| Summary: | Maize production plays an important socio-economic role in rural communities of the Highveld
region of South Africa, yet it is becoming increasingly difficult to produce maize economically
with current agricultural policy conditions and existing management systems. This has direct
socio-economic impacts for both commercial farmer and small-scale farmer. Sustainable
commercial maize production is not only a question of yields, but also of protection of the
environmental resource base, social welfare, and the livelihoods of farmers per se as well as
the surrounding rural and urban communities. Sustainability for the small-scale farmer, on the
other hand raises questions of equity, economic viability and household food security.
Therefore, information is required to ascertain whether an existing agro-ecosystem can be
identified as sustainable, and what facets of that system make it sustainable or
unsustainable. To begin to answer these key questions it is important to state, and to some
extent attempt to standardise, the definitions of agricultural sustainability.
Agro-ecosystem sustainability with regard to maize production was assessed at the regional
scale of the Highveld of South Africa as well as at, the Quaternary Catchment scale and the
smallholder farm scale. Von Wiren-Lehr's (2001) goal orientated system was considered an
appropriate and practical system by which agro-ecosystem sustainability across a range of
scales could be investigated.
At the regional scale, optimum management strategies for each of the 497 Quaternary
Catchments in the Highveld region were devised, based on present climatic conditions and
using an index which was based on mean yields and yield variability. Economic returns and
their impact on sustainability were then also assessed under plausible future climate
scenarios.
At the Quaternary Catchment scales optimum management strategies were ascertained by
using a sustainability index. These strategies were then modelled under present and
plausible future climate scenarios. The results from the sustainability modelling showed that a
maize crop will benefit, especially with respect to mean grain yields, from an effective
doubling of atmospheric CO2 concentrations. However, this benefit can be counteracted when
there is a concurrent increase in temperature, particularly of 2°C or more.
At the smallholder scale, a range of management options was assessed. These options
included several types of tillage practices in combination with applications of either inorganic
fertiliser or manure. The management strategies were modelled under present climate
conditions and under plausible climate change scenarios for southern Africa. The
conventional tillage type (disc) was ranked highest under most of the climatic conditions
modelled, including present climate conditions. This was in contrast to actual yields from
smallholder farmers (-1 ha field size) in the Potshini area, near Bergville in the KwaZuluNatal
province of South Africa, who have experienced an increase in yield when conservation
tillage practices have been used on their land (Smith et al., 2004).
The sustainability of agro-ecosystems depends on the maintenance of the economic,
biophysical and social components that make up the system (Belcher et al., 2004). The
modelling performed for the Highveld region built on previous work and for the first time
incorporated daily temperatures and ISCW soil information into CERES-Maize. The intention
was to incorporate other agro-ecosystem functions, as well as yield, into the sustainability
assessment. Only limited research has previously been carried out in South Africa with
respect to modelling smallholder agro-ecosystems and sustainability. This research sought to
model the smallholder system along with the impacts that climate change would have on
sustainability and associated food security. === Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
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