Agriculture Reference
In-Depth Information
the farmstead could produce satisfying yields on at least a small part of the farm.
This method has been widely used in Europe before the arrival of chemical fertil-
izers. Mtambanengwe and Mapfumo (2005) illustrate this approach, based on 120
farm field sites in Zimbabwe, reporting that manifestation of within-field soil fertil-
ity gradients on Lixisols and Arenosols under smallholder agriculture is primarily
a function of differential capacities by farmers to manage organic matter, which, in
turn, is driven by their resource endowment. Designated rich fields consistently con-
tain higher levels of organic matter than corresponding poor fields (or field sections),
apparently owing to cumulative effects of applying substantial amounts of organic
matter to such specific areas on a regular basis (e.g., Rusinamhodzi et al. 2013). This
has conceivably resulted in the formation of specific soil phenoforms that could act as
a “lighthouse”; however, no attention was paid to this type of interpretation. Tittonell
and Giller (2012) reach comparable conclusions when stating that differential man-
agement of the various fields of the farm led to the establishment of gradients of
soil fertility, notably decreasing with distance from the homestead. Farmers tended
to allocate their scarce nutrient and labor resources in the fields they perceived as
most fertile or less risky, or in fields around the homestead where high value crops
were better protected from marauding livestock or theft. A close interaction was
also found between soil fertility gradients and topography in these highly dissected
landscapes, with homesteads located on the upper positions of the slope. Such inter-
actions between inherent soil-landscape variability, historical and current manage-
ment, nutrient balances, and current soil fertility were documented for smallholder
systems in different parts of Africa, e.g., on Lixisols and Luvisols in Zimbabwe
(Zingore et al. 2008; Rusinamhodzi et al. 2013), where significantly different yields
were obtained between the two types of soil with comparable fertilization rates, and
Lixisols in Ghana (Adjei-Nsiah et al. 2008). Zingore et al. (2011) reported for highly
degraded Lixisols in Zimbabwe that restoring soil fertility required the application
of 10 tons of manure per hectare for 10 years before a maintenance rate of 5 tons/ha
could sustain productivity. This illustrates the major investment needed to reestab-
lish soil fertility of highly degraded soils.
2.3.2 n
itoSolS
and
v
ertiSolS
in
the
c
entral
h
ighlandS
of
e
thioPia
This case study is based on an experiment at Holetta Research Centre in the tropical
highlands of central Ethiopia (Assefa and Ledin 2001). The study serves to show
that, again, the soil type, fertilizer application, and crop variety are factors that
determine the yield and quality of the produce. The site is located at an elevation
of 2390 m above sea level; the mean air minimum is 6.1°C and the maximum is
21.9°C. Mean annual rainfall is 1100 mm. Trials were conducted on a red Nitosol
and a black Vertisol. Nitosols comprise among the most inherently productive tropi-
cal soils owing to their high nutrient status and deep, permeable structure, whereas
Vertisols show marked shrinking-and-swelling upon drying-wetting and poor physi-
cal properties, such as impeded drainage and poor workability when wet (Bridges
et
al
.
1998).
Three oats varieties (
Avena sativa
L.) and two vetch species (
Vicia villosa
and
Vicia dasycarpa
) were sown in monoculture and in mixtures in a randomized
