The goal of precision irrigation is to improve productivity and sustainability by addressing spatial as well as temporal variability of soil and crop water status. Precision irrigation has its roots in variable rate irrigation (VRI) technology developed for center-pivot irrigation systems by the UGA precision agriculture team in 2001. The UGA team recognized that variable rate application of irrigation water was a key enabling technology for adoption of precision agriculture because fields in this region are highly variable in soil type and texture, moisture-holding capacity and slope.
Ignoring site-specific water needs while attempting to vary other inputs like fertilizers will prevent realization of the full potential of precision agriculture. VRI allows center pivots to vary water application rates along the length of the pivot by using electronic controls to cycle sprinklers and control pivot speed. Sprinklers are controlled individually or together typically in groups of two to 10, depending on the level of resolution desired by the farmer.
A 50% application rate (half the normal rate) is achieved by cycling the sprinklers on and off every 30 seconds. A 150% application rate is achieved by leaving the sprinklers on continuously while decreasing the travel speed of the pivot. If other grids along the length of the pivot require lower application rates, the VRI controller adjusts the sprinkler cycling pattern within those grids accordingly. VRI can be installed retroactively on most existing pivots. Application rates are determined from an application or prescription map.