Electro-leaf, a biomimicry system to estimate in-canopy airflow in fruit crops

Highlights

• We develop a system to estimate airflow in-canopy.

• The sensor mimics a real leaf which oscillates randomly under the air turbulence.

• Results show differences in airflow as a function of the air speed.

• Results show differences in airflow as a function of the canopy size.

Abstract

This paper proposes a method, based on an array of sensors, to estimate in-canopy airflow in fruit orchards and vineyards. These sensors, called electro-leaves, mimic a real leaf which oscillates randomly under the air turbulence coming from an air-assisted sprayer. These oscillations are sampled at 700 Hz and processed in order to detect peaks of movement. The value of these peaks could be used as a reference to make adjustments to the operating parameters of the sprayer, with the aim of improving spray deposition and reducing drift. Results show that the electro-leaves estimate different airflows as a function of the air volume, the tractor forward speed and the canopy sizes. Also, the detected airflow is highly correlated with the wind speed measured by an ultrasonic and a vane anemometer.

Introduction

In fluid dynamics, turbulence is a flow regime characterized by chaotic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time (Davidson, 2004). When vines or fruit trees are treated using powerful air-assist sprayers, air turbulence is generated inside the canopy. This air is extremely important because it transports spray droplets (water and chemical solution) from the sprayer to the canopy center (Balsari et al., 2001). Also, the air speed and volume need to be adjustable according to the growth stage of the vine canopy (Balsari et al., 2001, Balsari et al., 2005, Pergher and Gubiani, 1995, Pergher, 2005). Balsari et al. (2008) showed that the use of low air velocities, around 5 m s⁻¹, enabled higher spray deposition on the leaves and better evenness of distribution within the vine canopy.

The desired air and liquid application technique is to match the spray plume with the canopy; too little air results in poor penetration, too much air results in spray drift and reduced deposition (Cross et al., 2003, Landers, 2010). Airflow (direction, speed, and volume) is an important aspect when applying spray to tree and vine crops. Measuring airflow outside a three-dimensional crop is relatively straightforward using a variety of wind anemometers (cup, hot-wire, vane, sonic, acoustic, laser) but measuring airflow within the canopy is more difficult, frequently impossible and time-consuming with such devices. Air turbulence is now recognized as more important with the narrower canopies and row widths found in modern vineyards and orchards (Matthews, 1999). Melese et al., 2009, Melese et al., 2010, used computational fluid dynamics to model the in-canopy airflow and droplet deposition, afterwards, they compared the results with field trials, where the wind speed was sensed using an ultrasonic anemometer at 6 m height above the ground. Lee et al. (2010), used a laser system to estimate the wind velocity reduction through trees. They correlated the canopy geometric characteristics (detected by the laser system) with the wind reduction, measured by a set of digital vane anemometers, situated in both sides of the tree.

In an effort to develop a simple airflow sensor for in-canopy use, the authors reviewed the scientific literature and found no such device exists in agricultural situations; a novel approach was required. The main objective of this research was to devise a simple, reliable indicator of airflow in the center of a fruit canopy. The novel device should be easily mounted on a mast and placed into the canopy by fruit grower or researcher.