"Oz" wrote in message
...
Gordon Couger writes

http://www.life.uiuc.edu/plantbio/wimovac/newpage11.htm
This model should work any where.

A splendid piece of work, pulling together a whole lot of useful stuff.

Getting the required parameters for a single UK field for a single year
of weather, though, would be a bit of a mission. If I were one of the
huge carrot growers on sand (eg round newmarket) I would get these guys
in to do soil analysis in depth for each field on the farm and install
remote weather equipment for each field or block.

Then a simple computer model would give me day-by-day information on the
irrigation need. Of course nobody else in the UK would be aware it was
even being done, let alone get a sight of the data.

There is work being done that will do just that. It is probably possible to
do it right now. The difficult part is the soil moisture sensor. For sandy
land I can make one that works but I don't think I can make one that doesn't
require individual calibration. It is a rather simple concept. A Whetstone
bridge wiht a thermosister in a substance very similar to the soil it is
buried in the solid and allow to come to equilibrium with the moisture in
the soil. It is powered up and the curve of tememerture plotted over time as
the resistor heats up with current going through it then shut it down. I
have built one and it works. But calibration is really bad news. The rest of
the parameter except humidity are real easy and humidity can be done.
Probably only soil & air temperature and moisture would be measured at the
remote sites. The central site would do all the other stuff you need unless
it was a really weird feild.

What we had in mind was use a 4 or 6 inch PVC pipe and bury it in the ground
with enough batteries to last a season and sense the soil conditions 4 or 5
times a day and transmit once or twice a day with a antenna on a light half
inch PVC pipe supporting an antenna that would go through a combine or any
other machinery with out damaging if some one forgot to pull one up at
harvest.

With today technology the cost of components would be about $200 USD. per
unit. I don't know what it would cost to do the design and implantation. It
depends on who does it.

There are defiantly people thinking about it.

Gordon