The climate analysis results (1954–2014) indicated that the earlier the planting date the greater the risk of encountering periods of
cold and frost at both Narrabri and Griffith (Fig. 6a,b). The number of
cold days (from 6.5 to 3) and frost (from 2.4 to 0) decreased substantially around the normal target plant date of mid-October. Earlier
planting with film also resulted in earlier emergence (15 days vs
40–25 days) compared with bare soil (Fig. 6c,d). This suggests that
the seedlings which emerged early would be more likely exposed to
cold and frost. The combination of early planting and the potential
for cold and frost occurrence reduced lint yield and crop survival.
As the planting date was delayed, lint yield decreased but crop failure was less likely. When the frost function was disengaged in the
OZCOT model all crops survived to produce lint yield (Table 6). With
the frost function engaged, early planted crops (August) which did
survive produced slightly more lint yield under film compared with
a bare planting at Narrabri (100 and 96% of yield potential) while
early planted crops at Griffith (week 1 and 2 August planting) did
not survive through to harvest (0% of yield potential) (Table 6).
Yield reductions ranged from 1 to 7% of yield potential due to early
planted crops experiencing a period of cold weather or frost post
emergence. This was more pronounced at Griffith than at Narrabri.