2017 ASHS Annual Conference

The Smartirrigation™ application (smartirrigationapps.org), is a tool designed to aid farmers in conserving water and nutrients for crops through the improvement of irrigation scheduling. Currently this application utilizes crop coefficients based on a days after planting (DAP) model to schedule irrigation. However, plant growth and development is more accurately determined by growing degree days (GDD) than DAP. Growing degree day models have been shown to more accurately predict the development of plant phenology in a season as the model attributes changes in crop development stages to accumulated heat units. Soil water tension data and water root zone deficit values were analyzed retroactively in order to compare expected plant water use based on the days after planting model and a growing degree day model. This study aimed to validate crop coefficients for watermelon and adjust them to reflect differences in DAP and GDD models. In 2016, the watermelon variety ‘Melody’ was planted into raised beds of black plastic mulch in Tifton, Georgia and irrigated based on historical evapotranspiration values, the Smartirrigation application, or soil moisture sensors (tensiometers). Soil moisture levels were measured using Watermark™ sensors at depths of 15, 25, and 35 cm. Plots were arranged in a randomized complete block design with four replicates. An on-site weather station was used to calculate GDD. This trial was used to validate and adjust the crop coefficient curve used by the Smartirrigation™ application, and to assess the efficacy of using a DAP model to determine crop coefficients of plasticulture-grown watermelon.