Frequently Asked Questions

To get optimal results from irrigated crop production, the irrigator must be able to predict the onset of plant water stress points. They must be able to calculate the amount of water lost from the root zone, to determine the volume to be applied at the next irrigation.

Quality, accurate, reliable technology is critical to be able to gain these facts.  Sentek soil moisture probes provide the data needed to make good decisions about how much water to apply, to support plant health, without wasting resources.

Not applying enough water, or applying water too infrequently will have a number of negative effects.  The growth, yield and quality of the crop will be restricted due to the effects of plant stress.  The crop’s ability to take up nutrients from fertilizer applications could be reduced, resulting in lower yields and wasted inputs.

As a plant moves into stress it also becomes more susceptible to pests and diseases.

Effective irrigation management is critical – as it impacts yields, quality and operating costs.

Applying too much water, or irrigating too often can also bring problems.  Water can be wasted either by runoff at the surface, or through excessive drainage past the active root zone.

Water logging, where the pores in the soil that normally allow air to be stored and exchanged are instead full of water, will slow down plant growth, and can encourage disease.  Valuable nutrients can also be leached.

At ground level, excess weeds may grow (adding further management costs), and clay and loam soils will have an increased risk of compaction – meaning machinery traffic will need to be reduced or stopped.

Operating costs associated with unnecessary fuel, water and labor expenses can be high.

There are additional environmental risks associated with rising water tables, salinity, and pollution from nutrient and pesticide run-off.

Increases in soil moisture can be attributed to:

• Irrigation
• Rainfall
• Overland flow from higher to lower lying areas
• Rising water tables

Decreases in soil moisture content can be attributed to:

• Water draining (gravity)
• Evaporating from soil surface
• Plants transpiring water

Smarter irrigation scheduling decisions can be made when the manager can identify the amount of soil water available in the root zone, monitor changes in levels at different depths, and understand the causes of the change.

Sentek provides the most effective method for measuring soil moisture, and has been the basis for impressive improvements in irrigation mangement strategies.

When numerical measures of soil water are recorded using continuous monitoring profiling probes – the data set allows analysis to determine not only what the soil moisture levels are, but what is causing them to change.

At the surface level, a rainfall gauge can help distinguish between rain and irrigation applications, but only a soil moisture probe can show you how much of that rain has moved through the soil to the roots of the crop.

Where rising water tables are increasing soil moisture, it can be easily identified using profiling probes, as it will start from the lower sensors.

By using continuous data rather than occasional readings, IrriMAX software allows the user to build pictures of changes at any depth in the root zone.  Water uptake by the plant at different depths can clearly be seen – and measured.   Further insights include calculation of water loss, that is water that is draining past the root zone and is wasted.

Over a growing season profiling probes such as EnviroSCAN and Drill & Drop provide valuable information regarding crop growth stages, so that  intelligent decisions regarding irrigation scheduling and fertilizer applications can me made.

IrriMAX has been developed by experienced soil water specialists for display of and understanding soil water and salinity dynamics. It is a powerful tool to graphically relate soil water and salinity data to the ever changing soil water plant atmosphere continuum, providing knowledge and insights. Graphical interpretation can then be readily converted to numerical analysis for final validation of irrigation scheduling results.

The raw data measured by your probe is converted via a calibration equation into volumetric soil water content. This is expressed as the volume of water per unit bulk volume of soil i.e. 1 mm = 1 mm height per square meter soil area = 1 litre.

If one sensor reads 1 mm, that means there is 1mm of water content in a 100mm thick soil slice on a volume basis. For that layer (and only that layer), this amounts to a volumetric soil water content of 1%.

Our probes are configured to operate at temperatures between -30°C and 85°C. While measuring frozen soil is possible, the dielectric properties of ice are significantly lower than water. Therefore measuring permafrost will yield low soil water content.

