Agriculture Reference
In-Depth Information
scape, social, and cultural heterogeneity will also influence the ability to transition to more
sustainable cropping systems.
There is ample evidence that the use of legumes, ideally in conjunction with some fer-
tilizer, provides significant benefits in terms of improved crop productivity in a vari-
ety of sub-Saharan Africa cropping systems. Less widely documented are measures of
changes in different aspects of soil quality, especially in terms of impacts on soil C and N
pools and microbial ecology, and how these relate to crop growth and nutrient cycling.
It is also apparent that there is great variability in the performance of legumes in differ-
ent systems and locations, leaving significant opportunities for improved management
to increase BNF and biomass production. Improved understanding of residue quality
and decomposition dynamics would also help to synchronize N release dynamics better
with crop demand.
The question of how to assess the relative sustainability of different management
options was discussed, framing sustainability as the ability to meet a combination of goals,
including immediate-term livelihood needs, food/income stability over time, and long-
term improvement of soil quality. This framing makes it clear that in addition to under-
standing system impacts on the biophysical components of an agroecosytem, it is critical
to consider the socioeconomic and cultural contexts where a system is targeted. These
arguments were illustrated through a case study of legume relay cropping in Malawi.
The case study provided a realistic assessment of the performance and sustainabil-
ity of different fertilizer and legume relay intercropped systems by testing them across a
representative range of smallholder farms in this region of Malawi. We used a framework
that examined sustainability as a combination of short-term livelihood benefits measured
as crop yields and net returns, farmer preference, adoptability, risk, and longer-term soil
fertility impacts, although we were limited in our ability to differentiate among the treat-
ments in terms of changes in soil fertility. While presenting some logistical challenges, the
project design allowed us to consider the effects of different landscape positions, resource
endowments, and gender on the desirability and sustainability of each system tested. By
considering variability across time and space, we obtained information on the risks of
low yields associated with each system. The incorporation of surveys, interviews, partici-
pant observation, and focus groups provided insights on the socioeconomic and cultural
realities of the participating farmers and their opinions of the systems being tested and
enabled a distributional assessment of performance to be made.
We found that relay intercropping maize with pigeon pea offered the most sustain-
able low-cost, low-risk option of the systems tested for improving food production and net
income for the poorest farmers. However, further improvements are needed to move these
farmers to greater food security. In contrast, any of the legumes plus a moderate amount of
fertilizer offered higher returns and benefits for wealthier farmers. Pigeon pea, however,
has the advantage of being a secondary food and a potentially valuable source of income
specifically for women.
For this, and other legume-based systems, a focus on improving legume manage-
ment to increase growth and BNF together with a better understanding of the dynamics of
residue decomposition, nutrient cycling, and SOM changes could greatly enhance system
productivity and sustainability. More effective use of legumes can help reduce risk and vul-
nerability to fertilizer price fluctuations by reducing fertilizer requirements and improv-
ing soil quality over the long term. The choice of systems to recommend needs to reflect
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