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  • Author or Editor: Charlie L. Rohwer x
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Carrots (Daucus carota L. var sativus) in the midwestern United States are generally raised commercially on sandy-loam or muck soils. Some smaller growers may not have the luxury of an ideal soil type, so raised beds are often recommended to improve taproot growth. To determine specific yield and shape responses of carrots to raised-bed culture in heavy soil, three hybrids (‘Cupar’, ‘Envy’, and ‘Naval’) were grown in 2019 and 2020 on raised or flat beds in clay-loam soil. In addition, two seeding rates (high or low) were incorporated into the split-split plot design. ‘Cupar’ was larger and less misshapen than the other hybrids, but total marketable yields were similar among all three. ‘Naval’ was the most cylindrical. High seeding rate generally resulted in more numerous but smaller marketable roots and no change in total marketable weight. Raised beds caused a 10.6% increase in total marketable weight by allowing more marketable roots classified as “short” (between 76 and 127 mm long, diameter >25 mm) to grow to lengths more than 127 mm long. The average taproot cylindricity was increased and diameter decreased by growing on raised beds. Soil penetration resistance at 7.6 cm was correlated with many of the measured responses.

Open Access

Nonpoint-source phosphorus (P) from agricultural fields is a contaminant of surface waters, and high soil P fertility exacerbates this problem. Many vegetable growers and gardeners have a history of applying more P than is necessary for optimum plant growth. Avoiding unnecessary P applications is an important part of the long-term solution to reducing P loading in water. When soil P levels are very high, management practices that result in more intense P removal are recommended to reduce these levels and the potential for aquatic ecosystem contamination with P. Growers may apply soluble starter fertilizer containing P to encourage rapid transplant establishment; however, the effectiveness of this practice is unknown for soil P levels considered high or very high. Grafting tomatoes (Solanum lycopersicum L.) onto vigorous rootstocks may help the plant remove more P from the soil than nongrafted plants. This study investigated the effects of organic starter P fertilizers applied to three hybrids of nongrafted tomato and the same hybrids grafted onto ‘Estamino’ rootstock in field-grown conditions during three site-years with high preplant P fertility. The yield, fruit P concentration, and amount of P removed from the field were measured to elucidate starter P and grafting impacts on P removal. Starter P was not impactful on all responses. Grafting increased the total yield by 11.6%, fruit P concentration in a genotype-dependent manner (average of 12.6%), and net P removal from the field by 28.4% (6.0 kg P/ha). Net P removal was positively correlated with the total yield (r = 0.821) and fruit P concentration (r = 0.502), suggesting that practices to increase the yield or P concentration independently increase net P removal.

Open Access

Shading has been used to produce high-quality lettuce (Lactuca sativa) in locations where production conditions are not optimal for this cool-season crop. To learn what additional benefits shading provides if heat-tolerant cultivars are used and to understand the effects of shading on growth, sensory quality, chemical content, and transcriptome profile on heat-tolerant lettuce, we grew two romaine lettuce cultivars with and without shading using 50% black shadecloth in 2018 and 2019. Shading reduced plant leaf temperatures, lettuce head fresh weights, glucose and total sugars content, and sweetness, but not bitterness, whereas it increased lettuce chlorophyll b content compared with unshaded controls. Transcriptome analyses identified genes predominantly involved in chlorophyll biosynthesis, photosynthesis, and carbohydrate metabolism as upregulated in unshaded controls compared with shaded treatments. For the tested cultivars, which were bred to withstand high growing temperatures, it may be preferable to grow them under unshaded conditions to avoid increased infrastructure costs and obtain lettuce deemed sweeter than if shaded.

Open Access