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

Soil carbon and nitrogen
Soil organic carbon content of the soils from the rich
fields in Chinyika ranged from about 4.5 (Classes B
and C fields) to 8.2 mg C g-l soil (Class A farmer)
while that from the poor fields ranged from 3.2
(Class B farmer) to 8.3 mg C g.l soil (Class A
farmer) . In five out of six cases, organic carbon was
consistently higher in the rich than the poor fields
(Figure la). The only exception observed was that of
a Class C farmer whose poor field had about 2.5 mg
g -1 soil more C than his rich field. Total soil nitrogen
was less than 1- mg N g.l ranging from 0.5 to 0.8
mg N g-l soil in Chinyika. There was little difference
in the soil nitrogen contents between rich and poor
fields in Chinyika for all the farmer classes (Figure
Ib). In Zimuto, soil C contents ranged between 2.0
(Class B farmer) and 11.5 mg C g.l soil (Class A
farmer) in rich fields and between 2.0 (Class C
farmer) and 8.2 mg C g-l soil (Class A farmer) in
poor fields (Figure 2a). Unlike the Chinyika case,
soil nitrogen was relatively higher in Zimuto, with
results ranging from 0.6 to 1.2 mg N g.l soil (Figure
2b). In all the selected field sites, the nitrogen content
of the rich fields was higher than that of the
poor fields regardless of farmer class.
Discussion
Ownership of resources was the key attribute differentiating
farmer classes. When it came to farm management,
the more resource-endowed Class A farmers
had more soil fertility options at their disposal.
The biophysical characterization of the smallholder
farming systems has shown that nutrient sources
accessible to farmers in the different agroecosystems
were highly heterogeneous and varied in quantity.
There was a general appreciation of the role of organic
nutrient sources in soil amelioration in the
three Natural Regions, particularly livestock manure_
However, it was Class A farmers who frequently
used mineral fertilizers for crop production
although they could afford to use other available
resources. Although there was widespread use of
manure among all classes, the survey also showed
that application of woodland litter, composted
household waste and crop residues to field crops
was deemed experimental by the innovator farmers
(Class B) and was also perceived as an option for
resource poor farmers. In many instances, manure,
when available, was preferentially applied to the
rich fields particularly by the Class A farmers. This
Chinyika (NR ·111)
12.---------------------------,-------,
.RiCh field
a) {2J Poor field
I - ·0.02; df - 9; p > 0.05
Zimuto (NR IV)
t - 1.89; df - 9; p > 0.05
.Rich field
EJPoor field
0>
.§.
'6 1 2 b)
'" t - 0.71; df - 9; p > 0.05
; 1
0>
E
:; 0 .8
::>
iii
"iii
z 0. 6
u
C
~0.4
o
MrCl MrC2 MrMI MrM2 MrZ MrW
Class A Class B Class C
Farme r' s name and class
Figure 1. Pre-season soil organic carbon (a) and nitrogen (b)
contents of rich and poor fields belonging to six three different
farmer groups in Chinyika, Zimbabwe
Mr Ml Mrs M2 Mrs C Mr Z Mrs T Clk);rstt
Class A
Class B
Farmer's name and class
Figure 2. Pre-season soil organic carbon (a) and nitrogen (b)
contents of rich and poor fields belonging to six three different
farmer groups in Zimuto, Zimbabwe
Grain Legumes and Green Manures for Soil Fertility in Southern Africa
61