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