Determining plant available water to practically implement deficit irrigation strategies in strawberry production

A field experiment was conducted at the University of Maryland Wye Research and Education Center from 2014-2016 to study deficit irrigation (DI) in strawberry (Fragaria x ananassa) production. A wireless sensor network consisting of nR5-DC control nodes (Meter-Group, Inc., Pullman, USA) independently irrigated replicate plots, based on soil volumetric water content (VWC) measurements. Soil water retention curves for the study site were developed using a Hyprop apparatus (UMS, Munchen, Germany); soil matric potential (SMP) was determined for a control (-30 kPa) and three DI treatments (-40, -50 and -60 kPa). Corresponding VWC values for the SMP were then determined by fitting the Mualem-van Genuchten (1980) model to the soil moisture retention data. These VWC values (36.7, 33.5, 32.1 and 30.2%, respectively) were used as threshold values/set-points in Sensorweb (TM) software (Mayim, LLC., Pittsburgh, USA). Irrigation events were triggered when the average VWC from duplicate 10HS soil moisture sensors (Meter-Group, Inc.) placed in the root-zone of plants in each plot was lower than the corresponding threshold value. In situ field SMP data for each treatment were measured using MPS-6 matric potential sensors (Meter-Group, Inc.) in each plot. Daily irrigation application volumes for each plot were also measured using flow meters (Badger Meters, Milwaukee, USA). Significant decreases in irrigation volumes were observed for the DI treatments, together with decreased fruit numbers and yield, indicating the sensitivity of strawberry plants to relatively small changes in plant available water (PAW) within the narrow SMP range imposed in the study. The study was repeated during 20152016, with T8 field tensiometers (UMS) incorporated to further validate soil moisture and SMP measurements and more accurately quantify PAW for the control and DI treatments. The control and deficit irrigation treatments imposed the desired soil matric potentials in the experiment. Differences in yield, number of fruit plant(-1), average fruit mass, and irrigation water productivity, however, were not significantly different.