I - --ii

Es x (1 - a) x Eo
t
where t is the number of days since it last rained, E. is the evaporative demand
and a is the fraction of ground cover. This formula demonstrates the importance,
not only of frequency of rainfall, but also the fraction of ground cover in determining
how much moisture loss in the evapotranspiration term is due to Soil
evaporation. We have previously noted the much greater greeni areas that were
obtained at the wetter sites (i.e. maximum values of 4.7, 2.6 and 1.7 for ILC 482
at Jindiress, Tel Hadya and Brida, respectively), and the implications that this
has on ground cover and radiant energy interception. Thus a progressively greater
proportion of the evapotranspiration loss occurred as soil evaporation as one
moved to the drier sites. Such moisture loss in not associated with assimilate
production and would result in lower WUE values.
Depth of Moisture Extraction by Chickpea
In traditional chickpea-growing areas chickpea crops usually follow wheat in the
local three course rotation system of wheat-grain legume (lentil or chickpea)summer
crop. At Jindiress and Tel Hadya, the trial was planted within this
rotation, but at Brida, the land was fallowed in the previous season. Previous
studies have shown that by the time the wheat crop reaches maturity, it has taken
up all the "extractable" soil 'moisture within the rooting profile, and that at
harvest very little moisture remains available for uptake. Further, slow loss of
moisture occurs by upward movement and surface evaporative loss during the
summer months. Thus during the next season only soil depth intervals which
become recharged by current rainfall will contain moisture which is available for
uptake by the chickpea. crop.
The distribution of soil moisture during profile recharge and discharge is given
in Figure IA, B, C, D, E, F for winter-sown ILC 482 at the three sites as an
example. It isclear that the chickpea crop was only able to extract moisture from
the soil profile from depth intervals which had been recharged by the current
season's rainfall. The results in Figure 1 are the mean of four replicates, but
examination of individual replicates indicated that there was a large betweenreplicate
variation in depth of profile recharge (Table 4) which resulted in
parallel variations in the maximum depth of observed moisture extraction. This
variation in depth of profile recharge is caused by large differences in the initial
moisture status of the profile. This within-treatment variation in depth of moisture
extraction was greatest at Jindiress, but also occurred to a lesser extent at
Tel Hadya and Brida. It is interesting to note that at Brida, where the chickpea
crop followed a fallow, much the same picture occurs (Figs. 1E and F). This
indicates that there was very little additional moisture stored in the fallow which
was available for the chickpea crop. In Figure IF, the dotted line represents the
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