Why Not “Sense” Actual Water and Nutrient Use? Lysimeters for in-Situ Monitoring and Irrigation Management.

Lysimeters allow precise real-time data collection regarding water requirements of crops, yield response to environmental conditions, and fate of water, nutrients and contaminants. To date, utilization of lysimeters has been limited to determination of crop factors for use with meteorological data, as indicators of environmental contamination, or otherwise as research tools. 

We present design criteria for affordable lysimeters used in-situ in agricultural fields as sensors measuring actual water and solute balance components. Lysimeter design criteria are dictated by crop (dimension, depth), soil type (bottom boundary, drainage collection system), irrigation method (dimensions), and water management strategies (need for weighing or not).

We present examples for various crops (potatoes, peanuts, sorghum, corn) where lysimeters are used for monitoring actual evapotranspiration (ET) and fertilizer application efficiency or, alternatively, where they provide data to algorithms used to automate irrigation scheduling.

In a case study, high frequency irrigation was automatically applied to a corn field, based on hourly measurements of the ET from in-field weighing lysimeters. Seven daily irrigation events returned the measured ET plus a predetermined leaching fraction. Water storage, EC and the quantity of leachate water, and root-zone matric head were monitored in the lysimeter-irrigated plots and in control plots which were irrigated daily according to local practice (return of calculated ETc based on reference ET and crop factors). The automated irrigation by in-field lysimeters reduced both irrigation and drainage water quantities, while matching yield and ET measured in control plots. Over-irrigation is a rational response of growers since they lack reliable means for measuring actual crop water use. The investigated tool was found to increase water production efficiency of irrigated field crops while simultaneously decreasing agrochemical use and soil/groundwater contamination.