Maize legume relay intercrops in Malawi - Microbial Ecology in Sustainable Agroecosystems - page 236

Forty-eight farm families, or households, were recruited for the initial project, selected
at random along six transects spaced 0.6 km apart. Eight households were no longer par-
ticipating in the project by 2004, and six other participants were either too old or ill to con-
sistently participate in all components of the socioeconomic data collection. The ethnicity
of participating farmers was predominantly Yao, with a minority from Chewa and Ngoni
ethnic groups. Forty-one percent of the households participating in the socioeconomic
analyses were female-headed households (FHHs), defined as households where women
were divorced, widowed, or separated from their husbands (Bezner Kerr, 2005).
9.5.2 Legume species
Prior to the project's initiation, University of Malawi, Bunda College of Agriculture
researchers held community meetings to ascertain farmers' assessments of local agricul-
tural constraints and opportunities. Soil fertility concerns predominated, and given high
fertilizer prices at the time, limited landholding sizes in the region, and the lack of access
to livestock manure, relay cropping of deep-rooted N-fixing legumes alongside maize
was identified as a research priority. All three AF species in this study are short-lived
deciduous shrubs of the family Leguminosae. Sesbania sesban generally grows between
4 and 8 m tall, while Tephrosia vogelii and pigeon pea ( Cajanus cajan ) are typically 1.3-3
m tall (Bunderson et al., 1995). Both T. vogelii and pigeon pea were cultivated in southern
Malawi prior to the project's inception. Pigeon pea is also a perennial grain legume, and
the seed is eaten to provide an important secondary protein source (Snapp, Blackie, et al.,
2003). Pigeon pea is the most common intercrop with maize in southern Malawi (Chirwa
et al., 2003). Farmers traditionally incorporated pigeon pea leafy biomass after the leaves
had senesced and fallen, but researchers also incorporated any fresh leafy biomass that
remained on the legume plants into the soil, leaving the woody portion to be used as fuel
wood at farmers' request. T. vogelii contains a toxic compound called tephrosin and histori-
cally was used to poison fish for consumption but had not previously been used as a green
manure. The farmers also had no prior experience cultivating S. sesban , but researchers
chose to include it in the study because it produces large amounts of biomass, and the
leaves can be used as green manure. The woody portions of all three legumes were used
by farmers as fuel wood.
9.5.3 Experimental design and management
The project encompassed two distinct experimental designs: design 1 (D1) from 1995 to
2000 and design 2 (D2) from 2001 to 2004 ( Figure 9.1 ). The designs primarily differed in
the rate and timing of inorganic fertilizer application. In 1995, four rain-fed plots were
established within each participating farmer's field; plots remained fixed in the same loca-
tion and position for the remainder of the project. At the onset of rains (typically in late
October or November), a maize hybrid was planted in each of the four plots and harvested
the following year. As is traditional in Malawi, three maize seeds were sown together, in
planting stations 90 cm apart on ridges also 90 cm apart. The legume species were planted
directly between maize stations. T. vogelii and pigeon pea seeds were each relay cropped
into one of the four plots within 2 weeks of maize planting, whereas due to a very low seed
germination rate, S. sesban seedlings were grown in a nursery and transplanted into the
third plot roughly 2 months after planting maize, one plant between each maize station.
The fourth plot served as the maize-only control; however, farmers generally intercropped
some plants in these plots.