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

SOIL FERTILITY IMPROVEMENT THROUGH THE USE OF GREEN
MANURE IN CENTRAL ZAMBIA
MOSES MWALE', CASSIM MASI 2 , J. KABONG0 2 and L. K. PHIRI'
1Mt. Makulu Central Research Station, PIB 7, Chilanga, genetics@zamnet.zm,
2World Vision International, P. O. Box 31083, Lusaka, Zambia
Abstract
Farmers identify low soil fertility as a major problem affecting crop production in Chibombo, Central Province, Zambia.
This means fertilizer is a prerequisite to crop production, particularly maize. But the use of fertilizer is not often viable
due to its high cost and poor availability. To boost crop production, there was need to test alternative cost-effective soil
fertility improvement techniques. An experiment was therefore conducted to reduce the soil fertility problem using
green manures. Sunnhemp (Crotalaria juncea) and Velvet beans (Mucuna pruriens) were grown either as sole crops
or intercropped with maize (in the 1998/99 season). Continuous maize (fertilized and unfertilized) and a natural grass
fallow were used as controls. Only phosphorus (50 kg PzOs ha·1) was applied to the unfertilized (zero nitrogen) maize
while compound 0 (10:20:10:8 : N P K S) at 100 kg ha·1 was applied to the other maize treatments. No fertilizers were
added to the green manure treatments. All maize plots (except unfertilized maize) were top dressed with urea at a rate
of 23 kg N ha- 1 . The dry matter yield of sunnhemp and velvet bean were determined just before flowering and all the
above ground biomass was ploughed under. The maize was harvested at physiological maturity and grain weight determined.
In the 1999/2000 season, maize was planted in all plots and cultural practices were the same as for 1998/99.
Unfertilized maize had the lowest dry matter and grain yield (less than 1 t ha- 1 ) followed by maize after the grass fallow.
All fertilized and green manure treatments yielded significantly more grain than unfertilized maize. There were no significant
differences (p=0.05) between the maize grown after the green manures and that which. received fertilizer. Incorporating
sunnhemp biomass not only increased the yield of maize but also increased the organic matter content of the
soil at the experimental sites.
Key words: Green manure, sunnhemp, velvet bean, profitability, sustainability, Zambia
Introduction
Low soil fertility is a major problem affecting crop
production in Chibombo District of Zambia's Central
Province. This has been made worse by farmers
who commonly monocrop with maize year after
year. This makes fertilizer use a prerequisite to crop
production, particularly maize. The current prices
of fertilizers are beyond the reach of most farmers in
the area due to liberalization of the economy and
the removal of fertilizer subsidies. The few that can
afford fertilizers have reduced their application
rates to far below those recommended, resulting in
low crop yield!> per unit area cropped . . This has affected
both food availability and income for many
people.
To boo~t crop production, there is a need to test alternative
cost-effective soil fertility improvement
techniques. An option identified by the farmers
through participatory rural appraisal (PRA) was the
'lse of green manures notably sunnhemp (Crotalaria
juncea), velvet bean (Mucuna pruriens) and some
agroforestry tree prunings such as Sesbania sesban.
These practices were part of the farming systems
before mineral fertilizers and most elderly farmers
still recall and appreciate the usefulness of the two
green manure species. Crotalaria and Mucuna have
shown to be excellent N2-fixers in a wide range of
enVironments (Bowen, et al. 1988; Kolar et al. 1993;
MacColl, 1990; Yost et al. 1985). Green manures
have the potential to accumulate up to 250 kg N ha- 1
yr-l (Giller and Wilson, 1991) resulting in cereal
grain yield increases of 600 - 4100 kg ha- 1 (Peoples
and Herridge, 1990). The use of a green manure
may also boost the levels of soil organic matter resulting
in improved soil structure, better root proliferation
and soil water holding capacity. This would
in tum increase crop vigour and yields. There is a
need therefore to evaluate the beneficial effects of
these green manures on farmers' fields in Muswishi
Agricultural Camp in Chibombo District and document
the results.
Project Objectives
The overall objective was to address the soil fertility
problem using green manures.
Grain Legumes and Green Manures for Soil Fertility in Southern Africa 173