<i>IrrigApp</i> : An Online Tool for Determining Crop Water Use and Evaluating Irrigation Scheduling Options

The rules governing irrigation scheduling in agriculture depend on local weather conditions. However, there is a lack of easy‐to‐use tools to facilitate accessing, compiling, analyzing, visualizing, and transforming local weather data into valuable information to help farmers make more accurate planning and day‐to‐day irrigation management decisions. Therefore, this study was aimed at developing a user‐friendly online tool to evaluate the impact of irrigation and other factors on daily and seasonal soil water, crop water use, and crop water stress based on local historical weather data for South Carolina, United States. An interactive online tool called IrrigApp was developed and deployed using Shiny R and the Shiny Server cloud hosting service (shinyapps.io). IrrigApp uses county‐specific historical grass‐reference evapotranspiration (ETo) and rainfall data (from 2000 to 2022) from the NC CRONOS/ECONet Database, together with several user‐selected inputs (i.e., county, crop, soil type, start date, end date, irrigation applications, and irrigation efficiency). IrrigApp calculates daily crop evapotranspiration (ETc) and conducts a daily soil water balance to estimate several daily and seasonal variables, such as ETc under dryland and irrigated conditions, soil water content in the crop root zone, and water losses by runoff and deep percolation. The single crop coefficient procedure and a simplified soil water balance equation, described in FAO‐56, were used to calculate daily ETc and soil water content for five summer row crops typically grown in South Carolina (i.e., cotton, corn, soybean, peanuts, and sorghum). Daily runoff was estimated following the Soil Conservation Service (SCS) runoff equation, and water that infiltrated exceeding the soil water holding capacity in the crop root zone was considered deep percolation. Two sample IrrigApp simulations were conducted to illustrate its functionality and outputs. The simulations were performed for cotton grown in Orangeburg County, South Carolina, for the 2020 growing season under dryland and irrigated conditions. The results showed that the simulated dryland crop suffered crop stress, which reduced seasonal ETc by 22%. However, the results of irrigated simulations showed that applying 6 in. (150 mm) of irrigation properly timed during three irrigation events could closely meet the crop water requirements and prevent significant water stress, resulting in an ETc reduction of only 3%. These results showed that IrrigApp provides an easy way to visualize how seasonal and daily changes in weather conditions affect soil water, crop water use, and crop stress. IrrigApp also facilitates visualizing the impact of timing and amount of irrigation applied on daily and seasonal ETc and water losses.