RA 00015.pdf - OAR@ICRISAT

Table 68. Erosion on Vertisol and Alfisol watersheds
at ICRISAT Center, 1976.
Watershed Treatment Soil loss
Table 69. Soil erosion from first erosive storm
(90 mm on 21 Jul 1976) on an Alfisol at
ICRISAT Center.
Percent slope
Cultivation
method 0.4 1.0 Mean
Flat
Broad ridge
L.S.D. (0.05)
Groundwater
(kg/ha) (kg/ha)
852 1309
327 470
(kg/ha)
BW1 R / F , 0 . 6 7 % 800
BW2 R/F,0.6% 300
B W 3 A R/F, 0.4% 300
BW4A Flat, bunds 700
BW4B Flat, Gr. bunds 900
BW4C Fallow, bunds 9200
BW5B Fallow, R/F, 0.4% 3800
BW6A Flat, bunds 2200
BW6C/D Flat, C. bunds 200
BW8A Flat, bunds 500
R W 1 C Flat, Gr. bunds 2000
R W 1 D R/F, 0.6% 1800
RW1E Flat, C. bunds 400
RW2B R/F, 0.6% 2000
(kg/ha)
1081
399
365
Most groundwater levels, measured at piezometers,
indicate no substantial change between
May 1976 and May 1977 (Fig 85). An exception
is found where observations were taken near to
newly constructed Lake ICRISAT (BW8). On
deep Vertisols, the groundwater levels increased
by about 250 cm during the rainy season; this is
equivalent to approximately 160 mm of water. 11
Thus, about 25 percent of the seasonal rainfall
percolated through the root profile. On shallow
and medium deep Vertisols, the storage capacity
of the root profile is filled more rapidly and
therefore groundwater levels increase earlier
than in the deep Vertisols (Fig 85); the total
quantity percolated through the profile during
the rainy season amounted to about 265 mm, or
40 percent of the precipitation. On the shallow
Alfisol watersheds, the quantity of water lost to
groundwater can, from lysimeter observations,
be estimated at about 230 mm, or about 35
percent of the rainfall. Thus, even during a rainy
season of moderate total precipitation, very large
quantities of moisture may be lost from the root
zone particularly if, as in 1976, the duration of
the rainy season is short while the total seasonal
quantities are near normal.
Crop Season Evapotranspiration
Detailed data on evapotranspiration of several
crops during both seasons were collected by the
Soil Physics subprogram making use of lysimeters,
neutron moisture probes, and tensiometers
installed on watershed units (see page
144). The precipitation from 1 to 21 June (about
35 mm) did not contribute to plant growth,
although final presowing cultivation was facilitated.
The evapotranspiration of a sole maize (cv
Deccan Hybrid 101) crop of 100 days duration,
grown on deep Vertisols, was estimated at 350
mm; rainfall was well distributed and crops were
not subject to drought stress. Maize (cv SB-23)
grown as an intercrop in pigeonpea was of 93
days duration, and the evapotranspiration of the
intercrop combination was estimated at about
310 mm up to maize harvest time. No detailed
data were collected on medium deep and shallow
Vertisols; however, no serious wilting of crops
was observed and therefore similar figures may
be used. On the basis of lysimeter data from
medium deep Alfisols, it can be estimated that
11 The groundwater component is computed on the basis of
an estimated S % available storage capacity of the deep
subsoils.
186