Monitoring Effective Container Capacity: A Method for Reducing Over-Irrigation in Container Production Systems

Abstract

A gravimetric substrate moisture monitoring system was used to control irrigation frequency and volume within a narrow range of substrate moisture contents to study the effects of reduced irrigation volume on growth and water use of baldcypress (Taxodium distichium L.). The four irrigation treatments were: control (daily scheduled irrigation at 16: 30 hours for 15 minutes or 6.75 liters (1.74 gal)/day) and 100, 80 and 60% of effective container capacity (ECC). Effective container capacity was defined as the maximum mass of a container, substrate and plant unit after gravitational water loss. Maintaining substrate moisture content at 80 and 60% ECC reduced baldcypress height, caliper, dry weight, and total plant N, P, and K content, but did not effect N, P or K concentrations compared to scheduled irrigation and 100% ECC treatments. Water use efficiencies (WUE, the volume of irrigation lost to evapo-transpiration divided by the total volume of irrigation applied) were determined for three dates. Plants under scheduled irrigation had WUEs of 17, 33, and 42% on July 8, July 24, and August 16, respectively. In contrast, WUE for plants under 100, 80 and 60% ECC treatments was 100% (no leachate) for the same dates. Plant water use under 80 and 60% ECC treatments was lower than that under scheduled and 100% ECC treatments. Plants under the 100% ECC treatment were 1.6 m (63 in) tall in August and used 2.6 liters (0.68 gal) of water per day. The gravimetric substrate monitoring system was an effective, plant-integrated method of reducing leachate volume that required minimal maintenance under the four month experimental period.