In 1984, the rains in the second pea
season were below normal and poorly
distributed, resulting in very dry soils
at pod filling and a heavy attack of
aphids and powdery mildew. Based on
the same pea variety in the same field
at the same density in the previous
year, predicted pea yield could be
calculated from the regression
equations. Using the "normal" price of
peas (65 FBu/kg), predicted total
economic yield could also be
calculated. The conservative figure of
75% of the 1983 pea yield, or 1712
kg/ha, was taken as normal for the
field in question. The predicted total
economic yield as a function of maize
density of both varieties followed
identical binomial distributions (Figure
5). Total predicted protein yield,
calculated in a similar manner and
plotted as a function of maize density,
also followed a binomial distribution
for the two varieties (Figure 6).
Simple LERs, as a function of maize
density over two seasons for the two
maize varieties, followed a similar
Co
"1100
0
.21000
E
Cu
Co
S900
C.o
0
I-
0
- *
5 15 25 35 45 55
Maize density (000 plants/ha)
Figure 5. Predicted total yield of three
crops over two seasons as a function of
maize density
pattern of decreasing LER with
increasing density after a peak at low
density. This decline was less marked
for Igarama-4, regardless of whether
maximum yields for KCA or Igarama-4
were used as standardizing factors for
maize yield (Figure 7). With the yield
of KCA as the standardizing factor,
Igarama-4 had a higher LER over the
range of densities found in farmers'
fields (35 to 55,000 plants/ha). This
trend, though less striking, is also
present when Igarama-4 yield is the
standardizing factor.
The ELER might be a more
appropriate comparison of the two
varieties within this system, but it is
difficult to calculate since there are no
direct data available on the desired
proportion of the crops. Based on data
from this trial, however, one can
estimate from the average on-farm
maize density (approximately 45,000
plants/ha) that the desired crop
proportions within local constraints
(with a maize having a maturity such
as that of Igarama-4) would be 0.49 for
S340-
Co
S320 -
300-
c
t-
S280
Q.
o 260 -
0o
* 240
Co
Igarama-4
Kitale
5 15 25 35 45 55
Maize density (000 plants/ha)
Figure 6. Predicted total protein yield of
three crops over two seasons as a function
of maize density