April 2, 2014

Visualizing clogging up of soil pores in tropical degraded soils and their impact on green water productivity – A glimpse at NBDC science

Posted by Ewen Le Borgne under Books and Chapters, CRP5, East Africa, Ethiopia, IWMI, NBDC, Nile, Nile 4, Report, Water | Tags: , , |
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Restrictive soil layers commonly known as hardpans restrict water and airflow in the soil profile and impede plant root growth below the plough depth. Preventing hardpans to form or ameliorate existing hardpans will allow plants root more deeply, increase water infiltration and reduce runoff, all resulting in greater amounts of water available for the crop (i.e. green water). However, there has been a lack of research on understanding the influence of transported disturbed soil particles (colloids) from the surface to the subsurface to form restrictive soil layers, which is a common occurrence in degraded soils.

In this study, we investigated the effect of disturbed soil particles on clogging up of soil pores to form hardpans. Unsaturated sand column experiments were performed by applying 0.04 g/ml soil water solution in two sand textures. For each experiment, soil water solution infiltration process was visualized using a bright field microscope and soil particles remained in the sand column was quantified collecting and measuring leachate at the end of the experiment in the soil and water lab of Cornell University.

Preliminary results show that accumulation of significant amount of soil particles occur in between sand particles and at air water interfaces, indicating the clogging of soil pores occurs as a result of disturbed fine soil particles transported from the soil surface to the subsurface.

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See the full proceedings of the NBDC Science meeting

This paper was first presented at the Nile Basin Development Challenge Science meeting. The NBDC Science meeting was held on 9 and 10 July 2013 at the ILRI-Ethiopia campus, with the objectives to exchange experiences and research results across NBDC scientists involved in the NBDC projects and to discuss challenges and possible solutions.

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February 13, 2014

Synthesis of local knowledge on drivers of tree cover change in the Blue Nile basin – A glimpse at NBDC science

Posted by Ewen Le Borgne under Books and Chapters, CRP5, East Africa, Ethiopia, ICRAF, NBDC, Nile, Report | Tags: , , |
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The quantity and position of trees in a landscape can have significant impacts on farm soil and water resources.

Here we present a synthesis of local knowledge studies conducted in three micro-catchments of the Blue Nile Basin (Diga, Fogera and Jeldu Woredas) exploring natural and anthropogenic drivers of tree cover change. In total more than 90 purposively selected farmers were interviewed, whilst focus group discussions and feedback sessions were held with larger groups.

Local knowledge revealed that all three sites suffered from rapid deforestation of native tree cover over the last 20 years. All three systems were recognized by farmers as declining in agricultural productivity. The decline of native forest in Jeldu was found to be more rapid than the other two sites, partially due to market pressures from the capital city. Fogera and Diga were found to have remnant native forest still present, although certain tree species had disappeared completely due to over-exploitation for their products. This was associated with population expansion which has driven land cultivation into more marginal land (such as steeper slopes and marshy lowlands), resulting in land degradation and heightened pressure on common grazing land.

The farmers demonstrated detailed agro-ecological knowledge on how the physical attributes of trees impacted on water and soil resources. Farmers were able to describe the impacts of loss of native tree cover on erosion control, river bank stabilization, protection of headwaters and water quality improvements. There were knowledge gaps on how to integrate native trees into the cereal and horticultural cropping systems.

The research findings suggest some potential policy changes and intervention strategies to reach farmers and increase understanding of the functions of trees in watershed management according to on-farm niches and ecosystem service provisioning.

Read the paper

See the full proceedings of the NBDC Science meeting

This paper was first presented at the Nile Basin Development Challenge Science meeting. The NBDC Science meeting was held on 9 and 10 July 2013 at the ILRI-Ethiopia campus, with the objectives to exchange experiences and research results across NBDC scientists involved in the NBDC projects and to discuss challenges and possible solutions.

 

February 5, 2014

Effects of biochar and charcoal on soil-hydraulic properties – A glimpse at NBDC science

Posted by Ewen Le Borgne under Books and Chapters, CRP5, East Africa, Ethiopia, IWMI, NBDC, Nile, Nile 4, NRM, Presentation, Report | Tags: , , |
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Understanding soil hydraulic properties is crucial for planning effective soil and water management practices.

A study was conducted to evaluate the effects of different biochar and charcoal treatments on soil-hydraulic properties of agricultural soils. Biochar and charcoal treatments were applied on 54, undisturbed soil-columns, extracted from three-elevation ranges, with replications along three transects. Daily weight losses of freely draining soil-columns and soil moisture contents, at five tensions, were measured. In addition, field infiltration tests and soil analyses for particle size distribution, bulk-density and organic carbon content were conducted. Moreover, five year event precipitation data, from the watershed, was analysed and exceedance probability of rainfall intensity was computed.

Results show treatments reduced soil moisture contents, for most of the cases. However, treatment effects were significant only at lower tensions (10 and 30 kPa) and within two days after saturation (p<0.05). On the other hand, relative hydraulic conductivity (Kr) coefficients, near saturation, of amended soils were higher than the control. Acidic to moderately acidic soils with high average clay (42%) and low organic carbon contents (1.1%) were dominant. Infiltration rate ranged between 1.9 and 36 mm/h, with high variability (CV = 70%). At the same time, storms with short duration (< 15 min) and high average intensity (6.3 mm/h) contributed for 68% of annual precipitation (1616mm/year).

Dominant soil properties and rainfall characteristics suggest that infiltration could be a major problem on considerable number of fields, in the watershed. This implies, on such fields, constructing physical soil and water conservation structures alone will not reduce runoff and erosion effectively, unless soil infiltration and permeability rates are enhanced through integrated soil management approaches.

See the presentation:

Read the paper

See the full proceedings of the NBDC Science meeting

This paper was first presented at the Nile Basin Development Challenge Science meeting. The NBDC Science meeting was held on 9 and 10 July 2013 at the ILRI-Ethiopia campus, with the objectives to exchange experiences and research results across NBDC scientists involved in the NBDC projects and to discuss challenges and possible solutions.