Agriculture Reference
In-Depth Information
give a lower yield and less economic return than conventional and reduced tillage
in nitosols and vertisols (Tulema et al. 2008). For wheat, there has been no clear
yield difference between CT, reduced tillage, and zero tillage; however, there was a
tendency for CT to give the highest yield (Taa et al. 2004). In Ethiopia, considerable
research has gone into developing different forms of raised seed beds in vertisols
to minimize the problems of waterlogging in this soil type (Nyssen et al. 2011).
However, although it has been shown that this is technically feasible, this form of
tillage has not been taken up by the farmers (Nyssen et al. 2011). Research on vertisol
has been conducted in recent years on more simple permanent raised beds that the
farmers can prepare with the maresha. The yield benefits of such permanent beds as
compared with CT in vertisols have become visible after 5 years (Araya et al. 2012).
The research on tillage methods in Ethiopia shows that there is no clear difference
in yield between the different tillage systems. This illustrates that reduced tillage
and zero tillage can be interesting alternatives in Ethiopia. The benefits here will
not be the increased yield, but rather the reduction in soil erosion and the possibility
of changing the livestock system more in the direction of meat- and milk-producing
animals, and placing less emphasis on keeping oxen for traction purposes.
A meta-analysis by Rusinamhodzi et al. (2011) across many countries of the world
showed that the effect of CA is most prominent in well-drained soil where an N level
of >100 kg N ha
-1
is applied. Mulching as practiced in CA may increase the problems
with waterlogging, and this is the reason why the best results with CA are obtained
on well-drained soil. Mulching with plant material with a high C/N ratio may cause
immobilization of N, and application of N rates >100 kg ha
−1
can minimize this
problem. CA has functioned best in dry years, and waterlogging has been found to
be a problem associated with CA in years of high rainfall (Rusinamhodzi et al. 2011;
Aune et al. 2012). Rusinamhodzi et al. (2011) found a positive effect of CA in areas
where the average rainfall is <600 mm; however, the effect of CA was negative in
areas with >1000 mm average rainfall. A study across Ethiopia, Kenya, Tanzania, and
Zambia also confirmed that the yield benefits of CA were highest in the driest years
(Rockström et al. 2009). This was the case although no mulch was applied in these
trials. This illustrates that ripping and basins can have a water-harvesting effect.
Practicing both CA and CT may therefore be considered by the famers as a risk-
aversion strategy as the CA will give a positive yield benefit in the dry years while
CT may give good results in years with high rainfall.
These results show that CA generally increased yield; however, there were clear
differences between countries and the tillage methods practiced. Planting basins
give the clearest yield benefits. Direct sowing and mulching as practiced in Malawi
also increased yields, but not to the same extent as planting basins in Zambia. The
benefits in Malawi were more connected to a reduction in labor.
10.2.2 l
Abor
U
sE
And
E
ConomiCs
of
CA
Changes in the tillage system also affect the labor demand and the distribution of
labor during the cropping season. A study in Zambia showed that the total labor
use during the entire season was 124, 145, 61, and 83 person-days ha
−1
for planting
basins, hand hoeing, plowing, and ripping, respectively (Umar et al. 2012). Another
