Optimising a sensor-based irrigation protocol for a large-scale cut-flower operation in southern California

J.D. Lea-Cox, J. Williams, M.A. Mellano
A network of wireless cellular nodes (EM50G, Meter-Group, Inc., Pullman, USA) and sensors have been deployed at Mellano and Company in Oceanside, CA, to provide managers with soil moisture (volumetric water content, VWC) and electrical conductivity (EC) data, to aid in day-to-day irrigation and salinity management decisions. The primary objective was to achieve a mandated 25% cut in water use without affecting the yield or quality of various cut-flower crops, many of which are grown in long-lived (4-7 year) perennial blocks. Data from 15 nodes/sensors in eight different crops and fields are logged every 15 min from GS1 (VWC) and GS3 (EC) sensors and transmitted by EM50G nodes to a cloud server, up to six times day-1. All data are integrated into a graphical database program (SensorwebTM, Mayim, LLC), which is accessible to anyone with an internet connection and access to the password protected website for the company. To rationalize the information that the growers receive, a standardized installation protocol was implemented. Firstly, a combination of VWC and EC sensors are placed at two depths (typically 15 and 30 cm) in the crop rooting zone (influenced by crop development and longevity), to quantify how soil moisture is influenced by daily crop water use. The intent is to actively manage irrigations without significant leaching, except when salts become excessive. Secondly, the specific field capacity (FC) for each field is derived from in situ data, to provide the upper threshold for irrigation, to avoid excessive irrigation durations. A specific threshold VWC for irrigating each crop and soil type is calculated (typically 20% of FC), to provide irrigation managers with a measure of readily-available water. Threshold soil VWC alerts for each block are then created in SensorwebTM; the system texts/emails the irrigation manager when that set-point VWC is reached. In this manner, growers are able to fine tune irrigation frequency and duration events (to not exceed FC and increase leaching), to match daily plant water use and crop development over the season. Water savings of about 40% were achieved with Solidago in 2015, and 50-60% for myrtle through the fall/winter of 2015. In this way, Mellano and Company has been able to achieve their targeted irrigation reductions, without compromising crop yield or quality.
Lea-Cox, J.D., Williams, J. and Mellano, M.A. (2018). Optimising a sensor-based irrigation protocol for a large-scale cut-flower operation in southern California. Acta Hortic. 1197, 219-225
DOI: 10.17660/ActaHortic.2018.1197.29
Myrtus, myrtle, Solidago, goldenrod, EM50G, wireless datalogging, large-scale, soil volumetric water content, electrical conductivity, irrigation scheduling

Acta Horticulturae