Potential water conservation using site-specific variable rate irrigation

Authors: Stone, Kenneth - Ken; Bauer, Philip; Sigua, Gilbert

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2019
Publication Date: 6/19/2019
Citation: Stone, K.C., Bauer, P.J., Sigua, G.C. 2019. Potential water conservation using site-specific variable rate irrigation. Applied Engineering in Agriculture. 35(6):881-888. https://doi.org/10.13031/aea.13108.
DOI: https://doi.org/10.13031/aea.13108

Interpretive Summary: Site-specific variable-rate irrigation systems can spatially manage irrigation within sub-field-sized zones and optimize spatial water use efficiency. The goal of the research is to provide farmers and consultants a tool to evaluate the potential benefits of implementing variable rate irrigation. In this research, we evaluated the potential water savings using variable rate irrigation management compared to uniform irrigation management. A 21-year simulation study was carried out on a field with varying degrees of soil variability. In our simulations, we maintained soil moisture greater than 50% of the soils’ water holding capacity in the top 30 centimeter (cm) of the soil rooting zone using two irrigation scenarios: 1) a standard 12.5 millimeter (mm) irrigation per application; and 2) an application to refill the soils’ water holding capacity. The simulated field had 12 soil mapping units with soil water holding capacities in the surface 30-cm ranging from 42 to 70 mm. The 21-year simulation covering all weather conditions for each soil produced 2 significantly different irrigation management zones for scenario 1 and for scenario 2 only 1 management zone. However, when the 21-year period was sub-divided into periods with low, intermediate, and high seasonal rainfall totals, the simulations identified 1 to 5 potential management zones. Simulated irrigation application depths between specific management zones ranged from 17 and 38 mm. However, when the actual soil areas of the study field were utilized to calculate the total volume of irrigation water applied, variable rate irrigation required from 0.5% less water to 6.8% more water than uniform irrigation. These results indicate that variable rate irrigation system design and management should not be solely based on long term average weather conditions. Using years with differing weather conditions should be used for potentially identifying management zones for variable rate irrigation systems.

Technical Abstract: Site-specific variable-rate irrigation (VRI) systems can spatially manage irrigation within sub-field-sized zones and optimize spatial water use efficiency. The goal of the research is to provide farmers and consultants a tool to evaluate the potential benefits of implementing VRI. The specific objective of this research is to evaluate the potential water savings using VRI management to uniform irrigation management to maintain soil water holding capacity above 50% depletion using two irrigation scenarios: 1) a standard 12.5 millimeter (mm) irrigation per application; and 2) an application to refill the soil profile to field capacity. A 21-year simulation study was carried out on a selected field with varying degrees of soil and topographic variability. The simulated field had 12 soil mapping units with water holding capacities in the surface 30-centimeter (cm) ranging from 42 to 70 mm. The 21-year simulation covering all weather conditions for each soil produced only 2 significantly different irrigation management zones for scenario 1 and for scenario 2 only 1 management zone. However, when the 21-year period was divided into periods with different ratios of rainfall to potential evapotranspiration, the simulations identified 1 to 5 management zones with significantly different irrigation requirements. These results indicate that variable rate irrigation system design and management should not be solely based on long term average weather conditions. Using years with differing weather conditions should be used for potentially identifying management zones for VRI systems. Managing irrigation using multiple management zones differed in irrigation application depths between specific management zones ranged from 17 and 38 mm. However, when the actual soil areas of the study field were utilized to calculate the total volume of irrigation water applied, it resulted in an increase in water usage in the 2 and 4 management zones ranging from -1.2 to 5.8%. Water usage with VRI over uniform irrigation was greater by -1.6 to 6.8% in the 12.5 irrigations and by -1.2 to 2.2% for the field capacity irrigations.