Agriculture Reference
In-Depth Information
pigeonpea sole crops. This was due to both higher yield and lower variance of
yield.
Resource use and weed suppression
Weed suppression by intercrops is often, but not always, better than
that obtained from sole crops (Liebman & Dyck, 1993). Greater land use effi-
ciency, yield stability, and weed suppression of intercropping relative to sole
cropping all appear to derive from complementary patterns of resource use
and facilitative interactions between crop species.
Complementary use of resources occurs when the component species of an
intercrop use qualitatively different resources, or use the same resources at
different places or different times. Complementarity can exist between crops
that differ in nitrogen sources (e.g.,in mixtures of legumes and non-legumes),
photosynthetic responses to varying light intensities (e.g., in mixtures of C
3
and C
4
species),rooting depth,peak periods of leaf area display and root activ-
ity, and other physiological, spatial, and temporal aspects of resource use
(Snaydon & Harris, 1981; Ofori & Stern, 1987; Willey, 1990). In ecological
terms, resource complementarity minimizes niche overlap and competition
between crop species, and permits crop mixtures to capture a greater range
and quantity of resources than can sole crops (Vandermeer, 1989).
Facilitative interactions occur when one crop species directly or indirectly
aids the growth of another (Vandermeer, 1989). Taller crops can improve the
growth and yield of shorter crops by reducing wind speed and improving
water use efficiency (Radke & Hagstrom, 1976). Erect crops can improve the
performance of climbing crops by providing physical support (Budelman
1990
a
, 1990
b
). Growth and yield of non-legume crops may be increased by N
transfer from roots of associated legume species (Agboola & Fayemi, 1972;
Eaglesham
et al
., 1981). Various crop species may also reduce the amount of
insect and disease damage suffered by associated crops by (i) disrupting the
ability of pests to locate,move to,feed upon,or infect host plants,or by (ii) pro-
viding favorable conditions for the proliferation and effective action of
natural enemies of pests (Vandermeer, 1989; Trenbath, 1993; Altieri, 1994;
Liebman, 1995).
Because complementary patterns of resource use and facilitative interac-
tions between intercrop components can lead to greater capture of light,
water, and nutrients, intercrops can be more effective than sole crops in
preempting resources used by weeds and suppressing weed growth. Linkages
between resource use and weed suppression can be seen in a study conducted
by Abraham & Singh (1984), who planted sorghum alone and in mixture with
different legume species (fodder cowpea, grain cowpea, soybean, mungbean,
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