1. Comparative Assessment of Biomass and Soil Carbon Stocks in Multi-strata Agro-forestry Systems and Khat (Catha Edulis) Farming, Northern Ethiopia
Desalegn Getnet, Mesele Negash, Abeje Eshete
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Introduction
Methods
Results
Conclusions and Recommendation
The study was conducted in Raya Azebo district, Northern Ethiopia.
Reconnaissance survey carried on selected woreds and Werabay-Lati and beyaru-Kalena kebeles were purposively selected.
AFS in study site were grouped: as CAF, FAF and KF
A total of 60 farms (10 farmers x 3 systems x 2 sites) were randomly selected from the total house holed head.
All woody species with ≥ 2.5 cm DBH and total height ≥ 1.5 m in each plot were measured across the three studied systems.
For coffee and khat individual plants, stump diameters at 40 cm (d40) and 10 cm (d10) were recorded
Litter biomass was collected from 3 sub plots (1 m x 1 m) in each bigger plot.
A total of 120 composited samples were collected (2 site replications x 2 soil depths x 3 systems x 10 farms) for SOC, TN, pH and texture analysis.
Above and belowground biomass of fruit bearing trees and coffee plants were estimated using already developed allometric equations, while for khat plant a new allometric equation was developed for estimation of above ground biomass.
SOC, Mg ha-1 = [(soil bulk density, (g/ cm3) x soil depth (cm) x C %)] *100 (Pearson et al., 2007).
Globally agroforestry systems (AFS) estimated to be practiced on M ha and to sequester from 30 to 322 C Pg yr-1 (Zomer et al., 2009).
Although the area of AFS is not well documented in Ethiopia, it is estimated around 2.32 million ha (Brown et al., 2012).
In Ethiopia indigenous AFS are important sinks for carbon (Negash and Starr, 2015).
Reports showed that the area coverage of AFS with Khat increased by ha from 2007 to 2011 by replacing coffee based AFS in different parts of the country (Dubeet al., 2014; Wolduet al., 2015).
Farmers have gradually integrated the culture of growing khat into the once coffee-based production system. There has been a huge shift in land use with over 63 % of the total coffee land being uprooted and converted into khat (Woldu et al., 2015).
Objective
To evaluate the potential of biomass and soil carbon stocks of multi-strata agroforestry systems and Khat (Catha edulis) monoculture farming in Raya Azebo, Northern Ethiopia.
II. Biomass Carbon Stocks
The biomass models and organic matter contents presented can be used to predict the biomass and carbon density of khat plants grown in khat farming systems.
Conversion of CAF and FAF to Khat farming would reduce biomass C stocks on average by 60 % and 33 % of total ecosystem carbon stocks, respectively.
The tree (fruit plus non- fruit) biomass carbon shared % of total biomass C stocks in the study area.
This study revealed that maintaining coffee based and fruit based AFS would better serve of carbon accumulation than khat farming system.
Ongoing threats of observed human activities such as Khat expansion, limited tree density in smallholdings will likely diminish biomass carbon pools unless effective measures are enforced.
Promoting the shade trees in smallholding farmers, help to mitigate climate change. The government has to consider the use values of shade tree to conserve the AF ecosystem.
III. Soil Organic Carbon Stock
IV. Ecosystem Carbon Stocks for Studied System
References
Dube, D.K., Hiranmai, Y.R., Dube, S.K., Why a shift from coffee to chat? A study of the Kersaworeda in Jimma zone of South Western Ethiopia.Res HumanitSocSci, 4, 176–182.
Kuyah, S., Dietz, J., Catherine, M., Jamnadassa, R., Mwangi, P., Coe, R.,Neufeldt, H., 2012a.Allometric equations for estimating biomass in agricultural landscapes: I. Aboveground biomass. Agriculture, Ecosystems and Environment, 158, 216–224.
Kuyah, S., Dietz, J., Muthuria, C., Jamnadassa, R., Mwangi, P., Coe, R.,Neufeldta, H., 2012b.Allometric equations for estimating biomass in agricultural landscapes: II. Belowground biomass.Agriculture, Ecosystems and Environment 158, 225– 234.
Negash, M., Starr, M., Biomass and soil carbon stocks of indigenous agroforestry systems on the south-eastern Rift Valley escarpment, Ethiopia. Plant and Soil, 393,
The total ecosystem C stocks on average 157 Mg C ha-1 within 96 to 252 Mg C ha-1 across all the three AFS in all smallholdings.
The shift of AFS to KF would decline 33 – 32 % of C stock.