28
capacity, and by reducing evaporation through lowering the soil’s surface temperature. A long-term experiment on Vertisol in Tigray showed that soil chemical properties such as organic carbon, nitrogen and soil microbial life were higher in
permanent raised bed compared to plots under conventional tillage (Areya et al.
2016). The soil’s physical properties such as aggregate stability, infiltration rate
(time to pond), penetration resistance and bulk density were also more favourable
under permanent raised beds compared to conventional tillage. This improvement in
soil’s physical properties will also make the soil less prone to erosion.
In the Rift Valley of Ethiopia, it was shown that soil volumetric content was
higher at the grain filling stage in mulched plots compared to non-mulched plots
(Sime et al. 2015). Mulching has been found critical in order to improve soil quality, as the amount of organic matter in the topsoil was twice as high in plots with
residue retention, compared to those with no retention of straw as mulch
(Baudron et al. 2015b).
Soil erosion is a great threat to the long-term productivity of Ethiopian soil. CA
is known to reduce erosion by improving water infiltration and by increasing resistance to erosion. Soil erosion was reduced from 30 t/ha in conventional tillage plots
without mulch to 16 Mg ha
−1
in zero tillage plots combined with 3 mg mulch ha
−1
(Adimassu et al. 2019) (average erosion across 3 years). However, zero tillage without mulch did not reduce soil erosion compared to conventional tillage. The soil loss
in CA plots with mulching is still quite high especially in erosion-prone areas. It is
therefore necessary to combine CA with other measures to control soil erosion.
Table 1 shows yield effect of convention tillage compared to different forms of
minimum tillage, with and without mulch. The tillage systems included were
reduced tillage, zero tillage with and without mulch, planting basins and permanent
raised beds. It appears that that there is no clear yield difference between conventional tillage and reduced tillage. Comparing conventional tillage to reduced tillage
gave an average yield change in percent of −4.0, +0.8 and −13.6% for maize, teff
and wheat, respectively. Zero tillage compared to conventional tillage in maize
reduced yield by 24.8%, and raised permanent beds in teff on Vertisol reduced yield
by 13.6% compared to conventional tillage. These results show that reduced tillage
could be an option for Ethiopian farmers, as this method maintains yield whilst
reducing production costs. Zero tillage seems to reduce yields compared to conventional tillage. There was a tendency for yields under zero tillage and reduced tillage
to improve over time compared to conventional tillage (Areya et al. 2016).
The effect of mulching on yield has been recorded of up to 3 Mg ha
−1
under
dryland conditions, whilst under more humid conditions, there is less impact of
mulching on yield (Baudron et al. 2014).
These results may underestimate the yield advantage of CA at the farm level.
Results from other African countries show that sowing is often delayed when conventional tillage is practised due to repeated tillage operations (Baudron et al.
2015b). This will inevitably penalise yield under conventional tillage.
Vertisols (heavy clay soils) are particularly prone to waterlogging. Farmers in
Ethiopia have traditionally used ridges or raised beds to reduce problems with
waterlogging on Vertisols, and research promoted further modification in traditional
J. B. Aune
capacity, and by reducing evaporation through lowering the soil’s surface temperature. A long-term experiment on Vertisol in Tigray showed that soil chemical properties such as organic carbon, nitrogen and soil microbial life were higher in
permanent raised bed compared to plots under conventional tillage (Areya et al.
2016). The soil’s physical properties such as aggregate stability, infiltration rate
(time to pond), penetration resistance and bulk density were also more favourable
under permanent raised beds compared to conventional tillage. This improvement in
soil’s physical properties will also make the soil less prone to erosion.
In the Rift Valley of Ethiopia, it was shown that soil volumetric content was
higher at the grain filling stage in mulched plots compared to non-mulched plots
(Sime et al. 2015). Mulching has been found critical in order to improve soil quality, as the amount of organic matter in the topsoil was twice as high in plots with
residue retention, compared to those with no retention of straw as mulch
(Baudron et al. 2015b).
Soil erosion is a great threat to the long-term productivity of Ethiopian soil. CA
is known to reduce erosion by improving water infiltration and by increasing resistance to erosion. Soil erosion was reduced from 30 t/ha in conventional tillage plots
without mulch to 16 Mg ha
−1
in zero tillage plots combined with 3 mg mulch ha
−1
(Adimassu et al. 2019) (average erosion across 3 years). However, zero tillage without mulch did not reduce soil erosion compared to conventional tillage. The soil loss
in CA plots with mulching is still quite high especially in erosion-prone areas. It is
therefore necessary to combine CA with other measures to control soil erosion.
Table 1 shows yield effect of convention tillage compared to different forms of
minimum tillage, with and without mulch. The tillage systems included were
reduced tillage, zero tillage with and without mulch, planting basins and permanent
raised beds. It appears that that there is no clear yield difference between conventional tillage and reduced tillage. Comparing conventional tillage to reduced tillage
gave an average yield change in percent of −4.0, +0.8 and −13.6% for maize, teff
and wheat, respectively. Zero tillage compared to conventional tillage in maize
reduced yield by 24.8%, and raised permanent beds in teff on Vertisol reduced yield
by 13.6% compared to conventional tillage. These results show that reduced tillage
could be an option for Ethiopian farmers, as this method maintains yield whilst
reducing production costs. Zero tillage seems to reduce yields compared to conventional tillage. There was a tendency for yields under zero tillage and reduced tillage
to improve over time compared to conventional tillage (Areya et al. 2016).
The effect of mulching on yield has been recorded of up to 3 Mg ha
−1
under
dryland conditions, whilst under more humid conditions, there is less impact of
mulching on yield (Baudron et al. 2014).
These results may underestimate the yield advantage of CA at the farm level.
Results from other African countries show that sowing is often delayed when conventional tillage is practised due to repeated tillage operations (Baudron et al.
2015b). This will inevitably penalise yield under conventional tillage.
Vertisols (heavy clay soils) are particularly prone to waterlogging. Farmers in
Ethiopia have traditionally used ridges or raised beds to reduce problems with
waterlogging on Vertisols, and research promoted further modification in traditional
J. B. Aune