RA 00015.pdf - OAR@ICRISAT

the evapotranspiration for sorghum (CSH-6)
was approximately 340 mm; although sorghum
is of longer duration than maize, once dry
weather had set in during September, wilting was
observed in both sorghum and groundnut on
RW1 and RW2.
Beginning after the first week of September,
soil moisture levels started to decline and postrainy
season crops were sown under extremely
dry conditions; emergence was poor and stands
inadequate in nonirrigated areas. Newly planted
sorghum on deep Vertisols can be estimated to
have used about 200 mm of water (1.70 mm of
profile moisture and 30 mm of rainfall). Where
chickpea was sown on previously fallow deep
soils, or where it was irrigated (with about 60
mm) after planting, the evapotranspiration during
the postrainy season can be estimated at
approximately 180 mm. Chickpea sown as a
second crop without supplemental irrigation
may not have used more than 75 mm on the deep
Vertisols and even less on medium deep soils.
The evapotranspiration of a ratoon sorghum
crop on deep Vertisols amounted to less than 130
mm; on Alfisols, where the ratoon sorghum was
irrigated twice, only about 125 mm was used.
Pigeonpea grown on deep Vertisols used about
175 mm after the maize harvest.
The estimates of postrainy season evapotranspiration
on Vertisols do not include contributions
through upward water movement from
soil layers below 180 cm depth. There is some
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535
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531
. 0
Month
Medium to
shallow Vertisol
Deep Vertisol
M A M J J A S O N D J F M A M J
Figure 85. Comparison of seasonal changes in
groundwater levels in a medium to
shallow Vertisol and a deep Vertisol.
Surface elevation of the medium to
deep Vertisol is 533.02 meters; that of
the deep Vertisol is 537.82 meters.
evidence that this quantity, particularly in a dry
postrainy season like 1976, can be quite substantial.
From moisture data collected in June
1976 and May 1977, it appears that total profile
moisture up to 180 cm depth decreased by about
30 mm during this period.
In conclusion, total evapotranspiration of the
intercropping systems of maize and pigeonpea
can on deep Vertisols be estimated at about 485
mm (310 and 175). When sequential crops of
maize and chickpea were grown without irrigation,
the total evapotranspiration was 425 mm
(350 and 75); when the chickpea was supplementally
irrigated up, approximately 530 mm
(350 and 180) was used. In situations where only
a rainy season crop was grown on Vertisols,
seasonal evapotranspiration probably did not
exceed 400 mm even where somewhat longerduration
crops were used. Only approximately
200 mm was used if a single postrainy season
crop was grown. On Alfisols, the total evapotranspiration
of sorghum followed by an irrigated
ratoon crop was approximately 465 mm
(340 and 125). The evapotranspiration of a single
rainy season crop on Alfisols was about 340 mm.
Runoff Collection and Use
Substantial quantities of runoff occurred only
twice during the rainy season. In tanks with high
seepage rates - such as most of those on BW7 -
much of the water collected during the first
runoff event in July had disappeared by the time
high-intensity rains of sufficient duration occurred
again in August. A sequential crop of
chickpea was sown around 5 October on Vertisols
planted to sole maize in the rainy season.
Soil moisture had by this time receded to such
depths that planting into the moist zone by
animal-drawn equipment was successful in only
part of the watershed areas, thus very uneven
stands resulted. Because rainfall probabilities are
high in September and early October [the probability
of a wet week (20 mm) following a dry
week generally exceeds 50 % ] , supplemental irrigation
was delayed until mid-October.
When it was decided to apply water to chickpea
on Vertisols for germination and stand
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