Agriculture Reference
In-Depth Information
6
Enhancing the competitive ability of crops
Introduction
Many cultural practices, including crop density, arrangement, plant-
ing date and choice of cultivar affect the crop's ability to compete with weeds.
However, most recommendations for the planting of crops are based on the
assumption that weeds are absent. This is a result of the scientific and eco-
nomic context in which recommendations are developed. Variety trials, fertil-
ity rate trials, and many other agronomic experiments are usually run in
weed-free conditions to avoid the confounding effect of weed competition.
For the agronomist or horticultural scientist,keeping a particular experiment
free of weeds is a practical possibility.Given the high spatial and temporal var-
iability in density and composition of weed communities, a weed-free trial
may also be the easiest way to generate results that are applicable over a wide
area. In addition, weeds generally decrease yield regardless of other parame-
ters. Consequently, weeds are usually excluded from experiments unless they
are specifically the object of investigation.However,weed-free fields are rarely
practical on the farm, and as explained in the following sections, the presence
of weeds generally changes the optimal choices for cultural practices relative
to those developed in weed-free conditions.
The central thesis of this chapter is that the density, arrangement, cultivar, and
planting date of the crop that maximize the rate at which the crop occupies space early in
the growing season usually minimize competitive pressure of weeds on the crop . These
cultural factors also have other effects on the competitive balance between
weeds and crops. For example, allelopathic cultivars sometimes reduce weed
biomass. However, the physical occupation of three-dimensional space by the
crop, and the preemption of resources that this allows, is central to the opera-
tion of cultural weed control strategies discussed here and in the following
chapter.
269
Search WWH ::




Custom Search