Chemistry Reference
In-Depth Information
terms of land and labour, while their benefits are only seen in a following
season; and (iii) specific niches exist for herbaceous legume-based technologies,
for instance for the control of Imperata cylindrica L. weeds or the supply of
livestock feed, but their adoption has been very limited in scale notwithstand-
ing many years of investment and promotion. Cut-and-carry systems,
including Tithonia diversifolia (Hemsl.) A. Gray biomass transfer systems,
have the advantage that competition between the fallow species and the crop is
excluded, but the main disadvantage that additional labour is required to move
the organic inputs from their source to the cropped field.
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Grain legumes, such as cowpea or soybean, usually produce less biomass
and a significant amount of nutrient is removed with the harvested products,
but these are traditionally part of most cropping systems. Although improved
varieties of these grain legumes have a great potential to be adopted by
farmers, the earlier-developed germplasm contributed little to improving the
soil fertility status because their biomass accumulation was low and/or their N
harvest index was high and larger than the proportion of N fixed from the
atmosphere, leading to net negative contributions to the soil N balance.
However, over the past decade, grain legume breeding programmes have been
shifting from maximising grain yield alone to maximising grain yield and
fodder production - the so-called 'dual purpose' legumes. Such varieties
usually fixed more N than was exported with the grains and left a significant
amount of N in the soil to be potentially taken up by a following cereal. Such a
variety is, for example, TGX-1448-2E that produced between 470 and 2080 kg
grains ha
21
(average of 1290 ¡500 kg ha
21
) and between 1000 and 5340 kg
biomass ha
21
at peak biomass (average of 2510 ¡1050 kg ha
21
), and fixed
between 78% and 92% of its N (average of 84 ¡4%) when grown on 27
farmers' fields in Northern Nigeria. Not surprisingly, maize growing after
these improved soybean varieties had significantly higher grain yield (1.2-2.3-
fold increase) compared to a maize control.
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The most promising options in
terms of farmers' interest and adoption potential are based on the integration
of such multi-purpose grain legumes into existing farming systems either
through system adaptation, e.g. by adapting plant spacing to allow for higher
legume
d
n
1
r
2
n
g
|
5
densities,
or
diversification,
e.g.
through
inclusion
of
alternative
legumes.
22
4 Organic Matter Production and Use in the Context of
ISFM
Integrated Soil Fertility Management (ISFM) aims at intensifying agricultural
production through integration of essential and promising components,
thereby acknowledging the constraints smallholder farmers face in terms of
land, labour, and minimising modifications to existing farming systems.
Organic inputs are closely linked to ISFM in a several ways: (i) ISFM has the
potential to increase the availability of organic resources at farm level; (ii)
organic resources have the potential to enhance fertiliser use efficiency and