Some possible sources of water entry are a cracked access tube, or a broken/damaged seal in the bottom stopper or top cap. Pooled water inside the access tube can be removed with a water bailer. Next, use a clean rag attached to a pole to dry the inside of the tube, followed by another rag soaked in methylated spirits to clean the tube prior to reinserting your probe.

Sensor depths are usually determined by gathering site information about:

• Root zone depth
• Soil profiles
• Water tables

Generally speaking for Vegetable crops we recommend a 60cm probe length, and 90cm to 120cm for Trees and Vines.

In commercial operations, we recommend our factory default calibrations for sensors measuring relative changes in soil water dynamics. In applications where absolute volumetric soil water content is required, soil specific calibration of your probe is essential.

More information on how to calibrate Sentek probes can be found in out Calibration Manual.

A failed scan commonly occurs when the probe length is shorter than the depth of the profile. Verify that the soil profile is correct, and ensure the full depth of the profile is reached during the scan. If problem persists, check the condition of the probe cap or the cable connector for damage.

We recommend changing your silica gel bags every 12 months, depending on environmental conditions, or as soon as the crystals inside the bag turn pink. This change of colour indicates no more moisture can be absorbed by the bag and components are at risk of damage.

Each probe is fitted with multiple sensors located at a range of depths, these can be customized and changed as needed.  The probe rod is available at different lengths to suit a range of crops and monitoring situations.

The sensors utilize electrical capacitance to measure soil moisture.  The changing ration of air and water at each soil depth can be measured very quickly and accurately.

The sensor readings are converted to soil moisture using a calibration equation that takes into account the varying soil types.

A solar or battery powered logging system is connected by cable to the probes at each monitoring site.  Data can be logged at intervals as short as every one minute, and is downloaded or cloud uploaded to a computer or phone for display.

We are proud to provide our customers with an open integration platform for all SENTEK products. Our probes can connect to a range of 3rd party systems including:

• Data loggers
• Radio telemetry products
• Weather stations
• GPRS, 3G, CDMA and satellite communication modules
• Irrigation controllers

To get an estimate of your product’s battery life, click here to use SENTEK’s battery calculator.

The easiest method to check the status of your battery is to look at the voltage pane in IrriMAX software. The voltage at each upload interval is denoted by a red cross. If voltage readings are consistently recorded at 12v or lower, your battery is near the end of its life.

To prolong the life of your battery over multiple growing seasons, there are a few simple measures you can take:

For solar powered 12v batteries (RT6, Multi & Plus systems), maintain a continuous charge outside of the growing season.

For lithium battery packs (Plus All-In-One, Plus Compact systems), ensure the Dial-in Time (Logger tab, Probe Configuration Utility) is set to 0:00:00 when you configure your probe for the first time. When not in use, simply disconnect the battery from the probe. Depending on sample and upload rates, a lithium battery pack will power your probe between 1 – 2 years.

The maximum distance we recommend between an SDI-12 interface and your data logger is 60 metres with 22AWG / 3 conductor specification.

The maximum distance we recommend for use with an RS485 interface is up to 1km with 26AWG twisted-pair with correct termination.

The maximum distance we recommend for use with an RS232 interface is 5 metres, as tested by SENTEK at a 9600 baud rate. SENTEK cannot support systems modified beyond this tested configuration.

A relationship between volumetric ion content and EC1:5 or ECe can be made by plotting the average VIC against physical EC measurements using linear regression.

A spike is an unexpected change to a graph’s shape that often occurs due to environmental factors such as water entering the access tube, lightning strikes, or faulty hardware issues. Spikes can be removed from your data by using the Spike Remover utility.

Operating System: Windows 10, 8, 7, Vista

CPU: 900MHz (minimum)

Memory: 128MB

If your’re experiencing installation problems, ensure that any antivirus software or firewall settings aren’t conflicting with IrriMAX system files.

The Data Exchange utility  in IrriMAX software make it possible to transfer data to and from various IrriMAX sources and destinations. Data may be downloaded as a .csv text file or a .xls Excel spreadsheet.