Abstract:
Soil organic matter (SOM) is tightly
linked to soil quality, but cultivation generally causes
a decline in SOM, reducing soil quality and releasing
carbon dioxide into the atmosphere. Internationally,
countries are expected to reduce their greenhouse gas
(GHG) emissions, and compile and update GHG
inventories. Many developing countries, such as those
in southern Africa, do not have reliable information
regarding SOM levels in cultivated soils, changes over
time and best management practices to maintain or
even restore SOM. A review was conducted to collate
published research on SOM [or its indicator elements,
carbon (C) and nitrogen (N)] in cultivated fields in
southern Africa. A total of 84 publications were
assessed, and information such as date, location,
SOM/soil organic carbon (SOC) and clay content
and key findings were recorded. Most of the publications
(90 %) were published post-1990. The spatial
distribution of these studies is very non-uniform. A decline of 25–53 % in SOC due to cultivation was
evident for cultivated fields in different precipitation
zones in southern Africa, with SOC ranging from 0.7
to 2.5 %. These values correlate relatively well with
existing SOC maps. A strong correlation between
SOC and clay content in natural soil is weakened
following cultivation. Carbon sequestration and GHG
emission dynamics under various management systems
and for different climatic regions, as well as how
field crop production can play a role in mitigating
climate change, are poorly understood. Intensified
monitoring by multi-institutional collaboration is
recommended to address this issue.
