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

Table 2. Initial properties of soils at the two sites before the
start of the experiments
Parameter Champhira Nchenachena
Soil pH (1 :2.5 H2O) 5.3 5.26
Organic carbon % 0.56 1.032
Total nitrogen % 0.2 0.634
C:N Ratio 3.21 1.63
Mehlich·3 P(ppm) 0.054 0.078
Clay % 30.5 26.7
Silt % 8.3 13.3
Sand % 61.2 60.0
son and for maize stover orily at harvest for the second
season. Grain yield was also determined at 12.5
% moisture content at harvest of both seasons. During
the first growing season, only maize grain yield
was recorded. This was because Mucuna pruriens
and Tephrosia vogelii were incorporated at flowering,
when the crops attained their potential maximum
dry matter production. Pigeonpea grain yield was
very poor, mainly due to poor crop establishment,
and as such the available data were inadequate for
statistical analyses. The net plot from which yield
data was obtained was a four-metre section of two
of the innermost ridges from the five ridges of the
sub-sub plots i.e. 2 * 0.90 m * 4 m (7.2 m2). Rainfall
data was recorded from Champhira and Nchenachena
meteorological centres (Figure 1).
Treatment management
Agronomic operations 3uch as weeding, harvesting,
and sampling, was done at almost the same time for
each ·site. Planting was earlier in Champhira EPA
(within the 3 rd week of December) than in Nchenachena
EPA (2 nd week of January) owing to differences
in the onset of the rainy season between the
two sites (Fig. 1). In the first season, fertilizer was
applied two weeks after planting using 23:21 :0:4S
compound fertilizer. The rates were derived using
the following calculations:
From a 50 kg bag of fertilizer, there is 21 % P20S and
4 % S that translates to:
(0.21 * 50 kg) = 10.5 kg P20S. Similarly, for S = (0.04 *
50 kg) = 2 kg S.
Quantity to apply per unit area using the fertilizer
formulation at hand was obtained from the simple
proportion calculation below:
Example 20 kg P20S ha·1 treahnent
= (20 kg P20sha·1 * 50 kg bag-I) / 10.5 kg P20S bag- I
= 95 kg ha·1 of the fertilizer. In this there is approximately
4 kg S.
The fertilizer was banded along the ridge. Weeding
was done twice: before applying fertilizer and eight
weeks from planting.
In the second year of the trial, 50 kg N ha·1 was top
dressed using a high analysis straight fertilizer,
Urea, in all the maize.plots. To get the 50 kg N ha·I,
the following calculations were done: Each bag of
Urea has 46 % N,that translates to 23 kg N. The required
quantity =(50 kg N ha- 1 * 50 kg bag- 1 )/23 kg
bag- I = 108.7 kg ha·1 Urea. A banding method was
used.
The purpose of the second season was to evaluate
maize yield in response to the incorporated green
manure legume crops. The nutrients released from
decomposition of incorporated green manures were
expected to have a residual nutrient replenishment
effect.
Data from the experiment was statistically analyzed
using the Genstat 5 Release -3.2, (1995) computer
package.
Results and Discussion
First Season Results
Characterization of the soils at the two experimental
sites showed that soils at Nchenachena had higher
percent total nitrogen and organic carbon than soils
at ChamphiJ;"a (Table 2). The soils at Nchenachena
have been cultivated for less time than those at
Champhira.
Rainfall recorded during the study period. During
both growing seasons, Champhira received earlier
rainfall, but it stopped about one month earlier than
at Nchenachena. This meant different times of
planting at the two sites. Total annual rainfall was
higher at Nchenachena (932 mm) than Champhira
(558 mm) during the first season but in the second
season the difference was not substantial, i.e. 1061
mm for Champhira and 1120 mm for Nchenachena.
However, Champhira EPA received more rainfall
than normal during the second season (Figure 1).
Nitrogen and phosphorus in plant species at harvest.
The four crop species showed significant differences
(P= 0.001) in N content of their tissues at
harvest (Table 3). The highest mean was for TephrDsia
vogelii followed by Mucuna pruriens, Cajanus cajan
and Zea mays.
Leguminous crops fix ahnospheric nitrogen in their
tissues thereby ensuring the supply of this important
nutrient for their metabolism. Maize relies on
inherent soil nitrogen and the external supply of
this nutrient element. There were also Significant
differences (P < 0.05) in the content of phosphorus
of the four crops at harvest. Maize had the highest P
content followed by Tephrosia vogelii, Mucuna pruriens
and then pigeonpea (Table 3).
Grain legumes and Green Manures for Soil Fertility in Southern Africa
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