Irrigation Optimization Using Remotely Sensed ETc and Soil Moisture Monitoring
What is Irrigation Optimization
The answer is hotly debated by academics, growers, agronomists, and irrigation industry experts. To keep it simple, let’s go with irrigation optimization is efficiently applying water in frequency and duration to precisely match soil properties with plant water consumption to ensure optimal crop yield. It’s about knowing how much water your crop consumed and how much evaporated, also known as crop evapotranspiration (ETc), along with how much moisture is in the soil. Once these parameters are known, a grower can irrigate just enough to replenish the water consumed and lost (ETc) at a rate that the soil can hold.
Why is Irrigation Optimization Important
This question appears to have an easy answer – water scarcity and enhanced sustainability, of course. There are very few geographical locations on the planet today that are not under pressure and, in many cases, regulations to reduce groundwater use for irrigation. California’s Sustainable Groundwater Management Act (see link to Beginners Guide: Sustainable Groundwater Management Act) is a good example where critically over-drafted water basin users must formulate and implement plans to become groundwater neutral (outflows = inflows) to achieve a sustainable balance. While many growers have improved irrigation system efficiency using drip, micro sprays, jets, etc., very few have adopted technology that would allow them to run their irrigation systems more optimally. It is widely accepted that most over irrigate using time-based schedules instead of a demand or replenishment approach.
Remotely sensed crop evapotranspiration (ETc) is readily available
State-of-the-art satellites observe crop water consumption and field evaporation are now capable of globe-scale coverage with 10-meter resolution (40 data points per acre) and revisit frequencies of 2-5 days. Field analytics showing ETc in inches of water per acre can be provided to growers weekly through services such as HyperGrowTM. This technology has been around for decades and is now refined and readily available to growers. The reason satellite-based ETc is so important is that it is specific to your field and crop, unlike methods using calculated ETc from remote weather stations that can be miles away from the field and crop coefficients that were developed decades ago. It’s not to say that these methods are bad or unacceptable, they’re simply not nearly as accurate or specific to the field.
Soil Moisture Monitoring is a Key Component
Soil moisture probes have been around and used by growers for many years. The idea here is to find a location in the field for the soil moisture probe that is considered marginal soil – not the best, not the worst. Chose a probe length that will cover the target moisture zone for the roots of the crop being monitored. This will give the best representation of the moisture in your soil profile. This concept is relatively well known, so we’ll use a couple of graphics to illustrate it.
By combining field-specific soil moisture information with satellite-based ETc, the grower can very precisely irrigate to replenish the water consumed in amounts and application rates to ensure the water is in the target moisture zone. Putting too much water on the field means it will run off or drop below the root zone where it is not available to the crop, not to mention it would be more than the plant’s consumption. Water savings are achievable year around, but the most significant savings come in the shoulder months of the spring and fall when ETc is lower (summer is peak ETc time). During these times, it is possible to take advantage of rain events and the soil’s water-holding capacity by significantly reducing or skipping irrigation altogether. Results vary depending on the crop, region, and grower practices, but we have seen 15% to over 30% reductions in applied irrigation water with no drop in crop yields. It is important to understand that these results are not from under irrigating the crop, but from reducing over-irrigation by more precisely irrigating to the plant’s needs and managing the soil moisture in the target zone.