Key Performance Indicators for Variable Rate Irrigation Implementation on Variable Soils

Abstract

Decision support tools for precise irrigation scheduling are required to improve the efficiency of irrigation water use globally. This paper presents a method for mapping soil variability and relating it to soil hydraulic properties so that soil management zones for variable rate irrigation can be defined. A soil water balance is used to schedule hypothetical irrigation events based on (i) one blanket application of water to eliminate plant stress, (uniform rate irrigation, URI) and compares this to (ii) variable rate irrigation (VRI), where irrigation is tailored to specific soil zone available water holding capacity (AWC) values. The key performance indicators: irrigation water use, drainage water loss, nitrogen leaching, energy use, irrigation water use efficiency (IWUE) and virtual water content are used to compare URI and VRI at three contrasting sites using four years climate data for a dairy pasture and maize crop and two years climate data for a potato crop. Our research found that VRI saved 9 - 19 % irrigation water, with accompanying energy saving. Loss of water by drainage was also reduced by 25 - 45% using VRI, during the period of irrigation, which reduced the risk of nitrogen leaching. Virtual water content of these three primary products further illustrates benefits of VRI and shows that virtual water content of potato production used least water per unit of dry matter production.