Agriculture Reference
In-Depth Information
The total uptake of nutrients in the age series of alder-cardamom systems varied
from 90 to 239 kg ha
−1
year
−1
for nitrogen and from 4 to 10 kg ha
−1
year
−1
for
phosphorus (Sharma et al. 2002b). Values were lower for nitrogen and higher
for phosphorus when compared to the monoculture of the same species of alder in
the region (Sharma 1993). Rawat and Singh (1988) estimated the nutrient uptake in a
Himalayan oak forest to be 230 kg ha
−1
year
−1
for nitrogen and 13 kg ha
−1
year
−1
for
phosphorus. These comparisons show that pure alder forests have higher nitrogen
and lower phosphorus uptake, but that in the mixed stands, cardamom nitrogen
uptake decreases while phosphorus uptake increases. The low phosphorus uptake
in pure alder stands was attributed to a negative effect of alder on the phosphorus
economy, mostly by increasing soil acidity (Sharma 1993). This caused phosphate
to react with iron and aluminium to form less soluble phosphate compounds
(Brozek 1990; Sharma et al. 1997). Furthermore, a heavy accumulation of organic
matter in soils of pure alder stands could have shifted phosphorus from a plant-
available pool to an organically bound pool (Sharma 1993). The combination of
alder with cardamom is a system in which nitrogen and phosphorus uptakes are
balanced, unlike in either pure stands of an N
2
-fixing species such as alder, or a
non-N
2
-fixing species.
The nitrogen and phosphorus cycling in the cardamom agroforestry system
appeared to be very malleable (flexible) under the influence of the N
2
-fixing alder.
Binkley et al. (1992) have also reported that alder results in a generally higher
uptake and return of all nutrients, and a greater magnitude of malleability of nutri-
ent cycles are consistent with the findings from the alder-cardamom system. We
have observed that the agroforestry system was more productive when alder was
integrated into the system, resulting in faster rates of nutrient cycling. The poor
nutrient conservation, low nutrient use efficiency and the malleability of nutrient
cycling in alder systems make the alder tree an excellent associate that promotes
higher availability and faster cycling of nutrients.
18.3.4
Biodiversity Values and Conservation
Biodiversity is an important indicator for sustainability. Biologically diversified sys-
tems have a greater adaptive capacity for resilience and show greater sustenance.
The cardamom is native from Sikkim in the Eastern Himalayas, and the occurrence
of five species of wild cardamom (
Amomum linguiforme
,
A. kingii
,
A. aromaticum
,
A. carynostachym
,
and A. dealbatum
) shows high genetic reserves.
Amomum subu-
latum
is a cultivated species of cardamom and its cultivation system supports a
highly diverse range of shade trees (Sharma and Sharma 1997). Our study supported
this since up to 23 species were found. The Shannon and Weaver diversity index of
trees in a cardamom dominated system was 4.1. This indicates that there is a fairly
good composition of trees providing fodder and firewood to farming families. Most
of the cardamom agroforestry have alder as shade trees. However, small patches are
maintained with mixed trees so as to meet the fodder requirements of households.
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