Journal of NACAA

Determining Irrigation Scheduling for Vegetable Crops Using the Blue Dye Test

ISSN 2158-9429

Volume 13, Issue 1 - June 2020

Editor: Bindu Poudel-Ward

Abstract

Sandy and loamy sand soils have low water holding capacities and require frequent irrigation events to potentiate yield. Proper scheduling of irrigation events in vegetable fields, with drip irrigation, can be simply identified using a blue-dye indicator, which is injected to color the soil. The objective of this educational demonstration project was to assist and educate growers, in the scheduling of irrigation events, using the blue dye test method. Conducted in a 42-acre field located in Brooks County, GA, the blue-dye test evaluated six treatments representing irrigation timings at 15, 20, 25, 30, 40, and 60 minutes. Irrigation was applied at 500 gpm and 60 psi, while blue-dye indicator was injected after system pressurization. Treatments were replicated 4 times in a complete randomize design. Replications were considered a bed 100-ft. long. After irrigation, trenches were open along the soil profile and measurements of the wet zone were made. Soil measurements recorded the depth between bed surface and deepest dye observation, maximum wetted width located in wet zone, and greatest distance between sides of wetted zone below an emitter. Downward soil water movement linearly increased with irrigation timing. After 40 and 60 minutes of irrigation, blue-dye indicator was measured at 12.5-in and 15-in of soil depth, respectively. This indicates water was moving below bell pepper root zone (12-in of soil depth), under 60 minutes of irrigation. Bell pepper plants are typically planted in double-rows 9 inches from the drip line. Lateral soil water movement had a plateau at 9.5 inches from the drip line with 40 minutes of irrigation. Therefore, irrigation events exceeding 40 minutes only represented downward water movement. Seeking to optimize irrigation scheduling, growers can reduce row-spacing from the drip line to 8 inches. The success of a blue-dye test is visual and can be easily conducted by extension agents.