Re: soil moisture meter system required

[Jac le Roux <jac@besproeiing.co.za>]

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>I am a fruit farmer in the Western Cape area of South Africa. I am looking
>for a reasonably reliable method of measuring soil moisture that is easy to
>manage. Can you perhaps help me? Regards,
>Naas Terblanche
>
>De Pont Boerdery, Porterville, Western Cape, South Africa
>
Hi, my name is Jac le Roux, I have a company that does soil moisture
measurement and irrigation scheduling for irrigation farmers in the Western
Cape and would like to offer some pointers for Naas.

Having dealt with a number of soil moisture measuring devices I have come
to the following conclusions:

1. Tensiometers work well provided they are well installed and maintained.
I was amused though at how many growers using tensiometers will distrust
them and were willing to run another system parallel to them as a cross check.

2. Cheap capacitance sensors seem to work in sandy soils but run off the
scale in heavier soils. I know it's a matter of calibration; but my
ultimate feeling is that this is not the way to go if you are serious about
soil moisture and irrigation management.

3. If the application is critical, such as growing potatoes in sand (the
kind of sand where only a 4x4 will go) then a sophisticated TDR system such
as Enviroscan or Adcom is probably your best bet. This will give you real
time soil moisture variation and make it possible to optimise production
(provided the management is in place).

4. If you have a large number (20+ ?) of different fields, blocks, crops or
soil types  I suggest a portable probe such as a neutron probe, in
conjunction with an irrigation scheduling program (such as Probe Schedule,
Waterman or NPS). I am very fond of my neutron probe(s) because I can
calibrate it for the soil type I am dealing with and get results that are
marvelously repeatable.   It might seem odd that you could have control
over soil moisture and irrigation with sporadic measurements but if your
software can interpolate with some accuracy what happens between
measurements it is possible to come within 95% accuracy. This is the system
I use and can refer you to many satisfied growers who have either increased
yield by 20%, improved internal fruit quality or in the most extreme case
cut irrigation by 50%.

(The Probe Schedule program can be described as being "weather driven water
balance simulation with the built in capacity to have the water balance
checked and corrected by soil moisture or tension measurements". A more
detailed description and sample graphs can be viewed at: 
www.besproeiing.co.za/pse 

Jac le Roux, Cape Town, South Africa
jac@besproeiing.co.za