Effect of community-based soil and water conservation practices on soil glomalin, aggregate size distribution, aggregate stability and aggregate-associated organic carbon in northern highlands of Ethiopia

Welemariam M. K., et al., 2018. Agriculture and Food Security

Original research (primary data)
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Abstract

Background: Land degradation is a major and widespread problem causing losses of ecosystem services in Ethiopia. Extensive utilization of the land resources for centuries resulted in severe land degradation in the Tigray region of northern Ethiopia. To reverse the problem, land restoration activities have been carried out for the past three decades. This study was initiated to determine the effect of community-based soil and water conservation interventions on soil glomalin, aggregate size distribution, water stable aggregates (WSA) and aggregate-associated organic carbon. Methods: Soil samples were collected from exclosures + terraces, exclosures alone, stone terraces and non-conserved grazing lands using systematic sampling based on slope positions. Results: Both easily extractable glomalin and total glomalin were significantly (p < 0.05) higher in exclosures compared to terraces and non-conserved grazing lands. The macroaggregate fraction of all SWC measures ranged 21.91-32.41%, where the lowest was in non-conserved grazing lands, while the highest was in exclosures with terraces. The micro-aggregate fraction ranged 19.9-26.66%, where the lowest was in exclosures, while the highest was in non-conserved grazing lands. The results also indicated that exclosures had significantly (p < 0.05) higher percent of WSA compared to terraces and non-conserved grazing lands. Mean weight diameter (MWD) was also significantly (p < 0.05) higher in exclosures. The WSA and MWD decreased in the order of exclosures with terraces > exclosures alone > terracess > non-conserved communal grazing lands. Comparison of aggregate-associated organic carbon (AAOC) showed relatively higher organic carbon in macroaggregates than in micro-aggregates. Besides, both macro- and micro-aggregate-associated SOC was higher in exclosures than in terraces and non-conserved grazing lands. The AAOC of both macro- and micro-aggregates follows the order exclosures alone > exclosures + terraces > terraces > non-conserved communal grazing lands. Conclusion: Exclosures and terraces are important strategies for rehabilitation of degraded lands through improving glomalin content, aggregate structure and stability, and aggregate-associated organic carbon.

Case studies

Basic information

  • Case ID: INT-251-1
  • Intervention type: Combination
  • Intervention description:

    most commonly practiced SWC measures (i.e., terraces and exclosures with and without terraces) were established since 1997 by the community. Many of the SWC structures constructed are fully owned by the communities. is has contributed toward ensuring their sustainability (BoANR 2014). [coded for exclosures only] In the case of exclosures without terraces, there was no interference of livestock and human practices. Besides, no other management practices such as physical structures were observed. Trees regenerate naturally and hence better vegetation cover than terraces.

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced soil quality  Positive Soil erosion [positive] Soil fertility [positive] Same outcome measures for both: soil glomalin, aggregate size distribution, water stable aggregates (WSA) and aggregate-associated organic carbon. These measures were selected because they are an indicator of soil structure, functioning, stability, and resilience: “Aggregate stability is soil physical property consid- ered during restoration of degraded lands [17]. It is a measure of the ability of the soil to resist change due to environmental factors [18]. Soil organic carbon (SOC) and aggregate stability enhance vegetation growth [19]. e stability of soil aggregates in uences the water hold- ing capacity of soil and tells the susceptibility of the soil to erosion… Change in aggregate stability is an indicator of organic matter content, biological activity and nutrient cycling in soils [15] which are essential for the functioning of eco- systems… Soil glomalin forms soil aggregates and improves soil structure and stability against erosion [31, 32] as soils with stable aggregates are more resistant to erosion [33]. It is also source of active soil organic carbon [34] and contains 30–40% carbon [35]. e SOC associated with various aggregate size fractions reduces the impact of erosive forces [4] and tells the dynamics of soil organic matter… ”
    Soil erosion  Positive Soil erosion [positive] Soil fertility [positive] Same outcome measures for both: soil glomalin, aggregate size distribution, water stable aggregates (WSA) and aggregate-associated organic carbon. These measures were selected because they are an indicator of soil structure, functioning, stability, and resilience: “Aggregate stability is soil physical property consid- ered during restoration of degraded lands [17]. It is a measure of the ability of the soil to resist change due to environmental factors [18]. Soil organic carbon (SOC) and aggregate stability enhance vegetation growth [19]. e stability of soil aggregates in uences the water hold- ing capacity of soil and tells the susceptibility of the soil to erosion… Change in aggregate stability is an indicator of organic matter content, biological activity and nutrient cycling in soils [15] which are essential for the functioning of eco- systems… Soil glomalin forms soil aggregates and improves soil structure and stability against erosion [31, 32] as soils with stable aggregates are more resistant to erosion [33]. It is also source of active soil organic carbon [34] and contains 30–40% carbon [35]. e SOC associated with various aggregate size fractions reduces the impact of erosive forces [4] and tells the dynamics of soil organic matter… ”
  • Approach implemented in the field: Yes
  • Specific location:

    Degua Temben district, located 50 km west of Mekelle, regional capital of Tigray region, northern Ethiopia. Geographically, it is located at 13°16′23′′–13°47′44′′ latitude and 39°3′17′′–39°24′48′′ longitude (see Fig. 1).

  • Country: Ethiopia
  • Habitat/Biome type: Montane/Alpine |
  • Issue specific term: Not applicable

Evidence

  • Notes on intervention effectivness: "Effectiveness determined by comparing outcome measures to non-conserved communal grazing areas (acting as a control) Although some outcomes were the same between control and intervention, most were greater in the intervention (positive + no effect = positive) Mixed effectiveness compared to alternatives because for some measures, the engineered approach (stone terraces) or the hybrid (terraces + exclosures) were more effective than exclosures alone but in other measures, the reverse is true "
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Engineered approach(es) and other non-NbS approach(es)
  • Compare effectivness?: Yes
  • Compared to the non-NBS approach: Mixed
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: Please select
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures: n/a
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures: n/a
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: Yes
  • Experimental evalution done: In-situ/field
  • Non-experimental evalution done: Not applicable
  • Study is systematic: