Agriculture Reference
In-Depth Information
no shade (80% to 100% of full sunlight), coffee must be fertilized more heavily
to reach a greater yield potential. Muschler (1997) proposed that only in
certain optimum growing conditions is the complete absence of shade advan-
tageous for coffee production. Otherwise, some level of shade, depending on
growing conditions,fertilizer inputs,and coffee varieties,should be included.
The use of shade trees in coffee orchards maintains or improves soil condi-
tions by reducing soil temperatures and erosion, adding organic matter, recy-
cling subsoil nutrients, and in the case of legumes, adding nitrogen. Shade
trees also create less favorable conditions for weed growth, thereby reducing
the need for hand-weeding or herbicides. Nestel & Altieri (1992) investigated
weed biomass production and species composition in Mexican coffee orchards
that differed in shade level and species mix.Measurements were made in plots
of coffee grown in pure stand (unshaded), in mixture with trees of the genus
Inga
(monogeneric shade), and in mixture with trees in the genera
Inga
,
Citrus
,
and
Musa
(polygeneric shade).Coffee trees were 8-12 years old and shade trees
were 8-15 years old. Plots were cleared of weeds by hand at the start of both
the wet and dry seasons, but no other weed control measures were used.
Weed biomass increased at a much lower rate in the two shade treatments
than in the unshaded treatment. In the wet season, the unshaded treatment
accumulated
2000 kg ha
1
of weed biomass, whereas weed biomass in the
shaded treatments reached only 800-1000 kg ha
1
(Figure 7.10). In the dry
season, weed biomass in the unshaded treatment rose to
1500 kg ha
1
, but
reached only 200 kg ha
1
in monogeneric shade and 400 kg ha
1
in polygen-
eric shade (Figure 7.10). In shaded treatments, weeds in the Commelinaceae
(
Tripogandra serrulata
and
Commelina erecta
) were most abundant, whereas
without shade, weeds in the Asteraceae (
Galinsoga quadriradiata
,
Smallanthus
maculatus
,
Bidens alba
, and
Melampodium microcephalum
) were most abundant.
Nestel & Altieri (1992) noted that local growers considered weeds in the
Asteraceae to be more difficult to control and more damaging to coffee than
weeds in the Commelinaceae. The investigators proposed that differences
among shade treatments in weed biomass and community composition could
be related to solar radiation levels and allelopathic interactions.Water extracts
from
Inga
and
Musa
leaves and roots have been reported to inhibit germina-
tion and root elongation of weeds in the Asteraceae and Gramineae, but to
have less effect on those in the Commelinaceae (Anaya
et al
., 1982).
The natural growth of most overstory tree species often results in greater
than optimum shade levels in numerous patches within a multistory orchard.
The regulation of shade levels through pruning as frequently as twice annu-
ally can improve the light environment for coffee production and generate
additional leaf litter for localized weed control and ground cover. As was
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