Michael Percy writes

Noone has said anything about water demands. However, the specification is
rainfall when *you* demand it, (=rainfall demands) -- further specified as
1" rainfall when you have a 1" deficit. We understand that to mean you want
precipitation to track water loss closely. You estimate this will result
in a demand of 1" rainfall every three weeks in the summer, **typically**.

Indeed.
Strangely it depends how hot it is, hence the 'typically'.

Typical of what, summer 'as you know it', or the budget case?

Typical of a UK summer with normal variability, of course.

(The budget case would seem to attempt to utilize potential
evapotranspiration during summer to the fullest. In summer 'as you know
it', you are rainfed -- outside your control -- and you can't be utilizing
the potential evapotranspiration fully.)

Actually we normally run a deficit from about may/june until harvest.
Fortunately it's rarely more than 2" but when it's greater some of my
soiltypes start to suffer. Get to 4" deficit or so and yields start to
drop rather alarmingly if it's hot at the same time.

Most of my rainfall comes in winter, and heads northseawards having
passed through my field drains.

(Again, I didn't mean to interrupt, but you were just about to make an
estimate of the rainfall demands which would be necessary to balance the
evapotranspiration loss in the summer period. Do go on.)

Eh? Circa 7" would do. I've had reasonable yields with less, and
significant drought loss with more.

--
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