Carrots are an economically important crop in the upper midwestern United States, with 3493 ha harvested in Minnesota, Michigan, and Wisconsin in 2017; 84% of the acreage was for processing [U.S. Department of Agriculture (USDA) National Agricultural Statistics Service (NASS), 2020]. Soil compaction generally negatively impacts taproot length and yield (Johansen et al., 2015; Pietola, 1995). Typically, carrots are grown on peat/muck or sandy-loam soils that are deeply cultivated to reduce compaction for encouraging straight, uniform taproots. University extension publications and popular press often advise growers and gardeners to plant carrots on raised beds for similar reasons (Delahaut and Newenhouse, 2011; Jauron and Wallace, 2017; Kelley and Phatak, 2009; Smetanka, 2017; Thompson, 2017). Especially on fine-textured mineral soils (not sandy or peat/muck), it is reasonable to assume that raised beds reduce compaction and soil density where the taproot grows. In addition, raised beds can improve water relations in the root zone, especially in wet soils (Bakker et al., 2005). Water relations early in a carrot crop cycle may influence length potential and straightness of the harvested taproot, especially in heavy soils (Brown and Gracie, 2000). A carrot taproot’s ability to avoid areas of low water availability suggests that after germination, drier surface soil in raised beds may encourage longer taproots. However, data to illustrate the specific effects of raised beds on carrots are lacking.
Weed control in carrots can be especially challenging, because carrot seeds are slow to germinate and a canopy is slow to develop. One strategy to reduce weed pressure is to seed at a higher rate, reducing the time to develop a canopy for shading weed seedlings (Colquhoun et al., 2020). However, increased population causes shorter taproots (Thompson, 1969).
Carrot varieties can be classified by their general shape and use characteristics. For example, Chantenay carrots are generally wide and conical-shaped, with medium-length, and are often recommended over other types for heavy or compacted soils. Imperator carrots are long, and generally perform best on sandy-loam or peat/muck soils, although breeders can recommend specific varieties that may perform well on mineral soils. Nantes-type are highly cylindrical and medium-length. Each type has utility in fresh-market or processing industries.
In this study, three carrot hybrids were grown (Chantenay-type, Imperator-type, and Nantes-type) to determine the effects of raised beds and elevated seeding rates, and the interaction between them, on carrot taproot size, shape, and yield in a clay-loam soil.
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