Agroforestry for sustainable bioenergy and improved soil fertility in two agro-ecological zones, Rwanda
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Date
2024
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine University of Agriculture
Abstract
In Rwanda, the demand for food and energy is high and rising due
to population growth. Furthermore, in rural households, the primary
energy
supply
is
from
fuelwood
combusted
in
inefficient
cookstoves, resulting in fuel wastage and health issues associated
with smoke in the kitchen. Biochar produced in cooking stoves can
contribute to negative carbon emissions through sequestration of
biomass Carbon while also providing other benefits for sustainable
development, including provision of clean renewable energy and
increased yields in tropical agriculture. In addition, B has low
nutrient
content
and
is
recalcitrant
to
biodegradation;
supplementing B with a fast-releasing nutrient source may
contribute to improving soil fertility and physical conditions and lead
to increased crop productivity. The reported research aimed to
assess the impact of introducing Biochar-producing cooking stoves
on household energy access and vegetable production, both on
smallholder farms and experimental stations, in two agro-ecological
zones (AEZs) of Rwanda. Participatory research on B production
and use was conducted with 60 smallholder farmers selected
purposively to evaluate the potential of Biochar – producing
cooking stoves to address the interconnected challenges of
household energy access and low vegetable productivity in
Rwanda. The study compared two top-up lift draft (TLUD) gasifier
types (Gastov and Karundura) with a three-stone fire (TSF)
cookstove, using a standardized cooking test (SCT) and a
household survey. Key indicators included cooking time, firewood
usage and Biochar yield while the survey collected informationii
about fuel availability, frequency of use, gasifier design, benefits
and challenges. In addition, a three-season field study was done in
two AEZs to assess the Biochar effects on vegetable yields after
application to soil, where Biochar from gasifier stoves was applied
in furrows (2-3 cm deep) in the gardens of French beans
(Phaseolus vulgaris) at a rate of 3 tons per hectare (t/ha) using
randomized paired design. Yield and the soil’s physical and
chemical properties were analyzed. Concurrently, another, three-
season field study (on station trials) was conducted in two AEZs to
assess the synergistic effect of five types of Biochar (from S.
sesban, G. sepium, A. angustissima, Eucalyptus, and Grevillea sp.)
alone or mixed with livestock manure (LM) and applied at 1 and 3 t/
ha using French bean as a test crop. The key indicators were
French bean yields, and soil chemical properties of soils. The study
utilized descriptive statistics, one-way analysis of variance
(ANOVA) using a generalized model in R, linear fixed effect model
and the difference between means was examined using Tukey’s
test at p<0.05. The study revealed that the TSF stove cooked a
standardized meal faster than the gasifier stove did but the later
reduced fuelwood consumption by 25-50% and produced biochar.
The household survey responses revealed low firewood availability,
but with the ability of firewood, savings when using gasifier stove.
Gasifier stoves provided benefits through temperature control,
reduced need for constant supervision, Biochar production, and
reduced time needed for fuelwood collection, more hygienic and
attractive appearance cooking. Most household cooks reported that
the gasifier stoves produced less smoke and were safer for
children and women’s health. The findings from on-farm trialsiii
showed a consistently positive response in French bean yield
following a one-time application of B in both sites. The B-treated
plots were significantly (P<0.05) higher in pH, plant available
nutrients (available Phosphorus (P), total Nitrogen (TN) and
exchangeable bases), and soil nutrient retention capacity (high
cation exchange capacity (CEC)). Soil porosity, plant available
water (PAW), were significantly increased by B application while
reducing soil bulk density (BD). The B produced by the TLUD
gasifiers was perceived as positive as it combines B production
and bioenergy, reduces off-farm biomass gathering, improves
energy security and produces sufficient B to improve soil
productivity in home gardens. For the on-station trials, the seasonal
increase in yield has been recorded in combined plots with the high
yield found in B-LM, each at the level of 3 t/ha, compared to the
sole application of LM or B and the control treatment. The main
factors for the increase of the French bean yield in the study areas
are improved soil properties, including high pH; high nutrients
content (Avail P, TN), soil OC and soil CEC. The application of B,
either alone or in combination with LM, positively increased soil
nutrients and French bean yield. The improvement became better
as the B rate increased and when mixed with LM than sole
application of B or LM. Increased vegetable yield enables
enhanced nutrition and/or market opportunities and the adoption of
the TLUD stoves may contribute to energy sustainability through
the reduction of fuel use. The study recommends considering the
combination of B with LM as an effective land rehabilitation strategy
to improve soil fertility and increase vegetable yield in Rwanda.
This technology of using B and LM is a low-cost technology foriv
managing acidic sandy soils of Rwanda. The technology offers
significant contributions in terms of improving soil fertility,
increasing
bioenergy
output,
mitigating
climate
change
by
sequestering atmospheric carbon in the soil and reducing
greenhouse gas emissions associated with traditional cooking
methods, particularly for women and children, thus improving the
overall
well-being
and
socio-economic
stability
of
rural
communities.
Description
Dissertation
Keywords
TLUD, three-stone fire cookstove, fuel saving, cooking time, Biochar, soil properties, French bean yield, smallholder farmer, Rwanda.