RWANDA, LAND OF THOUSAND HILLS ...OF SOIL EROSION ...

Jules Rutebuka, A. Uwimanzi, O. Nkundwakazi, N. Ryken, A. VerdoodtDepartment of Soil Management

Steep, cropped fields in Rwanda

Siltation in the valleys, sand deposits

Effects of soil conservation practices on water erosion control in two agro-ecological zones of Rwanda

AND SOIL EROSION CONTROL

Jules Rutebuka, A. Uwimanzi, O. Nkundwakazi, N. Ryken, A. VerdoodtDepartment of Soil Management

Radical terraces

Progressive terraces

What is their effectiveness in terms of erosion control, soil quality and yield?

Does this effectiveness differ by agro-climatic zone?

RESEARCH QUESTIONS

Jules Rutebuka, A. Uwimanzi, O. Nkundwakazi, N. Ryken, A. VerdoodtDepartment of Soil Management

EXPERIMENTSTangata

Murehe

Erosion plots on radical terraces (RT)

Bare plots (BP), no control (NP)

Progressive terraces (PT)

Cropping seasons 2016A & BEvent-based monitoring soil lossSoil quality assessment

Buberuka Highlands (Tangata) are much more exposed to erosion than sloping areas of the Eastern plateau (Murehe).

PRELIMINARY RESULTSErosive events? Run-off coefficients? Soil losses?

Parameter Tangata 2016A

Tangata2016B

Murehe2016A

Murehe2016B

N° events 53 33 48 17

N° erosive events 6 5 4 5

Threshold erosive rainfall amount (mm) 15 16 25 25

Min. rainfall (mm) 3.5 3 1.2 1.3

Max.rainfall (mm) 36 26 46.8 46.4

Min. “intensity” (mm/hr) 7.8 4.5 4.4 4.8

Max. “intensity” (mm/hr) 54 60 208.8 26.7

Event-based results

Maximum run-off coefficient (%) 3.29-17.9 1.2-8.5 0.8-10.7 0.8-6.6

Maximum soil loss 0.01-39.2 0.01-5.6

Seasonal results

Run-off coefficient (%) 0.8- 4.6 0.6-2.9 0.3 - 1.8 0.4-2.5

Soil loss (ton/ha) 0.05 - 91.6 0.04 - 7.3

PRELIMINARY RESULTSRelative effectiveness of erosion control measures

Effectiveness of erosion control measure compared to non-protected land

Tangata 2016A

Tangata2016B

Murehe2016A

Murehe2016B

Progressive terraces

- Run-off % 47 40 -78 -65

- Soil loss % 98 -5

Radical terraces

- Run-off % 72 76 67 76

- Soil loss % 100% 93%

EFFECTIVE

EFFECTIVE

INEFFECTIVE

EFFECTIVE

RT plots are most effective to reduce runoff and soil loss while PT plots are only ineffective in Murehe due to installation and maintenance

PRELIMINARY RESULTSSoil quality effects of terracing?

Site Treatment SOC(%)

Ntot(%)

Exch. Ca(cmol+/kg)

Tangata NP 2.35±0.09a 0.18±0.01a 0.26±0.01a

RT 2.29±0.10a 0.17±0.01a 0.28±0.03a

PT 2.01±0.07b 0.15±0.01b 0.19±0.01b

Murehe NP 2.08±0.11a 0.21±0.01a 0.18±0.04a

RT 2.01±0.26ab 0.20±0.02a 0.29±0.10b

PT 1.87±0.15b 0.19±0.01a 0.18±0.01a

Soil quality is mainly influenced by plot history, past/current farmer’s management practices (fertilization, manuring). Indeed, terraces have no negative effect on soil quality status. Though the results are showing the impact of erosion control measures, These are still preliminary results that require some additional assessment

Thank You