Variability of wind conditions in citrus groves compared with those recorded outside

Abstract

Wind velocity and direction, which are normally reported at certain time intervals, fluctuate substantially within a short time frame.  These fluctuations may have a significant effect on spray deposition of air-assisted sprayers used in citrus production.  Wind measurements are usually made inside or outside a grove at about 10 m height but the latter may not accurately represent the wind conditions within the grove.  The objective of this study was to compare data recorded by the Florida Automated Weather Network (FAWN) outside the grove at 10.0 m above the ground with the measurements made within a citrus grove at different heights.  Within the grove, wind velocity and direction data were collected at 10.0, 3.6, 3.0, 2.4, 1.8, 1.2, and 0.6 m above the ground at 1-s interval.  For the same period, FAWN data were available at a minimum of 15-min interval.  Results of the 10-m height measurements showed good correlation between wind conditions recorded outside grove and those collected within the grove (r = 0.69 and 0.94 for wind velocity and direction, respectively).  However, average wind velocity and direction at both sites were significantly different (p = 0.05).  Within the grove, wind velocities of 1.5 m/s or less, recorded at 10 m height, showed almost zero wind velocity at lower heights.  Within the grove, maximum wind velocities recorded at 3.6 – 0.6 m amounted to only 59% – 20% of wind velocity recorded at 10 m, respectively.  Averaging wind velocity over 15-min interval reduced the wind variability of 1‑s interval by 90%.  For field characteristics similar to those described in this study, wind conditions recorded at 10 m height outside grove cannot reliably represent wind conditions inside grove, particularly within the canopy height.

Keywords: FAWN, spraying conditions, wind direction, wind measurement site, wind sensor, wind velocity