Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

for mucuna. Other important factors are maize grain·
price, Year 1 maize yield increment and year 2 maize
yield increment, in that order of importance.
For furmers who forgo maize production in the
investment year, the most critical element in
determining NPV is the maize yield forgone in both
countries. This is a cost element and as expected is
negatively related to NPV. This means that mucuna
adoption can easily be more attractive where forgone
maize yields are low and the converse is true.
Holding other factors constant, mucuna would be
more attractive on · those pieces of land where
continuously cropped maize yields are already very
low. For farmers who forgo maize production, maize
grain price is the least important determinant of
NPV. This means that an increase in the maize grain
price does not increase the attractiveness of investing
in mucuna for non-fallowing farmers as much as it
does for farmers who fallow land. This is because an
increase in maize grain price increases both the costs
and benefits of investing in mucuna technology for
non-fallowing farmers, hence minimizing the net
effect on the NPV.
Conclusions
The pay-offs to investing in mucuna as a green
manure in both Zimbabwe and Malawi were positive
though modest in magnitude for both categories of
smallholder farmers. After investing their labour and
some modest amount of cash to buy mucuna seed~,
farmers stand to gain a net present income worth an
additional 1.1 t ha-1of maize over th~ 3-year mucunamaize-maize
(investment-benefit-benefit) period in
Zimbabwe and 0.25 t ha- 1 in Malawi.
Although adoption of mucuna could generate higher
returns (positive NPVs), it is necessary to look into
the uncertainties inherent in the· NPV elemeiUS of
mu.c.una technology, such as maize yield responses,
prices and discounting rates. The study has shown
that the mucuna technology is not free from risk. The
risk of farmers encountering losses after investing in
mucuna was substantial for the category of farmers
who have to forgo one season of maize to grow
mucuna. The chances for farmers to realize negative
returns to their investment in mucuna were
calculated to be 30% in Zimbabwe and 38% in
Malawi. Mucuna has few other uses (the seed is not
edible) and so has a low monetary value. The risk of
negative returns can expose land-constrained farmers
to increased food insecurity. These two aspects of
mucuna technology could strongly deter its wide
adoption by smallholder farmers, many of whom are
land constrained and need to produce maize every
season.
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
The regression results from sensitivity analysis have
shown that the maize grain forgone had the greatest
influence on the expected NPVs for non-fallowing
farmers in both Zimbabwe and Malawi.
For such farmers, mucuna would give relatively
better pay-offs on lands where maize yields are very
low than where they are relatively high. In other
words, mucuna pays off better for the nonfallowing
farmers on those pieces of land where
they sacrifice little grain by choosing to plant
mucuna instead of maize.
This implies that minimizing the amount of maize
grain sacrificed by farmers in the first season would
increase PCly-offs of mucuna to land constrained
farmers. This calls for increased research efforts into
ways of minimizing the amount of maize forgone in
the first season for example by exploring intercrop
arrangements of mucuna with maize. Research
should also focus on improving the maize 'yield
response to mucuna incorporation and the
alternative end use possibilities for human
consumption.
Maize grain prices and discounting factors were
ranked the most important determinants of
expected NPVs for farmers who fallow in both
countries. Policy instruments can be used to make
these two economic parameters favorable for
mucuna adoption. For example, in Zimbabwe
where the cost of borrowing was very high,
reducing the discount rate has the most significant
effect in increasing attractiveness of investing in
mucuna by farmers who fallow ·land. In Malawi, a
policy measure to increase maize grain price would
easily increase incentives for investing in mucuna as
a soil fertility improving technology by those
farmers who fallow land. In both countries, a
combined effect of policy instruments to reduce the
discount rate and to increase the grain price of
maize would create more incentives for investing in
mucuna as a soil fertility technology.
Acknowledgements
The authors would like to acknowledge Webster
Sakala of DARTS, Malawi and Lucia Muza of the
Agronomy Institute, DR&SS for providing the
agronomic data used in this paper.
References
Buresh, RJ. and K.E. Giller, 1998. Strategies to reple~ish
soil fertility in African smallholder agriculture.
In: Waddington, S.R et al. (eds.) Soil Fertility
for Maize-Based Farming Systems in Malawi
and Zimbabwe. Proceedings of the Soil Fert Net
219