Soil Moisture Sensing Via Telemetry
Center pivot irrigation accounts for 40% of all
irrigated acreage in Missouri. There are approximately
4,000 pivots in the state, most
in the Bootheel. It is estimated that yields on
center pivots could be increased 10-15% if better
irrigation management, specifically irrigation
scheduling, were used. One viable scheduling
method is the use of soil moisture sensing (SMS)
devices, however, for a host of reasons Missouri
farmers are not using SMS. Missouri irrigators
would probably increase the use of SMS technology
if SMS data could be automatically collected
and made available to them at a
reasonable price. Telemetric SMS systems are
being tested at the Delta Center.
Irrigators in Missouri who do use irrigation
scheduling out-yield their counterparts who do
not schedule. Although use of soil moisture sensors
was only reported by 1% of corn growers
and 1% of cotton growers, the results from this
small sample were outstanding. Table 1 shows
the increased amount of yield enjoyed by irrigators
who employ the Arkansas Scheduler computer
program, the Woodruff charts, or soil
moisture sensing devices over their counterparts
who do not schedule their irrigation.
To properly use SMS on center pivots at least
three locations should be monitored to account
for distribution differences in the pivot. It is recommended
that each location have a 6-, 12-,
and an 18-inch sensor. Two types of sensors
seem to be feasible due to their cost, ease of use,
and reliability. These are WaterMarks and small
capacitance sensors. It is desired that no wires
be strung out in the field, so all communication
of data is done telemetrically.
Sensors are installed at the beginning of the
season after the crop has first emerged. Readings
from the sensors are sent telemetrically to
either the farmer’s own PC via repeaters or to a
website via cell phone modem. The University is
exploring developing a hosting site at its AgEBB
website. Figure 1 shows the components of a
SMS monitoring system hosted at the university.
The initial investment cost varies on company
used and whether the system sends data to
yourPC or to the web. A reliable system can be
set up for $3,000. The annual per-acre cost of
this setup would only be about $5.07 per acre
for the PC system or $6.79 per acre for the webbased
system. These costs would decrease if a
farmer has two or more pivots next to each
other.
If one compares those costs to the yield increases
farmers experience through irrigation
scheduling, it appears that this investment
could well pay for itself time and time again. Δ
DR. JOE HENGGELER: Ext. Assc. Prof., Biol. &
Agric. Eng. Dept., Commercial Ag. Program, University
of Missouri