Components of the energy and heat balances were examined
in two maize hybrids grown at three different plant densities
(40, 70 and 100 thousand plants per hectare). One of the
hybrids was drought tolerant, while the other was bred for
cultivation under irrigated conditions. An increase in plant
density influenced not only the size of the leaf area, but also
the distribution of the leaves at various plant heights. The
extinction coefficient, which provides a quantification of
radiation penetration, was higher in the irrigated treatments.
By contrast to the other two treatments, the plant
canopy in the thinly sown stands remained open throughout
the vegetation period, and thus behaved quite differently to
the closed stands, making it impossible to compare them.
Smaller albedo values were recorded for the hybrid bred for
irrigation and in thinly sown stands. The low plant density
allowed more energy to reach the soil, from which it was
reflected, making a considerable contribution to the final
temperature in the stand. The latent heat, in keeping with
the quantity of water transpired, was the greatest in the
densely sown stands. There was little difference between the
latent heat values of the normal and dense stands in either
hybrid, indicating that they both had a similar sensitivity to
increased stand density. If sufficient water is available it
would appear that the stand density could be increased even
for the drought-tolerant hybrid
