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Evaluation of sector control variable rate irrigation (VRI) on a production field
Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Green Z., Tagert M.L., Paz J., Lo T.

Mississippi's average annual precipitation is approximately 127 cm, of which 70% occurs in the winter and spring months outside of the growing season. Accordingly, an increasing number of on farm water storage (OFWS) systems have been built in northeast Mississippi in recent years. These systems capture and store off-season precipitation and runoff that can later be used for irrigation. With limited rainfall during the growing season, farmers solely dependent on surface water have a finite amount of water to use for irrigation through the growing season and therefore must irrigate efficiently. This study evaluates the costs and benefits of sector control variable rate irrigation (VRI) on an 18-hectare corn and soybean production field under sprinkler irrigation in Noxubee County. During the 2022 growing season, corn was planted on April 25 and harvested on August 20. Elevation, yield, and soil moisture data collected from 2018-2021 were analyzed in Esri's ArcMap software, and two irrigation management zones were created in the field. A soils layer was not included in this geospatial analysis because previous gridded soil sampling confirmed a homogeneous soil type of silty clay loam with small areas of silt loam. A 'dry' irrigation management zone was placed in the southern section of the field, and a 'wet' irrigation management zone was placed in the northwestern section of the field. Each management zone is approximately one quarter of the area under the center pivot. Each zone was then sub-divided into six different pie-shaped sectors. The three control sectors received 1.9 cm of water, which was the conventional amount of irrigation applied by the farmer. The other three test sectors received 1.5 cm of water, which was a 20% reduction from the conventional amount. The center pivot is equipped with a Linsdsay Growsmart IM3000 magnetic flow meter to measure water use. Two sets of Watermark 200SS granular matrix soil moisture sensors were placed in the centroid of each sector at depths of 30 and 61 cm to measure soil water tension throughout the growing season, and sensors were removed just before harvest. Yield data was recently obtained from the farmer, and soil tension data is currently being analyzed with yield data to determine if water savings were realized without a loss in yield. This presentation will include preliminary results from this multi-year study.

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