Irrigation Based on Plant Daily Water Use Conserves Water without Affecting Plant Growth, Poster Board #220

Container-grown woody ornamentals were irrigated with 4 treatments based on daily water use (DWU) to study the impact of irrigation regime on plant growth, leachate electrical conductivity and pH, and runoff water volume and nutrient content. Hibiscus syriacus ‘Bricotts’, Euonymus alatus ‘Select’, Weigela  florida ‘Alexandra’, and Spiraea japonica ‘Yan’ were grown in 10.2-L (#3) containers and subject to four overhead irrigation treatments: 1) irrigation scheduled to replace 100% DWU per application (100DWU); 2) irrigation alternating every other application with 100% replacement of DWU and 75% DWU the following application (100-75); 3) irrigation scheduled on a three-application cycle replacing 100% DWU followed by two applications replacing 75% DWU (100-75-75); and 4) irrigation scheduled on a four-application cycle replacing 100% DWU followed by three application replacing 75% DWU (100-75-75-75). Container substrate consisted of 85% pine bark: 15% peatmoss (vol: vol). Plants were fertilized on 5 July 2011 with 26 g per container of a 17.0N-3.5P-6.6K control released fertilizer with micronutrients with a nutrient release period at 27 °C of 4 months (Harrell’s, Inc., Lakeland, FL). The substrate moisture content was determined by 10 HS soil moisture sensor (Decagon Devices, Inc., Pullman, WA 99163). Plant DWU was calculated as moisture content after irrigation minus moisture content before irrigation the following day. The irrigation amounts were scheduled by a programmed data logger (CR3000, Campbell Scientific Inc., Logan, UT) based on the highest DWU reading from the sensors in each zone. Irrigation applications were separated by at least 24 hrs. The average daily irrigation amount applied for 100-75, 100-75-75, and 100-75-75-75 were 424 mL, 473 mL, and 423 mL, respectively, and less than 513 mL in 100DWU. There were no differences in final plant growth, electrical conductivity, or runoff nutrient content between treatments, and only a small difference in pH between treatments. These results suggest that irrigation water could be reduced without affecting plant growth.