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creases rapidly and rainfall frequency decreases, that measurable differences in
E, and E. occur. This is an important point when comparing winter and spring
grown chickpeas since all root and shoot growth during winter is thus effectively
"free" in terms of moisture use.
In March, April and May there was little difference in evapotranspiration
between winter-sown crops at a given site, although the densely planted ILC 72
treatment tended to use more water than the standard density treatments. During
this period E, of winter-sown crops was significantly greater than the springsown
crops at all sites.
As winter-sown crops approached maturity at the two drier sites (Tel Hadya
and Brida) total E, values between germination and maturity were found to be
very similar in spite of the earlier maturity date of ILC 482. Nevertheless,
densely planted ILC 72 continued to have a slightly higher total moisture use
than either of the standard density treatments. In addition, at these two sites the
final total moisture use of the spring-sown crop was similar (though sightly lower)
to the winter-sown crops. In contrast, at the wettest site (Jindiress) where considerably
more moisture was stored in the soil profile (Fig. IA, B), the winter-sown
longer maturity ILC 72 used significantly more moisture than both the winterand
spring-sown ILC 482. This point is discussed in more detail in the next
section in which depth and efficiency of moisture extraction by chickpeas are
considered.
Utilizing the final harvest data (Table 7) the water-use efficiency (WUE) of
both total drymatter and seed production was calculated in terms of kg/ha/mm
of moisture used. Considering WUE of total drymatter production, it can be seen
from Table 3 that the densely planted ILC 72 and winter-sown ILC 482 treatments
achieved very similar WUE values at any given site, but were higher than
the standard density ILC 72 treatment. All winter-sown crops achieved much
greater WUE values than those obtained for the spring-sown crops, particularly
at the two wettest sites, Jindiress and Tel Hadya.
In terms of seed yield also, the winter planting of ILC 482 achieved a far
higher water-use efficiency than the spring sowing resulting in a 119, 150 and a
32% increase in WUE at Jindiress, Tel Hadya and Brida, respectively. Due to the
very different harvest index of the erect and spreading cultivars, the spreading
cultivar gave a consistently better WUE than the erect types at all sites.
Comparing the WUE for an individual treatment across sites for both total
drymatter production and seed yield, it is interesting to note the general decrease
in WUE as one moves from wettest to driest site. This is partly due to differential
stress during the period of potential flower and seed abortion resulting in a
tendency for lower harvest indices at the drier sites, but it is likely to be attributed
more to the differential ground cover achieved at each site. The moisture loss
due to E, (soil surface evaporation) can be calculated on a daily basis from the
empirical formula: