last final thesis of umer

Photo synthetically active radiation (PAR), which is utilized by green leaves, conservatively makes up
about 50% of global short wave radiation (Szeicz, 1974). Compared to high variability that occurs in
the supply of water and nutrients to the plant, solar radiation is more reliable and used sufficiently by
intercrops as they form a complete cover to allow full interception. Solar radiation cannot be stored for
later use, it must be intercepted and utilized instantaneously to energize the photosynthesis process.
Therefore, neighboring plants compete for solar radiation by direct interception (Keating & Carberry,
1993).
Studies on crop mixtures e.g. intercropping and crop/weed interactions, have concentrated on the
competition for resources between species and the emphasis in the case of competition for light
has been placed on the ability of one species to compete with and shade another (Caldwell,
1987).Differences between species, plant density, developmental pattern, plant height, canopy
architecture, foliage overlap, photosynthetic rate and in the assimilate reserves, result in great
structural complexity in mixed-species canopies.
Leaf area index (LAI), is the amount of green leaf area per unit of ground area, which is a parameter
commonly used to describe the probability of light interception in relation to crop canopies
(Keating & Carberry, 1993). Great diversity in intercrop canopies is possible, resulting from the
various combinations in space and time of planting date and spatial distribution, leaf size, shape
and orientation and plant height.
The canopy characteristics of component crops are not constant, but may change due to the
presence of other crop species (Caldwell, 1987). Crop yield is closely related to assimilate
production during the yield development period of crop growth, although it is difficult to relate
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