Evaluation of selected grass species for soil and water conservation, and carbon sequestration under farmland at Jimma zone, southwestern Ethiopia

Résumé

The objective of this study was to evaluate the effects of different grass species on soil and water conservation and carbon sequestration at a farmland in Jimma, Ethiopia. The experiment was set out as a randomized complete block design with three replications. The treatments were vetiver grass ( Chrysopogon zizanioides L.), Desho grass ( Pennisetum pedicellatum ), Phalaris grass ( Phalaris arundinacea L.) hedgerows, and the control (plots without grass). Soil erosion monitoring pins were installed, and the data were collected every 15 days. Soil samples were collected at 20 cm intervals in the top 100 cm before the grass hedgerows’ establishment and after harvesting seasons in December (2016–2019 G. C.). Fresh and oven-dry matter biomass (shoot and root) data were measured. The collected soil samples and grass biomass analysis for carbon fraction were determined following Wakley and Black (1934) and the loss on ignition standard procedure methods, respectively. Pin heights and soil moisture data were analyzed using R software. Results show that, significantly ( p < 0.05), the highest mean value of pin height was observed in a control plot as compared to plots with grass species. Conversely, soil moisture and crop yield showed no significant variation between treatments. However, the highest mean value of soil moisture content was exhibited under the plot with the vetiver grass hedgerow. Vetiver grass possesses the highest potential for carbon content in the shoot (22.06 Mg C ha-1 yr-1), root (8.98 Mg C ha-1 yr-1), and soil (15.9 Mg C ha-1 yr-1). Furthermore, the Vetiver grass sequesters (172.27 Mg C ha-1 yr-1) more carbon as compared to Desho grass (112.85 Mg C ha-1 yr-1), Phalaris grass (78.35 Mg C ha-1 yr-1), and plots without grass species (44.41 Mg C ha-1 yr-1). This study suggests vetiver grass for soil and water conservation and carbon sequestration purposes to contribute to the mitigation of climate change. Further study of the potential of grass species on carbon sequestration under controlled experimental plots is encouraged since collecting fibrous root biomass is difficult on farmlands.

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