Oz wrote:

Michael Percy writes
Oz wrote:

Michael Percy writes

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

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

OK. I suspected that. Then those deficits are not realistic for your
budget case.

Que?

Because you are changing deficit management, causing change of actual
evapotranspiration.

I am not assuming a significant deficit (1", because that's better
for crop growth) , that's why I left 3" spare.

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.

That's it. The soil is normally in water deficit to a degree during your
summer, and the evapotranspiration suffers.

It's pretty well always between 1" and 2" deficit.
That's what happens if you have six weeks without rain.

Your intial specification for the budget case is 0-1".

In the budget case you have
changed that. Thinking you have enough water, and whenever you demand it,
you settle out to boost the evapotranspiration to the utmost.

Hardly, that wouldn;t give best yields.

You command the rain, you decide.

A deficit of about 1" (maybe rather more in late spring) is better.

Specification 1"rain when deficit is 1.5" replaces
specification 1" rain when deficit is 1".

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

That will change very much in the budget case.

Obviously. There is no requirement for a surplus rainfall wt 10".

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

Evapotranspiration losses cannot be limited to 7" during a summer typical
for UKs temperature and wind profile, while meeting the specification:
1" rain when you have 1" deficit.

So you say, I would beg to differ.

Evapotranspiration losses can also not be limited to 7" while meeting the
specification: 1" rain when you have 1.5" deficit. We have made you aware
of the problem. It is not a matter of opinion.

Mind you, anyone who says 'the UK temperature and wind profile' doesn't
know much about the UK.

I set your location to east anglia from the consideration that the climate
of the british Isles and european mainland would then need to be perturbed
the least. If you are interested i a swap, we have a well developed sight
in China with your preferred 10" rainfall in the summer, as specified. The
land is currently laid out in shrub and semi desert.

Mike