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Benefits of cover crop legumes in
smallholder systems in Central America
In smallholder farming systems of the Nicaraguan hillsides,
intensification of land use has led to soil nutrient depletion
and a decrease in crop and livestock productivity. In order
to sustain the agricultural production, the drought-tolerant
cover legume Canavalia brasiliensis (canavalia) is being
introduced as green manure and forage into the maizebean-livestock
system.
Nitrogen (N) is the nutrient most limiting crop production
in the area. Canavalia represents a significant source of N.
However, when tested as green manure on farmers’ fields,
canavalia showed no effect on subsequent maize yields after
one year of rotation. This does not mean that residues
did not decompose and release N. Yet, their benefit to maize
remains unknown. An N dynamics study was set up in the
hillsides of Nicaragua in order to determine the N fertiliser
value of canavalia residues for maize. The direct 15 N-labelling
technique was used, where 15 N-labelled amendments
are added to an unlabelled soil in order to trace the fate
of amendment N in the soil-plant system. Microplots were
installed in three maize-canavalia rotation plots of a fiveyear-old
field trial. In June 2008, 15 N-labelled canavalia residues
and 15 N-labelled mineral fertiliser were applied on the
microplots. The microplots were then planted with maize
and harvested five months later. In average, maize took up
1.0 g N m -2 from canavalia residues and 2.6 g N m -2 from
mineral fertiliser, respectively, corresponding to N recovery
of 12% and 33% from amendment. Most of the amendment
N remained in the soil. At harvest, combined total
15
N recovery in both maize and soil was highest for canavalia
residues with 98%, followed by mineral fertiliser with
83%. These results show that canavalia residues represent a
valuable source of N for the subsequent maize crop. A part
of N in the residues is probably retained in specific soil
organic matter fractions, and will slowly become available
for crops with time.
Farmers’ perception of canavalia was studied using the
Structured Mental Model Approach. After one year of cultivation,
farmers testing canavalia realised that the cover
legume increases milk and maize yields, and generates
income. The study also showed that there is room for improvement
in the communication between legume specialists
and farmers. By increasing the knowledge of the farmers on
their own production system, sustainable adoption of canavalia
could be supported.
40 Project leaders
Emmanuel Frossard
Astrid Oberson
Contact person
Sabine Douxchamps
Research collaboration
Livestock systems research
Collaborators
Michael Kreuzer, ETH Zurich, Switzerland;
Idupulapati Rao, CIAT, Colombia;
Axel Schmidt and Rein van der Hoek, CIAT, Nicaragua;
Martin Mena and Alexander Benavidez, INTA, Nicaragua;
Claudia Binder, University of Graz, Austria
Duration
January 2007 – December 2009
Thematic cluster
Fodder resources and feeding strategies
Farmers and partners attending a
canavalia workshop, Nicaragua