Feasibility of using pyranometers for continuous estimation of ground cover fraction in table grape vineyards

Antonio Martinez-Cob,Olga Blanco,Eva T Medina,Kosana Suvočarev,Jose M Faci

doi:10.5424/sjar/2014123-5453

Antonio Martinez-Cob, Olga Blanco + Show 3 more

Open Access

https://doi.org/10.5424/sjar/2014123-5453

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Abstract

This paper evaluates the feasibility of using pyranometers for continuous estimation of ground cover fraction (GCF) at remote, unattended sites. Photographical techniques were used for measuring GCF (GCFref) at a table grape vineyard grown under a net. Daily pyranometer-driven GCF estimates (GCFpyr) were obtained from solar radiation measurements above and below the canopy. For GCFpyr computation, solar radiation was averaged for two hours around solar noon (midday periods) and for daylight periods (8:00 to 18:00 Universal Time Coordinated). GCFpyr and GCFref (daylight periods) showed a good agreement: mean estimation error, 0.000; root mean square error, 0.113; index of agreement, 0.967. The high GCF attained, the large measurement range for GCF and the presence of the net above the table grape were the likely reasons for the good performance of GCFpyr in this crop despite the short number of pyranometers used. Further research is required to develop more appropriate calibration equations of GCFpyr and for a more detailed evaluation of using a short number of pyranometers to estimate GCF.

Highlights

Several biophysical parameters exist to characterize plant growth
This paper evaluates the feasibility of using pyranometers for continuous estimation of ground cover fraction (GCF) at remote, unattended sites
For GCFpyr computation, solar radiation was averaged for two hours around solar noon and for daylight periods (8:00 to 18:00 Universal Time Coordinated)

Summary

Introduction

Several biophysical parameters exist to characterize plant growth. For the aerial part, the most commonly used are: 1) leaf area index (LAI), i.e. the one-sided green leaf area per unit ground surface area; 2) fraction of absorbed photosynthetically active radiation (fPAR) known as midday canopy light interception fraction, i.e. the ratio of ground measured PAR to full sun PAR subtracted from 1; and 3) ground cover fraction (GCF), i.e. the fraction of the ground covered or shaded by the crop canopy near solar noon as observed from directly overhead (Allen et al, 1998; Williams & Ayars, 2005; Allen & Pereira, 2009). The fPAR and the GCF can be considered as practically identical (Ayars et al, 2003). GCF (and fPAR) is well related to such paramount meteorological variable as global solar radiation. GCF is directly related to several plant characteristics such as the canopy size and the proportion of solar radiation captured by plants for potential conversion into evapotranspiration (Allen et al, 1998; Williams & Ayars, 2005). GCF has been used as an auxiliary variable in the estimation of water

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