Simulation of oil productivity and quality of N–S oriented olive hedgerow orchards in response to structure and interception of radiation
Highlights
► Analyses radiation-limited yield of olive hedgerow orchards of various structures. ► Identifies critical relationships between row height and alley width. ► Investigates impact of sloping canopy walls on orchard yield and oil quality. ► Provides guidelines for orchard design and management for high yield.
Introduction
Mechanized hedgerows are a new production method for olive and currently exist in two forms resulting from commercial innovation. First, in some vigorous high density (HD) orchards, first planted in 1980s at densities of 250–500 ha−1 in rows 6–8 m apart, where rows formed continuous hedgerows. Large overhead continuous harvesters were built to improve harvesting efficiency. Second, starting in 1995, super-high density orchards (SHD) were planted at densities of 1500–2000 ha−1 in rows 3–4 m apart to take advantage of availability and relative cheapness of smaller modified grape harvesters. Trees were trained to vase structures in HD orchards but are trained to central leader in SHD. Large harvesters can harvest rows to 4.5 m high and 4 m wide, while small harvesters are suited to hedgerows to 2.5 m high and 2 m wide.
Advantages of hedgerow designs are early yield and economy of mechanized management, especially harvesting, but also pruning. Disadvantages are high cost of establishing high-density plantations and associated training requirements of young trees, few suitable cultivars, vigour control in some conditions, and cost of mechanized harvesters. Freixa et al. (2011) present a recent comparative economic analysis of oil production by mechanized HD and SHD orchards in Spain.
In traditional olive production (10 m × 10 m), with trees trained to vase structure and heavily pruned to reduce water use, light distribution in tree canopies was not a limitation to growth or reproductive development (Mariscal et al., 2000, Villalobos et al., 2006). Consequently it was little studied (Tombesi and Cartechini, 1986, Tombesi and Standardi, 1977) until dense systems, mostly in hedgerow form, were introduced. Now there is quantitative information on the role of light in determination of fruit density, size and oil content in hedgerow orchards (Cherbiy-Hoffmann et al., 2012, Connor et al., 2012) and more recently on oil quality (Gómez-del-Campo and García, 2012). High light intensity promotes dense, large fruits with high oil percentage. Oil is also more stable against oxidation by virtue of high concentrations of polyphenols. Palmitic acid content is also higher, while oleic acid content is smaller than in fruits that develop in shade (Gómez-del-Campo and García, 2012).
For individual producers of hedgerow olives, the choice of a mechanized production system must be an appropriate combination of harvester and orchard design suited to location and resources. At present that places choice at either end of the HD-SD range, but mid-sized harvesters are becoming available so a wider range of orchard design will soon be possible. To date, most experiments on orchard design have been made at commercial scales and are slow and expensive, so other methods are required to investigate the performance of alternative designs across the range of feasible hedgerow structures.
This paper presents a simulation study of impact of canopy depth, width, and shape and row spacing on productivity of N–S hedgerow orchards. It uses a model of illumination of hedgerow orchards (Connor, 2006) and associated data on yield (Connor et al., 2012) and oil quality (Gómez-del-Campo and García, 2012) collected from a range of SHD orchards of cv. Arbequina in Spain. The analysis combines these components to simulate yield and oil quality across a wide range of structures, including many not yet tested experimentally or commercially. The approach provides guidance on hedgerow design, identifies issues that require resolution, and provides a framework for future research and development.
Section snippets
Terminology
Hedgerow orchards comprise rows of given spacing (r), height (h), canopy width at base (w), and slope to vertical (s) as depicted in Fig. 1. Alley width (a), for access and illumination, is the difference between row spacing and canopy width (r − w). Canopy depth (d) is less than row height (h) because bases of rows (t) are maintained free of vegetation to facilitate passage of harvesting and pruning machinery and, as needed, application of pesticides to trees and herbicides to inter-row
Row yield as a function of canopy depth and row spacing
Analysis of yield per unit row length of 1-m wide rectangular hedgerows in response to canopy depth (2–5 m) and row spacing (2–10 m) at 35°N is presented in Fig. 2.
The responses reveal how yield per unit row length increases rapidly with row spacing until alley width (row spacing − row width) equals canopy depth. Yield per unit row then increases more slowly with benefit from additional diffuse radiation entering alleys, not by more direct radiation. An important corollary is that at fixed row
Discussion
The conclusion that productivity of hedgerows depends upon row structure such that it establishes a strong relationship with the ratio of canopy depth to alley spacing is not new. Cain (1972) introduced the concept with his analysis of productivity of apple orchards and Smart and Robinson (1991) have used the same conclusion to propose optimal structures for vineyards. Many other studies have reported analyses of irradiance profiles in hedgerow orchards of various crops (Annandale et al., 2004,
Conclusions
Oil yield and quality respond, via responses to incident radiation, to structure in N–S oriented hedgerow olive orchards. Optimum row spacing for rectangular hedgerows occurs when canopy depth equals alley width, the difference between row spacing and canopy width. Narrow hedgerows provide greatest yields because at optimum spacing they allow most row length per hectare. Rhomboidal canopies, respond to improved irradiance patterns with greater yields mainly in wider canopies, in part achieved
Acknowledgements
The authors thank Jacinto Cabetas from El Carpio de Tajo, Antonio Capitán from Écija, Todolivo from Pedro Abad, and Agrícola La Veguilla from Puebla de Montalbán for access to olive orchards where this research was conducted. We also thank Ana Centeno, Angela Rodríguez, Beatriz Somoza, Enrique Vivas, Ignacio SanJuan, Felipe Oliva and Mercedes Ortí for helping in olive collection and oil extraction, and José Mª García for oil analysis. Thanks are also due to Peter Searles and Cecilia Rousseaux
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