Evapotranspiration Monitoring Soil Moisture in Real Time By Christopher Sullivan

Do you know where your water is going? Sure, you know how long you run your pumps, how much water your irrigation system applies per hour and how much water your crop requires per season, but do you really know how effective your irrigation strategy is in delivering water and nutrients to your crop?

There are many techniques to evaluate the effectiveness of your irrigation strategy, ranging from digging a hole to inspect the feel and appearance of the soil to installing sensors to collect essential data from your field and deliver that data to you 24 hours a day, 7 days a week

A sensor measures the current state of the condition it is designed to measure — like temperature, humidity, wind speed and direction, rainfall amount, pressure of your irrigation system and soil moisture content. Locally collected weather data is necessary to calculate the evapotranspiration for that specific location instead of estimating ET for that location with weather service data possibly collected miles away from the field being managed.

ET is essentially the daily demand of water for your crop. Understanding ET is what allows the irrigation manager to schedule irrigation events and manage the supply of water available to the crop. Use of real-time soil moisture monitoring closes the loop for the irrigation manager by providing the feedback to validate the effectiveness of each irrigation event and ultimately compare the water applied to water loss.

The data collected from those sensors is the feedback that an irrigation manager can review to validate the effectiveness of each irrigation event and ultimately com- pare the water applied to water loss.

The next logical question is how often data should be collected to paint a meaningful picture of irrigation effectiveness? Is one time per week sufficient, like you would receive from a person physically evaluating soil samples, visiting sensors in the field to log soil moisture conditions, or collect-

Chris Sullivan is the general manager of Puresense, a subsidi-

ary of Jain Irrigation. Prior to joining Jain as director of supply chain in 2011, Chris held supply chain management positions in various industries. He has led the Puresense business since April 2015. Chris holds a B.S. from the University of Massa- chusetts and an MBA from the University of San Francisco.

ing soil moisture readings with a neutron probe? How about several times per hour, every day, every week?

If you were only collecting data one time per week, the increases in soil moisture (represented by the peaks on the blue real- time line) on June 17, June 24 and July 18 would be omitted from your data. Addition- ally, the dry soil conditions represented by the troughs on June 6 and July 4 would not be collected. As an irrigation scheduler with an incomplete data set, you could possibly make different irrigation decisions that could affect your crop quality and yield.

Another benefit of a real-time soil moisture monitoring system is the ability of the data analysis software to provide an irrigation manager with advanced analytics that can only be calculated with high frequency data collection and a soil moisture profile probe (a soil moisture probe with multiple sensors designed to collect data at multiple depths simultaneously). For example, infiltration is

tracking how long it takes water to pen- etrate the soil and reach lower depths, as recorded by the soil moisture probe. An irrigation manager with a clear understand- ing of how the infiltration rate can vary from block to block can customize the irrigation protocol for each block to ensure that water and nutrients are delivered to the root zone, and not pushed past the root zone by scheduling a longer irrigation set.

There are many other analytics that real- time data collection offers to help an irrigation manager develop a crop specific irrigation schedule to optimize crop inputs. A final indirect benefit is data collection and record keeping that can be used for regulatory compliance. As government agencies propose stricter reporting guide- lines to review how agriculture is managing water resources and nutrient application, the utilization of real-time crop monitoring and data collection software can streamline the preparation of compliance reporting. 19

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