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<pre>The figures of irrigation quoted for different world regions can only be
a guide only; the water requirements of your own plot could be quite
different. Influential factors include the rate of evapotranspiration
(ie loss by wind, sun), the depth of growing medium, the water holding
capacity of that medium, the style of irrigation (overhead, drip,
sprinkler, flood), cover crops, the quality of irrigation water, the
degree of the development of the plants root system. Take
evapotranspiration, which is normally calculated with an open pan
containing water left out in the open with the loss of water measured
daily. In NSW I have seen two nearby sites, 1 at Richmond Air Base & 1
at Hawkesbury Ag.(now UWS) with differing measurements for
evapotranspiration, probably due to the variation in microclimates.

I think the best method for irrigators would be to instal some sort of
soil moisture measuring device(s) to determine your own site
requirements.

Roger Farquhar

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