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

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Questions and Answers
Rhizobium, N Fixation and Microbiology
To Sheunesu Mpepereki and Ishmael Pompi
Q: How did you handle marketing among
smallholder farmers?
A: In Zimbabwe, lucrative markets exist for
soyabean, e.g. for oil expression and livestock feeds.
Smallholder farmers come together in groups to
consolidate their harvest into large enough loads for
transport to market. (:ontracts have been negotiated
with buyers to accommodate all smallholder crops.
The Soyabean Promotion Task Force has played a
coordination role that has been progressively
passed on to farmers' own organizations. Private
buyers have supplied weigh scales.
Q: Is inoculation a full component of the soyabean
tedmology or do farmers often grow soya bean
without inoculation?
A: Yes inoculation is the key technology being
promoted. The inputs package contains seed,
inoculant, lime (for acid soils), base fertilizer and
fungicides (for rust disease). No farmer will plant
soyabean without rhizobia inoculants if they can
help it. Some plant promiscuous varieties.
Unfortunately, there is no breeding program for
promiscuous varieties in Zimbabwe.
Q: Where does the soyabean fit within the whole
farm system ~iven soil fertility gradients?
A: In Zimbabwe soyabean is planted in outfields,
often not the most fertile fields. Farmers are
encouraged to grow soyabean in the more fertile
fields to enhance yields and income from sales.
Q: What is the percentage of smallholder farmers
adopting soyab.ean production technology in
Zimbabwe?
A: Adoption rates have been near experiential.
Numbers increased from a few hundred to over 10
000 in three growing seasons (1996 -1999). Area
planted has increased from about 240 ha (1995) to 44
000 ha in 2000. In one communal area, Kazangarure,
with about 3000 families, AGRlTEX estimates over
98% have adopted soyabean BNF technology over a
four year period (1997 - 2000).
Q: To what extent could you have soil residual
effects of the inoculants in the field?
A: Residual effects of inoculants depend on the
survival and persistence of inoculation strains. In
heavy soils (with high clay and organic matter
content), rhizobia strains survive and are effective
for up to three seasons or more if the legume is
grown in a regular rotation. Survival and
persistence are poor in sandy soils where the
legume requires to be inoculated every time it is
planted.
To Friday Sikombe, et al.
Q: What were the optimum levels of nitrogen
fertilizers and inoculation for bean yields?
A: The optimum levels of nitrogen recommended
o
were 100 kg N ha ] which is called the Lima
recommendation. For the inoculum, the optimum
level is two 250g-packets of inoculant per hectare.
Q: The pH of the soils at your site was 7.2. What
could have been the effects on N- fixation? You also
applied N-fertilizers at two rates; 0 and 100 kg N
hao
]. Don't you think that 100 kg N hao
] was rather
too high and could have suppressed nodulation?
Do you think we have farmers who can apply
fertilizers at this rate?
A: The pH 7.2 had no effect on N- fixation. The
level of 100 kg N hao is the Lima recommendation.
This level did not affect nodulation except with the
cultivar, Lundazi. It is true that small-scale farmers
are unable to apply fertilizer nitrogen at this rate.
The option, therefore, is to exploit Biological
Nitrogen Fixation (BNF) through inoculation with
RhizobiJ, and the use of bean genotypes that
respond well to inoculation.
C: A rate of 100 kg N/ha is certainly too high for a
legume. Its effect would be to limit nodulation and
N fixation in the beans.
To Ylver Besmer, et al.
Q: Did you quantify the AMF inoculants, e.g. spore
numbers? And is the intervention one that f.umers
can introduce and manage?
Why lab lab? Does it h,l\'e any utility Y,11ue for
farmers or a chance of being integrated into the
cropping system?
Quantities of N from groundnut appear e:dremel~'
low, contrary to common knowledge that the
residues of groundnut have high amounts of N.
How do you explain this?
How did yOll account for Iitterfall by pigeonpe'l in
calculating N input?
How was the control for trapping the Aiv1F treated?
Grain legumes and Green Manures for Soil Fertility in Southern Africa
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