Location: Soil and Water Management ResearchTitle: Variable rate irrigation (VRI) Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/20/2016
Publication Date: 1/19/2016
Citation: Evett, S.R., Oshaughnessy, S.A., Andrade, A., Schwartz, R.C. 2016. Variable rate irrigation (VRI). 2016 irrigated crop production update, Lethbridge, Canada.
Technical Abstract: Variable rate irrigation (VRI) technology is now offered by all major manufacturers of moving irrigation systems, mostly on center pivot irrigation systems. Variable irrigation depths may be controlled by sector only, in which case only the speed of the irrigation lateral is regulated. Or, variable depths may be applied both by sector and radial distance from the pivot point, in which case both the lateral rate of movement and the flow rate from individual nozzles or banks of nozzles are regulated. More complex management zones can be addressed using both lateral speed and radial zone control, but sector-only control can be useful in some situations. Wind speed and direction can influence the applied depth achieved within a management zone, but the influence of wind is reduced over multiple irrigations such that clear and controlled differences between management zones can be achieved. The management plan for VRI can be described by a prescription map showing the variable irrigation depths desired in each control zone. A digital representation of the prescription map is uploaded to the center pivot control panel to guide irrigation. Obvious uses of VRI include avoiding irrigation on non-productive features within a center pivot field such as rock outcroppings, roads, waterways, ponds and unfarmed areas. In these cases, a static prescription map may be determined once and applied throughout the irrigation season. Some less obvious uses involve varying irrigation application depths in order to address time varying spatial differences in crop response due to soil texture, depth and restricting layers, slope, aspect, saline seeps or other salinity problems, and disease and pest infestations. In cases of spatially variable soil texture and depth, bulk electrical conductivity mapping may be used to improve NRCS soil maps to more accurately reflect spatial patterns and guide a prescription map that may be static, but that likely will require updating during the season. Indeed, most of the less obvious uses of VRI require dynamic prescription map determination, and this can be accomplished through combined plant and soil stress monitoring if spatial coverage is sufficient. Scientists at the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, have patented an Irrigation Scheduling Supervisory Control and Data Acquisition (ISSCADA) system, and have commercialized a patented soil water sensor and a wireless infrared thermometer (IRT) that are used in the ISSCADA system on a center pivot irrigation system to sense and provide maps of crop water stress. The system then converts these spatial data to prescription maps for acceptance by the irrigation manager. The ISSCADA system is embodied in a client-server software system for managing multiple center pivot irrigation systems. The system has been successfully applied to corn (conventional and drought tolerant), cotton, sorghum (short and long season), soybean and winter wheat, with yields and water use efficiencies routinely as good, and often better than, those achieved using scientific irrigation scheduling based on weekly soil water content readings made using a field-calibrated neutron probe.