Crop diversification for weed management - Ecological Management of Agricultural Weeds - page 343

Table 7.1. Above-ground biomass of weeds (g m 2 ) present in fava bean and wheat sole
crops and intercrops sown at different densities in an experiment conducted in Berkshire,
UK.Recommended densities for fava bean and wheat sole crops were 25 and 250 plants
m 2 , respectively

Wheat density a

Fava bean density a 0 25 50 75 100

0 — 302 146 97 124

25 398 168 148 96 93

50 346 162 133 80 100

75 284 138 151 75 36

100 169 117 72 83 62

Notes:
a Percentage ofrecommended sole crop density.
Source: Adapted from Bulson,Snaydon & Stopes (1997).

Table 7.2. Land equivalent ratios (LER) of fava bean/wheat intercrops sown at different
densities, based on seed yields of 3.7 Mg ha 1 for both fava bean and wheat sole crops
grown at their respective recommended densities (25 and 250 plants m 2 )

Wheat density a

Fava bean density a 25 50 75 100

25 0.76 1.06 1.02 1.27

50 0.86 1.08 1.05 1.25

75 0.94 1.16 1.29 1.27

100 0.97 1.15 1.24 1.16

Notes:
a Percentage ofrecommended sole-crop density.
Source: Adapted from Bulson,Snaydon & Stopes (1997).

normal sole crop density (i.e.,a 150% mixture) provided the highest LERvalue
(1.29) obtained in the experiment. Similarly, intercrop yield advantages over
sole crops rose with increasing density in mixtures of sorghum with pigeon-
pea (Shetty & Rao, 1981) and barley with pea (Mohler & Liebman, 1987).
The preceding discussion of how intercropping affects weeds and crop
yields indicates that increases in crop diversity through intercropping may or
may not provide weed control advantages over sole cropping. However,
increases in crop density consistently reduce weed biomass in intercrops as
they do in sole crops (see Chapter 6), and intercropping often allows use of a