Crop diversification for weed management - Ecological Management of Agricultural Weeds - page 349

Figure 7.8 Weed biomass present in a barley sole crop and a barley/red clover
intercrop at the time ofbarley harvest (summer,year 1) and in stubble at
subsequent sampling dates (fall,year 1; spring,year 2),in an experiment
conducted from 1988 to 1993 in Maine,USA.(M.Liebman,unpublished data.)
(Kendall & Stringer, 1985) and is thus well adapted to growing under barley.
After the barley is harvested, the clover rapidly develops a dense canopy that
shades weeds.
Delayed seeding of minor crops into established main crops offers a more
predictably successful approach for reducing or eliminating competition
against main crops while gaining some improvement in weed control.
Because this type of intercropping is generally conducted after a final weeding
operation,any weed control advantage it may provide derives from the combi-
nation of direct control measures with competition from the smother crop.An
example of how such a system may work is shown in a study by Sengupta,
Bhattacharyya & Chatterjee (1985). They compared weed growth (mostly
grasses and sedges) and crop yields in an unweeded rice sole crop, an
unweeded rice/blackgram intercrop with both crops sown simultaneously,
and a rice/blackgram relay intercrop in which rice was sown first and black-
gram was added 21 days later after one hand-weeding. Weed density and