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>Somebody knows where can I find references about the neutron probe?
>Specially in aspects of data analysis, for example how can I find the
>amount of water that it had been evaporated to percolated?, or How much of
>water the plant can take?
There are many hundreds of commercial users of the neutron probe and other
soil moisture sensors around the world. They tend not too publish, partly
because it is just 'part of the job' and they are too busy, but sometimes
because the data and conclusions are commercially sensitive and valuable.
The data analysis must be similar for any soil moisture measurements taken
at different depths. The VSW (%) at each depth is integrated ('summed')
over different depth ranges to get total water content. The rate of change
of water content in the active root zone can then be calculated and
distributed to...
surface evaporation
through-drainage
actual crop water use
The rate of change of water content can then be used to schedule the next
irrigation by calculating a date when the water content will fall to a
desired refill point.
The individual VSW readings plotted as soil moisture profiles give a clear
picture of root extraction patterns, over-irrigations and the onset of
stress - a virtual test pit. (e-pit ?)
Perhaps the most important soil moisture reading is that taken at a
sufficient depth (typically 120cm) where the soil moisture is constant -
where there are no changes. If this reading rises then through-drainage is
taking place; if it falls then the roots are starting to move downwards and
yield may be reducing.
Identifying through-drainage, and hence the full point, is difficult to
automate with software. Similarly with the refill point. In practice,
with real crops, the experience and skill from a grower is required to look
at the data and make informed decisions. When the full point has been
identified, a single sensor at depth could be used to automatically control
irrigation systems.
At the end of the season a grower will typically plot the actual cop water
use over the growing season of all fields/sites on a single graph. These
curves will be different from site-to-site, but by comparing this data with
pan or Et0 curves they can construct individual 'crop factors'. It is
interesting to compare these values with published crop factors.
By integrating the actual crop water use with time over the season they can
also calculate the total water volume used by the crop in each field,
compare that with the volume of water applied, and calculate the actual
water use efficiency for each site. In Australia, with a water shortage,
there are suggestions that WUE reporting become compulsory for all irrigators.
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Trevor Finch
Research Services New England
8/16 Nicholson Street
Balmain
NSW 2041
Australia
tel: +61 (2) 9810 3563
fax: +61 (2) 9810 3323
mailto:support@rsne.com.au
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