foliage and the soil resulted in very little change in the absorption by the canopy, the whitening of the foliage being offset by the addition of the radiation reflected by the soil, but was mast effective in increasing the solar reflection from the field. Larger reductions of the canopy solar radiation balance can he expected by improving the dispersion of the kaolin coating on the entire foliage.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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