Towards Variable Rate Irrigation in Kentucky (Year 1)
Sustainable Production
SustainabilityWater resistanceWater supply
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Ole Wendroth, University of Kentucky
Co-Principal Investigators:
Project Code:
Contributing Organization (Checkoff):
Institution Funded:
Brief Project Summary:
Pivot irrigation is not new to soybean production. However, using variable rate irrigation (VRI) to apply different amounts of water to specific areas of soybean fields is a newer practice that hasn’t caught on yet in Kentucky. Ole Wendroth, professor in the Department of Plant and Soil Sciences at the University of Kentucky, has been researching using different irrigation rates on different soil zones within soybean fields, through research projects funded from the Kentucky Soybean Board. Kentucky soils are extremely spatially variable because of karst topography and erosion events in the past before no-till was introduced.
Key Beneficiaries:
#agronomists, #hydrologists, #soil scientists, #Soybean producers, #water engineers
Unique Keywords:
# water use efficiency, #environmental , #irrigation, #pivot irrigation, #soil zones , #spatial soil variability, #variable-rate irrigation
Information And Results
Project Summary

Kentucky farm soils are known for their spatial variability that is typical for the Karst landscapes and caused by soil erosion processes leaving the land surface with a heterogeneous mosaic of infiltration capacity. Most irrigation systems in Kentucky and in the Southeastern U.S. are pivot systems that allow a spatially uniform rate of water supply. This technical limitation leads to either optimum water application, over- or under-application of water. The latter two imply not only economic losses for the farmer but also environmental harm through sub-optimal use of resources or even loss of resources through surface runoff or leaching. Little is known yet how to design an irrigation map and how to manage irrigation on the go while considering local soil properties, crop growth stage, past management, weather forecast, and technical precision of VRI system. In this project, the technicalities of variable-rate irrigation will be explored and used to compose a manual with guidance for growers on the various steps of a sound variable rate irrigation management.

Project Objectives

The objective of this project is to develop a protocol that includes:
- processing of site-specific soil information,
- crop growth development through different types of remote sensing,
- database management,
- access to precise local weather information, and
- knowing the sensitivity of the irrigation system and its limitations.

Project Deliverables

- Evaluation of the efficiency of VRI over uniform rate,
- Manual with guidance on VRI for growers.

Progress Of Work

Final Project Results

One way of securing high soybean yields in a sustainable way is to irrigate. This strategy is especially relevant four double crop soybeans that are planted after wheat harvest when the soil water storage is depleted to some extend by the wheat. To meet the plant's water needs irrigation water has to be applied efficiently. For this study, a center pivot system was used that was recently upgraded to a variable-rate irrigation (VRI) system was tested for the first time in combination with a new soil water content measurement system. One objective was to validate the application of two different irrigation rates. The second objective was to identify soil water content increase in the soil profile during a rainfall or irrigation event, and to evaluate the agreement between soil water content change and amount of precipitated or irrigated water. Third, the Root Zone Water Quality Model 2 (RZWQM2) which is an agro-ecosystem model that can simulate plant growth and soil processes was used to simulate profile soil water dynamics and crop growth. Two spatially different irrigation rates of 0.5 and 0.25 inches were used in eight different zones in a farmer’s field at Hillview Farms, Princeton, Caldwell County, Kentucky. The eight zones were located in two different soil types within the same field, i.e., silt loam and silty clay. The irrigated amount that was caught in a tipping bucket rain gauge was slightly below the intended amount. After calibration, the simulation model was able to describe soil water content time series in different soil layers. Accuracy of the model is comparable to the results obtained in other studies in the literature. For the silty clay soil, 0.5 inches of irrigation increased yield by approximately 7 bu/ac whereas for the silt loam soil, the lower irrigation rate did not cause a yield decrease. In drier years, this result would be expected top differ.

Benefit To Soybean Farmers

Through the findings of this research project and the manual that explains the technical steps of variable rate irrigation (VRI), growers are enabled to improve crop water use efficiency, and avoid negative environmental impact of over-irrigation. Both result benefits in economic return of irrigated soybean production.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.