Florida is a principal producer of strawberry (F. ×ananassa Duchesne) in the United States. The state ranks second behind California in terms of total production, and during the 2015–16 growing season, a total of 108 million kg of strawberries were harvested from 4411 ha, producing a farm gate value of $291 million (USDA-NASS, 2017). In recent years, the Florida strawberry industry has faced pressure from a 4-fold increase over 10 years (2004–14) in berry shipments from Mexico, volatile markets, and increased production costs (Suh et al., 2017). The combination of increased production costs, lower prices, and volatile markets threatens the industry. The situation suggests that an alternative production system that increases grower income, reduces income risk, and reduces production cost is needed for Florida growers.
In Florida, strawberry is cultivated as a winter annual crop on raised beds that are fumigated and covered with plastic mulch and fitted with drip irrigation. The plasticulture system has numerous benefits, including increased soil temperature, reduced soil evaporation, improved fertilizer-use efficiency, soil conservation, and weed suppression. All these factors combined promote crop growth and increase yield (Anikwe et al., 2007; Ashrafuzzaman et al., 2011; Hou et al., 2010; Lament, 1993). The plastic mulch is typically removed at the end of the growing season and a cover crop is planted on most farms during the fallow period (Boyd and Reed, 2016; Nyoike and Liburd, 2013). Strawberry is one of the most expensive crops to produce due in part to the high costs of land preparation, fumigation, plastic mulch, transplants, fertigation, and pest management (Waterer et al., 2008; Whitaker et al., 2011).
One way to reduce production costs is to grow more than one crop on the same plastic mulch before its disposal. This approach distributes the input costs over multiple crops (Nyoike and Liburd, 2013; Santos et al., 2008) and may increase farm revenue and reduce farm income risk due to the diversification effect. This can be achieved by planting the second crop in the same field before (relay cropping) or after (multicropping) strawberry crop termination (Ngouajio and Ernest, 2005; Santos et al., 2008). Relay-cropping on the same plastic mulch might be particularly beneficial to Florida growers because relatively warm weather and a long growing season makes it possible to grow two or more crops on the mulch within a single calendar year. In Florida, almost all of the strawberry production occurs in Hillsborough County. In this region, strawberries are typically planted between September and early October, and harvested from December through March or early April. Muskmelon (C. melo L.) is a short-season crop and can be planted in late spring or early summer in Florida. Growers frequently transplant muskmelon into strawberry beds that they are still harvesting. In early to mid-March the strawberries are removed by hand and the muskmelons are left to grow. The inclusion of relay-crops such as muskmelon in strawberry-based cropping system may have a positive or negative effect on summer annual weed management. On the one hand, relay-cropping limits the herbicides that can be used and provides a longer season for weeds to emerge in the transplant holes and in the row middles. On the other hand, leaving the plastic mulch in place for a longer period inhibits weed germination and could disrupt the life cycle of some species. To our knowledge, there are no studies that have examined the viability of the different fallow period treatments used by growers in the presence or absence of a relay-crop. The authors are also unaware of any published research that examines the effect of these unique cropping systems on weed density within the crop.
A wide variety of rotations and cover crops have been used to reduce weed (Adler and Chase, 2007; Cho et al., 2015; McSorley et al., 2008; Price and Norsworthy, 2013) and plant-parasitic nematode populations (Wang et al., 2002, 2006, 2007), and many of these, particularly legumes, increases soil fertility for the subsequent crops (Wang et al., 2006). Sunn hemp (C. juncea L.) is a legume cover crop and is thought to have important effects on weed population dynamics (Cho et al., 2015; McSorley et al., 2008; Price and Norsworthy, 2013). Sunn hemp establishes quickly and accumulates shoot biomass rapidly and is an excellent cover crop for weed suppression (Cho et al., 2015; McSorley et al., 2008; Mosjidis and Wehtje, 2011). Sunn hemp is low maintenance and requires no attention after planting until harvest (White and Haun, 1965). Moreover, integration of sunn hemp as a cover crop may reduce weed emergence and growth through release of allelochemicals (Adler and Chase, 2007; Javaid et al., 2015; Skinner et al., 2012). Therefore, the use of sunn hemp in a fallow period may shift the composition of weed seed bank and increase the crop productivity in a rotation program. To our knowledge, no studies have investigated the weed management effects associated with practical integration of sunn hemp into a strawberry rotation system.
The objectives of this research were 1) to evaluate the effect of relay cropping muskmelon with strawberry on strawberry yield or weed population dynamics, 2) to compare the effectiveness of sunn hemp cover crop and chemical fallow programs on the weed densities in the subsequent strawberry or muskmelon crop, and 3) to evaluate the effect of relay cropping 2–4 crops using the same plastic mulch on crop yields.
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