Commercial production of globe artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori] in the United States is almost exclusively in California with major areas located along the central and south coast, the Coachella Valley in the southern inland desert, and the central valley. The total cultivated area has shown a decline in the last 2 years, from 3480 ha in 2009 to 2990 ha in 2011 (U.S. Department of Agriculture, 2012). However, the average yield has increased to 14,570 kg·ha−1 with a total crop value of $48.5 million in 2011. A small number of hectares is also grown in the semiarid areas of the Wintergarden and Lower Rio Grande Valley regions of Texas and Yuma county in Arizona.
In semiarid regions, artichoke is typically grown as annuals (seed propagation transplants) for 6 to 7 months. Transplants are set in the field in single lines on raised beds at 0.45 to 0.75 m in-row and 1.6 to 2.0 m between-row spacing (Schrader et al., 1992; Schrader and Mayberry, 1992; Socrat and Jani, 2000). Artichoke plants develop a dense and large foliage biomass with a canopy reaching up to 2 m wide and 1 m high at maturity for the early cultivar Imperial Star or even higher for new hybrid cultivars (Ryder et al., 1983). Optimizing plant density and planting configuration (arrangement between and within rows) are important cultural practices of vegetable production because of their effects on plant growth, yield, and quality (Caliskan et al., 2009; Jett et al., 1995; Leskovar et al., 2012; Nerson, 2002). Low plant stands can significantly reduce yield and economic returns as a result of inefficient use of resources, whereas high density may lead to plant competition for growth resources (Schotzko et al., 1984). Studies have been published on plant density for several vegetable crops including bell pepper (Capsicum annuum L.) (Cavero et al., 2001; Locasio and Stall, 1994), onion (Allium cepa L.) (Leskovar et al., 2012; Russo, 2008), muskmelon (Cucumis melo L.) (Nerson, 2002), and broccoli (Brassica oleracea L.) (Francescangeli et al., 2006). In artichoke, Miguel et al. (2004) evaluated early- and late-maturing cultivars at 0.6 × 1.67 m and 1.2 × 1.67 m (in-row × between-row). Increasing planting density increased early but not total yield for early cultivars, whereas it did not affect either early or total yield for late cultivars.
Santoiemma et al. (2004) reported that yield of artichoke was unaffected by within-row plant spacing of 0.5 to 1.4 m, although the total number of heads per unit area increased with closer spacing. Also Mauro et al. (2011) found that total head number based on area planted increased and early harvest yield decreased with increasing plant density over a range of 1.0 to 1.8 plant/m2. In terms of planting configuration, Sayre (1959) found that tomato (Lycopersicon esculentum Mill.) plants in twin rows produced a high-quality crop with few fruit defects as compared with standard single rows. In bell pepper, Kahn and Leskovar (2006) reported that a fixed plant population in a single-row arrangement resulted in an increase of full-season production as compared with double-row arrangement. In artichoke, planting configuration has received very little attention, except for a study in Italy where a single-row arrangement increased artichoke earliness and total head number per unit area as compared with a double-row arrangement (Mauro et al., 2011).
Plastic mulches are attractive in the cultivation of numerous horticultural crops. The benefits of using plastic mulch include improved weed control, reduced evaporation and fertilizer leaching, savings in irrigation water, and prevention of diseases and insect vectors. These combined benefits result in enhanced plant growth, cleaner fruits, and earlier and higher yields (Díaz-Pérez and Batal, 2002; Ham et al., 1993; Kasirajan and Ngouajio, 2012; Lament, 1993). Other studies (Díaz-Pérez and Batal, 2002; Hatt et al., 1995; Lament, 1993) also reported that black mulch greatly enhanced root-zone temperature during spring, which might be beneficial to globe artichoke, because it is typically grown during the winter/spring season of the year (Basnizky, 1985; Shinohara et al., 2011).
Research on the combined effects of black plastic mulch and planting configuration on globe artichoke in southern regions of the United States has not been reported. The aim of this 3-year study was to determine plant growth, physiology, head yield, and yield components in response to planting configuration and plasticulture of two artichoke cultivars differing in maturity.
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