262 Standard Time Domain Reflectometry Curves for Cyclic Irrigation Management in Container Production

Abstract

The physical properties of soilless substrates used in the nursery industry vary widely throughout the US, and, as such, present problems for accurate irrigation water management. Water management in soilless substrates is also a key factor in reducing the loss of soluble nitrogen and phosphorus from the root volume. Automated irrigation control that maintains the substrate water content above levels of plant water stress, yet below the maximum water holding capacity of the substrate will serve several positive roles: water and nutrients will be conserved, and losses from run-off minimized. We investigated whether Time Domain Reflectrometry (TDR) moisture sensors can be effectively calibrated for a range of horticultural substrates in various container sizes. A series of water desorption curves and TDR wave-traces (n = 10) were simultaneously derived for six soilless substrate source materials (pine bark, hardwood bark, promix, perlite, rockwool and a sieved sand control), using a modified tension table with four column heights (7-, 15-, 20-, and 25-cm equating to rockwool, #1, #3, and #5 pot sizes). Modifying the tension table allowed for the replication of individual columns (n = 10) of each substrate. The volumetric water desorbed at increasing desorption (positive air) pressures from 0 through 100 KPa was collected for each treatment. Repeated measurements with this apparatus allowed us to plot standard TDR curves for each substrate that can be used to accurately schedule cyclic irrigations. Implementing automated cyclic irrigation strategies in container production will allow for better monitoring and control of irrigation applications, and help conserve water and nutrients in the nursery.