NORTH-SOUTH CENTRE - ETH - North-South Centre North-South ...

Mycorrhizas and maize yields in different
land-use systems in Southern Cameroon
Mycorrhizal symbiosis is commonly established by many
crop plant species and has the potential to improve plant
nutrition and resistance against diseases and parasites.
The mycorrhizal benefits can deteriorate due to changes
in the composition and/or activity of indigenous mycorrhizal
communities. Therefore, this project addressed whether
this deterioration could explain the rapid yield decline
occurring during cropping following forest clearance in the
humid tropics.
The project consisted of three modules. First, we carried
out a three-season field experiment with continuous maize
cropping on three sites close to the Metet village in Southern
Cameroon. These sites differed in their previous land use:
Cleared forest, chromolaena fallow, and continuously cropped
land. The set of trials addressed the effect of phosphorus
(P) fertilisation and the removal of mycorrhizal fungi by
application of fungicide (benomyl) on maize P acquisition,
biomass production and seed yield. Second, we carried out
a pot experiment with soils from the three different land
use systems sampled in Metet village. The soils were sterilised
and then inoculated with non-sterile soils – either from
the same land use or from different land uses. Some soils
were left non-inoculated. Maize was grown in pots and its
biomass production and P uptake was measured in order to
quantify the symbiotic benefits of the different indigenous
mycorrhizal communities grown on the different soils.
Third, we carried out a pot experiment with compartmented
cuvette containers and P radioisotope labelling,
addressing the extent of functional diversity among different
mycorrhizal fungal species co-occurring in the forest
soils of Southern Cameroon.
Both P and fungicide applications resulted in higher growth
and yields of maize in the field trials, with lower yields more
often found in continuously cropped than in fallowed or
cleared forest soils. The pot experiment with sterilised soil
showed significantly lower symbiotic benefits (support
of maize growth and P uptake) of the mycorrhizas from
cleared forest soil as compared to the mycorrhizas from the
chromolaena fallow or cropped land soils. Therefore, we
conclude that yield decline during the cropping sequence
following forest clearance cannot be attributed to declining
mycorrhizal benefits or mycorrhizal activity in continuously
cropped soils. This is valid in spite of the differences in functioning
of different mycorrhizal species as demonstrated in
the last experimental module.
Research fellow
Martin Jemo, IITA, Cameroon
71
Supervisors
Emmanuel Frossard and Jan Jansa,
ETH Zurich, Switzerland
Collaborators
Fritz Oehl, University of Basel, Switzerland;
Robert Abaidoo, IITA, Nigeria;
Dieudonné Nwaga and Adamou Souleymanou,
University of Yaoundé, Cameroon;
Jean Kuate, Institute of Agricultural Research
for Development, Cameroon
Duration
June 2007 – December 2009
Capacity development
Research fellowships
Flowering of maize in a P-fertilised plot in the third
cropping cycle on a previously forested area, Cameroon