Agriculture Reference
In-Depth Information
biomass were lowest and rice yield and monetary return were highest in the
relay intercropping system.
Weed control can be improved in maize production systems by planting a
smother crop at the last cultivation, about one month after sowing maize.
Samson,Foulds & Patriquin (1990) found that late-season weed biomass could
be reduced up to 63% by interseeding annual or perennial ryegrass into maize.
Although relay intercropping with ryegrass had no effect on maize yield, it
probably did reduce the number of weed propagules that would infest future
crops. Samson, Foulds & Patriquin (1990) recommended against sowing rye-
grass into established maize crops with grain yield potentials of
9 Mg ha 1 ,
since such vigorous crops would be overly competitive for light, water, and
nutrients.
More extensive use of smother crops would be fostered by the development
of short-lived, short-statured genotypes that suppress weed establishment
during the early part of the growing season, but senesce before competing
with main crops (De Haan, Scheaffer & Barnes, 1997; De Haan et al ., 1997).
Efforts to develop such genotypes will require the active participation of plant
breeders.They will also require a better understanding of the ecophysiologies
of minor crops, main crops, and weeds, and the characteristics of competitive
interactions among them.
Changes in weed community composition due to
intercropping
In contrast to crop rotation, which alters weed communities through
the effects of different crops sequenced over multiple seasons, intercropping
combines the effects of different crops within a single season. Will farmers
encounter different species of weeds or different proportions of weed species
in intercropping systems compared with sole cropping systems? If so, how
might these differences be predicted? Two impacts of intercropping on weed
community organization appear particularly important.
First,the dominant weed species found in intercrops may closely reflect the
identities and proportions of the different component crops, each of which
may have distinct associated weed communities. Shetty & Rao (1981)
observed, for example, that the weed community of sole-cropped peanut was
dominated by Digitaria , Cyperus , and Celosia spp., which produced about 3%,
40%, and 50%, respectively, of the total weed biomass. In contrast, the weed
community of sole-cropped millet was a mixture of many species, with
Digitaria , Cyperus , and Celosia spp. constituting about 25%, 15%, and 5%,
respectively, of total weed biomass. Celosia and Digitaria grew taller than
peanut, whereas Cyperus grew beneath the peanut canopy and was shaded by
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