Olives have been grown in California since the late 1700s. California is the sole commercial source of olives domestically, currently depending on about 1200 growers in the Central Valley (Sacramento and San Joaquin valleys) with biennial production of 115,500 tons (olive is strongly alternate-bearing). The average U.S. table olive production from 2001 to 2006 accounted for only 5.1% of total world production; the United States is the largest importer of olives at 125,000 tons (International Olive Council, 2007). ‘Manzanillo’ and ‘Sevillano’ are the most important domestic cultivars, contributing 76% and 20%, respectively, of U.S. production (U.S. Department of Agriculture, 2006). Hand harvesting is the main production cost, accounting for 65% of the gross return per ton in 2005 (Hester, 2006). Unlike other producers outside the United States, California's table olives are primarily processed as “black-ripe canned,” with only 5% processed by other methods. Despite the processed nature of the product, quality of the fresh fruit is the most important factor in developing mechanical harvesting in olives destined for table consumption (Ferguson, 2006).
Mechanical harvesting methods for olives destined for oil have been developed over more than 40 years, focusing on trunk shakers with detached fruit cast over the ground, canvas, or a catch frame. These harvesters maximize harvesting efficiency (Fridley et al., 1971; Pellenc, 1993); fruit quality is secondary. However, trunk shaker-type harvesters are impractical for table olives due to different tree structures and conditions, as well as the harvest maturity of the fruit (black-ripe for oil olives and green-immature for table olives). Trees are well-irrigated at harvest for table olives; thus, “barking” of the trunks can be problematic (Castro-García et al., 2007). Trees producing table olives are often tall, weeping, and old, with fluted, multiple trunks, making trunk attachment difficult or impossible and requiring greater energy input for shaking tall trees (Horvath and Sitkei, 2001). Furthermore, the detachment force required to remove unripe, small olives, averaging 3 to 6 g each, from pendulous willowy shoots is generally excessive (Kouraba et al., 2004). Fresh green olives are extremely susceptible to mechanical damage. Industrial processing for black table olives can mitigate some damage, but severe bruising, cuts, and abrasions are unacceptable to the consumer.
Some fruit crops, such as citrus (Citrus spp.) or blackberry (Rubus subgenus Rubus) can use canopy harvesters for harvesting processed or fresh market fruit (Peterson, 1998; Takeda and Peterson, 1999). Similar canopy harvesters may prove amenable to table olive harvest. Recent trials with a modified canopy harvester engineered by AgRight (Madera, CA)/Korvan (Lynden, WA) and modified by Dave Smith Engineering (DSE, Exeter, CA) (Fig. 1) removed fruit with 90% efficiency where fruit was accessible (Ferguson et al., 2006), although fruit damage was still at unacceptable levels. To reduce olive damage, the canopy harvester was modified by the incorporation of padding material to rods and other surfaces likely to contact fruit.
The Korvan/DSE harvester is designed to remove fruit by vibrating the canopy with rods attached radially to the axis of three drums (Fig. 2). Drums are oriented parallel to the tree axis or at ≈45° to the tree axis at the top of the tree. Rods penetrate the canopy on one side of the tree and shake with a predominantly oscillatory movement in the plane of the rods. While this movement is intended to remove fruit with little direct interaction between the rods and fruit, it is inevitable that rods, branches, and olives contact each other, causing mechanical damage to the fruit. Padding material encasing the rods is expected to reduce that damage; however, no documented analysis of the padding quality, or how it might be modified, exists.
Harvester–canopy interaction is a fast and complex process in which a large number of elements are implicated. Thus, high-speed image analysis allows us to study this interaction between short periods of time. Each element position can be calculated by a stereo vision method using two images from different viewpoints based on the triangular measurement principle. This method has been applied in agriculture for estimation of plant geometric attributes (Andersen et al., 2005), location of fruit on trees (Jiménez et al., 2000; Takahashi et al., 2002), and implementation of harvesting robots (Tanigakia et al., 2008; Van Henten et al., 2003).
The main objective of this study was the identification and evaluation of olive damage sources produced in the canopy–harvester interaction to evaluate and recommend alterations to the harvester, while identifying the nature and magnitude of olive fruit damage as a result.
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