RA 00015.pdf - OAR@ICRISAT

grown in soil where pigeonpeas were grown the
previous year, the plants were stunted and unhealthy
and gave very poor yields. This year we
observed the same effect in some, but not all,
parts of ICRISAT Center. Other crops such as
sorghum, millet, and castor were unaffected.
This deleterious effect on pigeonpea growth
could not be brought about by adding pigeonpea
residues to normal soil, nor was the effect
reduced by removing pigeonpea residues from
soil when pigeonpea had been grown previously.
Therefore a toxic effect of pigeonpea residues can
be ruled out. We now have some preliminary
evidence that the harmful effects might be explained
by the build-up of parasitic nematodes.
This possibility is being investigated further.
Figure 30. Pigeonpeas planted in the postrainy
season are competitive in yield with
full-season pigeonpeas planted in June
or July. Cultivars of different maturity
are shown in an experiment in which
effects of planting date and spacing are
also studied.
Observations showed that nodulation and
nitrogenase activity of these winter-sown pigeonpeas
was much poorer than on those sown in the
rainy season. At 40 days after planting, nodules
per plant ranged from 6 for cv 7065 to 17 for cv
C - l l , which also had the greatest nitrogenase
activity of 4.68 µ moles C 2
H 4
, plant per hour.
Nodule efficiency - nitrogenase activity per unit
nodule weight - was also much lower than for
the rainy season planting, with most activity at
40 days (133 µ moles C 2
H 4
/g dry nodule per
hour for C-11). By 70 days, nitrogenase activity
was virtually nil. Insect grubs also attacked
nodules on this winter crop.
Residual Effects of
Pigeonpeas on Subsequent
Crops of Pigeonpea
Last year we found that when pigeonpeas were
Effects of N i t r o g e n Fertilizer
on Pigeonpea G r o w t h and
Y i e l d
Improved cereal pigeonpea intercropping systems
will almost certainly involve applying nitrogenous
fertilizer to the cereal. We investigated
the effects of a starter dose of 20 kg N ha as well
as a liberal dose of 200 kg N ha and 20 tons/ha of
farmyard manure on the growth. nodulation,
and yield of cv ICP-1 grown on Vertisol and on
Alfisol. Vegetative growth was increased significantly
by 200 kg N ha but nodulation and
nitrogenase activity, measured by the acetylenereduction
technique, was surprisingly little affected.
In Vertisol at 30 days after planting there
were 15 nodules per plant with 21 mg dry weight
for the 200 N treatment compared with 29 per
plant (52 mg) for no N fertilizer. At 60 days these
differences had disappeared. Nitrogenase activity
per plant followed the same pattern. Nodules
that formed, regardless of the N treatment,
were equally efficient in nitrogen fixation per g of
nodule.
However by the time of harvest, although the
nitrogen-fertilized plants had more stem material
and had produced more leaves, there were no
significant differences in grain yield. These results
indicate that yield was not being limited by
nitrogen supply.
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