Agriculture Reference
In-Depth Information
agroforestry systems, i.e., farming systems where trees and crops are grown simul-
taneously on the same plots, confirm this range. In a study on intercropping of
Faidherbia
with beans and maize in the Morogoro region of Tanzania, Okorio and
Maghembe (1994) reported biomass production in trees ranging between 2.1 and 4.7
Mg ha
−1
year
−1
on average during 6 years, depending on tree spacing. Intercropping
of
Gliricidia
with maize during 10 years in Malawi produced a total of 20.5 Mg ha
−1
of tree prunings for incorporation into the soil, corresponding to 2.9 Mg ha
−1
year
−1
(Makumba et al. 2007).
Results from a 7-year trial in the same study with slightly different tree man-
agement showed substantially lower biomass accumulation in tree prunings of only
around 1.1 Mg ha
−1
year
−1
(Makumba et al. 2007). Considering that destructive sam-
pling of trees at the end of the trial also revealed 17 Mg ha
−1
in tree stumps and struc-
tural roots, the total biomass accumulation per year should nevertheless have been
around 2.7 Mg ha
−1
year
−1
, on average, so that this trial also falls within the range
estimated by Montagnini and Nair (2004).
Much lower biomass accumulation rates have been reported from agroforestry
practices in western Kenya (Henry et al. 2009). In this study, aboveground biomass
was measured on 35 farms across two administrative districts. Assuming biomass
levels on all farms could be raised to reach the third quartile of the distribution of
measured biomass for the respective district, aboveground biomass accumulation
potentials were estimated for different land use types. With the exception of wind-
rows and rotational woodlots, all agroforestry systems evaluated had biomass buildup
potentials below the range specified by Montagnini and Nair (2004). Converting
figures from Henry et al. (2009) from C stocks to biomass stocks (at 45%-50% C in
biomass), individual trees in home gardens were expected to raise biomass levels by
0.3 and 0.6 Mg ha
−1
year
−1
. Individual trees in food crops had biomass accumulation
potential between 0.2 and 0.3 Mg ha
−1
year
−1
, individual trees in cash crops between
0.1 and 0.4 Mg ha
−1
year
−1
, and individual trees in pastures around 0.1 Mg ha
−1
year
−1
.
Windrows had higher potential at 2.9-3.5 Mg ha
−1
year
−1
, and biomass buildup in
rotational woodlots was substantial at 2.3-12.2 Mg ha
−1
year
−1
. Two scenarios of
intensifying hedgerow biomass had potential of accumulating between 0.2 and
0.5 Mg ha
−1
year
−1
of biomass.
11.3.1.2 Improved Fallows
Several studies have estimated biomass buildup in improved fallow systems. Albrecht
and Kandji (2003) tabulated data from several studies using a range of tree species,
in which aboveground biomass stocks ranged from 7.0 to 21.0 Mg ha
−1
year
−1
after
12 months, from 19.8 to 31.0 Mg ha
−1
year
−1
after 18 months, and from 27.0 to 43.4 Mg
ha
−1
year
−1
after 22 months. These values appear on the high side of what is realistic,
and are in contrast to modeling results by Walker et al. (2008) for biomass buildup in
the IMPALA project, in which some of the figures in the table were generated. They
estimated biomass buildup of only 10-32 Mg ha
−1
after 10 years, corresponding to an
average accumulation rate of only 1.0-3.2 Mg ha
−1
year
−1
(Walker et al. 2008).
Kaonga and Coleman (2008) measured aboveground C inputs in coppiced fallows
in Zambia. These were in the range of 2.6-3.2 Mg C ha
−1
year
−1
for multiple species
