I - --ii

142
development in the interception of radiant energy, moisture use and productivity.
In all treatments, 60 kg/ha of P 20, and a Rhizobium slurry was applied with the
seed. This experiment was carried out at three sites which span the precipitation
gradient in Aleppo Province, na.aely, Jindiress (500-550 mm), Tel Hadya
(300-350 mm) and Brida (250-300 mm).
Samples were taken weekly from each site to provide a detailed growth analysis
of crop performance. Throughout the growth season soil profile moisture
status was monitored under all treatments using the neutron probe technique and
meteorological parameters including total incoming solar radiation, precipitation,
air temperature and pan evaporation were observed on site. Evapotransipration
(Et) for given time periods was determined by utilizing the data generated
from the neutron probe studies according to the equation:
E,= AM+P-R-D
where AM is the change in total moisture stored in 0- 180 cm profile in the
period considered, P is the recorded rainfall, R is the soil surface runoff and D is
the drainage below 180 cm depth. In this study, where all trial sites were flat,
runoff (R) was not a problem and drainage below 180 cm depth did not occur
(Fig. 1). Thus R and D could be ignored.
In addition, data are quoted in the paper for comparative purposes from a
companion experiment in which IC 482 was spring sown at the standard density
at all three sites. All other management treatments were similar to the wintersown
crop.
Results and Discussion
Phenology
Microscopic apical dissectiou has revealed that the reproductive phase is initiated
in ILC 482 approximately 10-14 days before it is initiated in ILC 72. From
Table I it can be seen that there is a uniformity of photoperiodic values within
each cultivar at initiation. This uniformity is not as closely matched in other
parameters that might influence the timing of reproductive initiation, such as
number of days from germipation, degree day accumulation or morphological
development (leaf number). Therefore it seems likely that in common with many
other crops, a specific photopcrik:dic threshold exists for each cultivar which
must be exceeded to permit initiation. These value, appear to be close to 10 hours
57 minutes for ILC 482 and 11 hours 24 minutes for IC 72 (both values exclude
civil twilight).