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

Table 3. N, P and Kconcentrations (means of ~ 5 samples) of indigenous legume species sampled identified species by farmers
from fields fallowed for asingle growing season in three smallholder farming areas across different themselves was fea-sible is
agro·regions in Zimbabwe
indicative of the potential to
Species Nutrient Concentration manipulate legume densities
in the stands, once the popu­
Chikwaka (NR II) Chinyika (NR III) Zimuto (NR IV)
lation dynamics are under­
'lioN %P %K %N %P %K %N %P %K stood. We consider Indifal­
Alysicarpus ovalifolius 1.53 0.04 0.73
lows as a technology for
Chamaecrista absus 1.19 0.11 0.77 those poor and vulnerable
C. rotundifolia 2.12 0.08 1.75 farmers for whom current
C. mimosoides 1.45 0.07 1.44 1.45 0.05 0.48 research and development
Crotalaria cylindrostachys 1.63 0.09 2.11 2.09 0.09 2.33 1.77 0.06 1.79 initiatives have failed to
C. laburnifolia 5.02 0.12 1.04 draw their participation.
C. microcarpa 2.09 0.08 1.71 .1.99 0.18 2.19 2.81 0.11 1.14
These poor groups often
C. pisicarpa 2.67 0.08 1.14
Eriosema ellipticum 1.62 0.05 0.99
lack minimal cash require­
Indigofera astragalina 1.95 0.08 0.89 1.62 0.14 2.16 1.18 0.04 0.33 ments to invest into cur­
I. demisa 1.81 0.10 1.28 rently available soil fertility
I. flavicans 1.71 0.05 1.29 technologies. The challenge,
I. praticola 1.74 0.13 1.14 however, is that of develop­
I. vicioides 1.41 0.07 1.75 2.59 0.11 1.24 ing strategies for integration
I. wildiana 2.38 0.10 0.84
of these legumes into exist­
Macrotyloma daltonii 1.66 0.06 1.14
Rothia hirsuta 1.59 0.09 1.72 1.91 0.10 2.44 1.66 0.06 1.02 ing cropping systems, and
Tephrosia longipes 1.32 0.05 0.33
defining the practical do­
T. purpurea 1.76 0.04 0.43 5.88 0.04 0.73 main within which the tech­
T. radicap~ 2.22 0.07 1.19 nology can work. The exis­
Vigna vexillata 1.65 0.06 1.40 tence of regional research
Zornia glochidiata 2.72 0.09 1.14 1.59 0.17 1.45 2.27 0.08 0.96 networks such as the TSBF­
Other weeds (mostly grasses) 0.75 0.07 0.73 0.63 0.07 1.35 0.69 0.05 0.59
CIA T African Network
I Each value·is a mean of four samples; NR - natural (agro·ecologicalJ region; H implies amissing value due to absence 01 (AfNet) and Soil Fertility
particular species in the sampling framework
Network for Maize-Based
1. Abundant seeding to allow ready propagation
Cropping Systems in Southern Africa (SoiIFertNet)
and ready seed collection to reinforce populaand
testing of Indifallow technologies on a regional
provide an opportunity for a wider development
tions.
basis.
2. A long-lived seed bank.
3. Rapid establishment and growth.
4. Adaptation to poor soils with restricted availability
of phosphorus.
Conclusions
5. Good N2-fixing potential in terms of spontaneous
nodulation with indigenous rhizobia, good Several conclusions were drawn based on this ex­
nodulation potential and high N concentrations ploratory study. Results showed that smallholder
in the shoots.
farming systems across different agro-ecological re­
6. Easy to remove by hand pulling or hoeing gions in Zimbabwe contain sufficient diversity of
should weeding be required.
indigenous herbaceous legumes to warrant more
The legumes thatbestfit these characteristics are STrategic research on Indifallows as a component of
largely annuals, biennials or short-lived perennials. integrated soil fertility management. However,
there are indications that that current clean weeding
Opportunities for Indifallows in small!:tolder practices recommended for these farmers may be
farming systems
contributing to loss of agro-biodiversity in farming
The potential for Indifallows lie1' in the existence of systems. Most of the dominant species were evia
diversity of annual legumes that can grow in their dently tolerant to poor fertility soils with low P and
mixtures with little demand for management of inon
pH levels, yet it was apparent that most of the soils
terspecific competition. Unlike agroforestry improved
fields fallowed by farmers in Zimbabwe are too
fallows and annual green manures, which poor to support any meaningful cropping using the
are often constrained by conditions of poor initial currently available low cost soil fertility technolo­
soil fertility, establishment costs and high labour gies. Although there is still need to establish why
demands, the most significant cost variables for In­ farmers have not significantly exploited these re­
difallows are likely to be seed collection and sow­ sources over time, we advocate for a paradigm shift
ing. The fact that seed collection for most of the in weed management approaches towards enhance-
Grain Legumes and Green Manures for Soil Fertility in Southern Africa 73