Chemistry Reference
In-Depth Information
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Figure 7
Maize grain yields from the outfield of the farm on the sandy soil amended
with 100 kg N ha
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and manure or single super phosphate in the first and
third season. Bars show SEDs.
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5 Soil Organic Matter Status and Quality as Affected
by ISFM
A last important issue of this chapter deals with the potential of ISFM to
enhance the soil organic matter (SOM) pool and the various services this pool
provides, including cation exchange capacity, rainfall infiltration, and soil
structure. Before addressing this issue, it is important to note that there is a
growing body of evidence that the longer-term impact of organic resource
quality (see section 3.1.) is not affecting the quantity or the quality of the soil
organic matter pool. In a field trial in Central Kenya, for instance, it was
demonstrated that litter quality did not influence longer-term SOC stabilisa-
tion (see Figure 8). Organic input addition was the only factor that influenced
SOM concentrations, although the inputs used varied widely in their N, lignin
and polyphenol contents, and covered the range of litter qualities commonly
available for field amendment in tropical agro-ecosystems. Regardless, these
differences in litter composition did not translate into differences in SOC
stabilisation. In other words, for increasing the SOM pool, application rates
are far more important than the quality of the organic inputs applied. An
exception to this trend appears to be manure or compost which tends to have a
larger proportion of its C retained in the SOM pool, probably because these
resources have passed through a decomposition process in the rumen of
livestock and/or after storage before field application.
