Abstract:
The most important factors that influence germination and emergence are soil temperature and soil moisture.
Under optimum conditions of soil moisture, time of emergence can be predicted from heat units F:
F = (T - Tmin)t
where T is the mean soil temperature, Tmin is the minimum temperature for emergence and t is time (Fig. 1).
Under sub-optimum soil moisture conditions, germination is retarded by either 'too dry' or 'too wet'. The combined effect of temperature and soil moisture can then be modelled by 'effective' heat sums that are
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