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Real-Time Soil Moisture Monitoring
Real-Time soil moisture monitoring is a very beneficial tool to help optimize your irrigation scheduling. It will give you eyes in the field, even when you can’t be physically present. However, if not understood, the data can be overwhelming and even misleading. Having a company to help support your system is crucial in the success of the technology.
When monitoring with capacitance probes, it is important to focus on trends rather than the actual percentage reading. It is important to pull back your date range and look at the bigger picture to see where you have been before and where you are now. Doing this will display critical points specific to your field and your irrigation practices.
Here is a quick guide explaining several aspects of real time monitoring and how to better interpret your data.
Saturation– this is the point after an irrigation or rain event when all pores are filled with water. At this point water will freely drain through the profile due to the force of gravity pulling on the water, also known as gravitational water.
Field Capacity– once all gravitation water has freely drained we know we have hit field capacity at this level. This water is held to the soil particles with a force greater than that of gravity, but still available to the plant.
Onset of Stress– at this point the water is tightly bound to the soil particles and is unavailable to the plant.
Interpreting Your Graphs
1. Moisture readings will reach a plateau, meaning the soil can no longer take additional water. This is a visual indication that saturation has been reached.
2. The rapid drainage is the gravitational water leaving the profile. The change in slope then indicates when drainage stops and field capacity is reached.
3. This “stair stepping” pattern observed is the daily root uptake from the corp. A decreasing rate of change indicates less water is being pulled by the crop.
4. When the “stair step” pattern gets smaller and the slope of the graph appears more horizontal we recognize the crop can no longer pull readily available water, and onset of stress occurs.
One common concern is, “My probe is broken, I irrigate but I don’t see a the probe responding.” This is a valid concern and there are a couple things to check before replacing the probe.
1. Are you seeing any change whatsoever in readings, even a tenth of a percentage change. Normally when a system/probe is broken you will receive a “zero” value back or a static reading, meaning the same exact reading for a few hour period. Any change at all is a sign the system is working properly, even though it may net be the expected results. Next steps would be to investigate the situation in the field.
2. Once you verify there is “some” change in the readings, it is important to physically walk out to the field and check that the probe is in the wetting pattern when the field is being irrigated.
3. Lastly, make sure you are irrigating more than ETc for the given period. One common issue is the corp is pulling water as fast as you can put it on. In the example below, you can see the moisture status decreasing. When the first irrigation starts, the moisture status flat lines. This doesn’t mean you didn’t see moisture at this level, it means you didn’t gain moisture. The first irrigation event held the moisture level steady, meaning you applied the amount of water the crop was using but not more to refill. That is why we see the second irrigation event soon after starting to refill the profile.