A Soil Moisture Sensor-Based Variable Rate Irrigation Scheduling System.

Over the past two decades, irrigation has become essential to crop production in many agricultural areas of the United States.  As a result, the competition for available fresh water supplies is increasing.  Ugly political and legal battles between competing users to secure access to water are taking place all across the United States – even in the humid southeastern region of the country where annual precipitation exceeds 1300 mm.  If irrigated agriculture is to survive in this competitive environment, we must use irrigation water efficiently.  Precision irrigation offers the potential for improving irrigation efficiency.

To quantify the potential of precision irrigation, we began a research and demonstration project whose goal is to develop a soil moisture sensor-based variable rate irrigation (VRI) scheduling system.  The control system consists of a wireless soil moisture sensing array with a high density of sensor nodes, a VRI enabled center pivot irrigation system, and a web-based user interface.  The operational paradigm is that the field is divided into irrigation management zones; the soil moisture sensing array is installed to monitor soil condition within the zones and provides hourly soil moisture measurements to the web-based user interface.  At the interface, the soil moisture data are used by an irrigation scheduling model running in the background to develop irrigation scheduling recommendations by zone.  The recommendations are then approved by the user (farmer) and downloaded to the VRI controller on the center pivot as a precision irrigation prescription.  When the center pivot irrigation system is engaged by the farmer, the pivot applies the recommended rates. 

The project began during the spring of 2012.  The soil moisture sensing system was deployed in eight demonstration fields with a minimum of ten sensor nodes per field.  Field size averaged 80 ha.  Soil moisture data were collected hourly with the University of Georgia Smart Sensor Array (UGA SSA) for the entire growing season and streamed to a web server where they were displayed.  The soil water tension graphs created from the data on the web server show very different soil water moisture conditions between zones within fields confirming that VRI can improve efficiency.  The graphs also show dramatically different soil moisture conditions between fields indicating that some farmers are over-irrigating while others are under-irrigating. 

All center pivot irrigation systems in the demonstration fields were equipped with VRI controls.  During the 2012 growing season the VRI controls were used only to turn the sprinklers off when passing over non-cropped areas in the fields (drainage ditches, wet areas, wildlife corridors, etc.)  Eleven demonstration fields will be instrumented in 2013 and full precision irrigation will be implemented during the 2013 growing season.  This paper will describe our system in detail providing data from the components which have been completed and are operational.