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30<br />
0<br />
Moisture content (volumetric basis)<br />
0.20 0.24 0.28 0.32 0.36 0.40 0.44<br />
45<br />
60<br />
75<br />
90<br />
105<br />
120<br />
135<br />
150<br />
165<br />
Full capacity<br />
Initial 9 Nov<br />
Final 23 Feb<br />
30<br />
60<br />
90<br />
120<br />
150<br />
180<br />
210<br />
Fallow<br />
Pigeonpea<br />
Chickpea<br />
Safflower<br />
Figure 66. Moisture profiles at crop harvest in<br />
deep Vertisols.<br />
180<br />
32 .34 .36 .38 .40 .42<br />
Volumetric water content<br />
A : Initially recharged soil profile<br />
B : Partially recharged soil profile<br />
Figure 65. Initial and final moisture profiles of<br />
differentially charged soil profiles.<br />
postrainy season crops of pigeonpea, chickpea,<br />
and safflower. The end-of-season profiles (Fig<br />
66) reveal that the surface 30 cm was depleted<br />
below the 15-bar percentage. In the 30- to 180-cm<br />
section, slopes of the residual moisture profile<br />
were roughly the same for the different crops.<br />
About 40 percent of the "available" water (field<br />
capacity minus 15-bar percentage) in the 30- to<br />
180-cm section was not used by the crops. It is<br />
suggested that this end-of-season moisture profile<br />
may be a better indicator of the "crop<br />
extractable" water on deep Vertisols than the<br />
traditionally used "available" water.<br />
Assuming that the deep Vertisol profile was<br />
fully charged at the beginning of the season, 115<br />
mm was used by the postrainy season crops, 40<br />
mm was lost by evaporation, and 50 mm was left<br />
as residual moisture in the 30- to 150-cm section.<br />
The 0- to 30-cm layer lost about 50 mm, much of<br />
it by evaporation. An unmeasured but perhaps<br />
agronomically significant amount of moisture is<br />
believed to have moved upwards into the rooting<br />
zone from depths below 180 cm. This assumption<br />
is supported by tensiometer data that showed<br />
upward hydraulic gradients in excess of five times<br />
gravity in the 150- to 180-cm section during<br />
extended periods of time beginning in<br />
November.<br />
Conclusions<br />
From the experiments conducted and data obtained<br />
during the past year, it was concluded that<br />
the physical properties and processes which<br />
govern the retention and movement of water in<br />
the soil-plant-atmosphere continuum can be<br />
measured with reasonable precision. These<br />
measurements can be used for field studies of the<br />
water balance, time and depth pattern of profilewater<br />
depletion, and crop water-use efficiencies<br />
on the deep Vertisols; however, further work will<br />
be required to develop means of coping with the<br />
145
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