Effect of plant population density and shading on the productivity of beans (Phaseolus vulgaris L.) and beets (Beta vulgaris L.) under intercropping
Abstract
Intercropping is a common practice throughout the world, but sole cropping systems
predominate where advanced production technologies are widely available. The associated
species in an intercropping system tend to interfere, mainly through either competition for
mutually required resources or release of allelopathic chemicals to the microenvironment. This
interference intensifies as the density of each component species increases. An experiment was
performed to determine the effect of species population densities and shade on yield and yield
components of beans (Phaseolus vulgaris L.) and beets (Beta vulgaris L.). Plants of each
species were sown at four densities, in a split-plot randomized complete block design under two
light intensity levels (full sun and partial shade). Analysis of variance, yield-density regressions,
land equivalent ratios and light absorption-density regressions were used to quantify and
interpret the treatment effects.
The analysis of variance indicated that yield per plant was significantly reduced by
increasing density of each species, and 'by decreasing light intensity for most of the growth
measures. Inverse regression parameter values for most of the yield variables revealed that beet
was a stronger competitor than bean. Beet was also found to be more competitive than bean
under full sun, but not under shade.
Bean dry-matter allocation to leaves, stems and pods was also observed to decrease with
increasing bean and beet population densities. An exception to this was the allocation to leaves,
which was not significantly affected by bean density. Beet density had no significant effect on
its dry-matter allocation, but bean density caused significant reduction in beet dry-matter
allocation to petioles and storage root.
Land equivalent ratios (LER) were approximately equal to 1 indicating neither
overyielding nor underyielding. The contribution of bean to LER was always lower than that of
beet for all the variables.
Light interception was found to increase with species population densities and time.
Bean was superior to beet in terms of light interception, which may account for the competitive
improvement of bean observed under shade.
Citation
Degree of Master of SciencePublisher
University of Nairobi Department of Plant Science
Description
A thesis submitted in partial fulfillment for the Degree
of
Master of Science