Advanced irrigation engineering: Precision and Precise

Authors: Howell, Terry; Evett, Steven - Steve; Oshaughnessy, Susan; Colaizzi, Paul; Gowda, Prasanna

Submitted to: Journal of Agricultural Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2011
Publication Date: 1/20/2012
Citation: Howell, T.A., Evett, S.R., O'Shaughnessy, S.A., Colaizzi, P.D., Gowda, P. 2012. Advanced irrigation engineering: Precision and Precise. Journal of Agricultural Science and Technology. 2(1A):1-9.

Interpretive Summary: This paper is a summary and review of irrigation advances in precision irrigation (PI) or site-specific irrigation (SSI). SSI/PI has been widely used in research; however commercialization of the systems has been slow. Typically SSI/PI is used where variability in soil texture that affects soil water holding capacity and crop yield are important. SSI/PI uses variable rate application technologies, mainly with center-pivots or lateral-move or linear irrigation machines, to irrigate specific management zones within a field by varying the application to match crop needs or soil water holding capacity. SSI/PI can avoid irrigating management zones with poor internal drainage; zones with poor crop growth or development (from fertility or salinity or other soil factors or even crop diseases); or zones with known problems (rock outcrops, physical obstructions, etc.). The variable rate applications are achieved by a range of engineering options from variable nozzle flow rates, pulsing nozzle flows, or multiple nozzles on separate submains to vary application rates. Newer center pivot and linear machines are usually controlled by on-board microprocessor systems that are can be integrated with supervisory control and data acquisition (SCADA) controllers for control and communication. Communication can be with radio telemetry, wireless internet links, or cellular telephones. Precision irrigation is of limited use without precise irrigation scheduling (temporally and spatially). Irrigation scheduling can be based on measured soil or plant water status. Recently, remote sensing methods have been used. Plant or soil sensors are most often utilized to start or complete an irrigation event based on specific criteria. Automated weather stations are now widely used to provide basic site information on the irrigation requirement using either crop development models or simpler reference evapotranspiration (ET) data to be used with crop coefficients (Kc).

Technical Abstract: Irrigation advances in precision irrigation (PI) or site-specific irrigation (SSI) have been considerable in research; however commercialization lags. A primary necessity for it is variability in soil texture that affects soil water holding capacity and crop yield. Basically, SSI/PI uses variable rate application technologies, mainly with center-pivots or lateral-move or linear irrigation machines, to irrigate prescription-specific management zones within a field by varying the application to match crop needs or soil water holding constraints. SSI/PI can avoid irrigating management zones with poor internal drainage; zones with poor crop growth or development (from fertility or salinity or other soil factors or even crop diseases); or zones with known problems (rock outcrops, physical obstructions, etc.). One limitation for SSI/PI is defining the objective function for the production goals/constraints. Examples of objective functions include optimizing overall field productivity, minimizing water use, or reducing environmental on-site or off-site impacts. The variable rate applications are achieved by a range of engineering options from variable nozzle flow rates, pulsing nozzle flows, or multiple nozzles on separate submains to vary application rates. Newer center pivot and linear machines are controlled by on-board microprocessor systems that are easily integrated with supervisory control and data acquisition (SCADA) controllers to integrate communication and variable rate application controls for specific sets of nozzles or individual nozzles for determined management zones. Communication for center pivot or linear controllers is typically done using radio telemetry, wireless internet links, or cellular telephones. Precision irrigation is of limited utility without precise irrigation scheduling (temporally and spatially). Irrigation scheduling has advanced considerably in the past 20-30 years with improved technology to measure soil or plant water status and, especially, within the past 10-15 years to utilize remote sensing tools. Plant or soil sensors are most often utilized to initiate or complete an irrigation event based on specific criteria. Automated weather stations are now widely used to provide basic site information on the irrigation requirement using either crop development models or simpler reference evapotranspiration (ET) data to be used with crop coefficients (Kc). Remote sensing is increasingly being utilized to measure crop water status (usually through crop surface temperature) or crop development or ground cover based on spectral reflectance from specific electromagnetic wave bands, but future satellites (i.e., Landsat 8) may not contain a thermal radiation band critical for crop stress and ET. Usually, the red band (0.63-0.69 micro-m or band 3 on Landsat TM or EM+) and the near infrared band (0.76-0.90 micro-m or band 4 on Landsat TM or EM+) are used to determine the Normalized Difference Vegetation Index (NDVI). Satellite and aircraft remote sensing platforms have not proven useful for irrigation scheduling due to issues of too coarse spatial and temporal resolutions and too long turn-around times for getting data processed and useful information to the field. Inexpensive infrared thermometers (IRTs) are being used as crop thermal temperature detectors ranging from hand-held to fixed units in the field to newer wireless IRTs using mesh networks to communicate with controllers. Near-surface remote sensing with sensors mounted on moving irrigation systems may provide critical spatial integration from point weather networks and useful feedback on crop ET and irrigation controls in advanced automated systems, particularly for SSI/PI.