Eating watermelon (Citrullus lanatus) is a traditional part of the Fourth of July holidays in the United States; however, growing watermelon in Missouri, USA for the local Fourth of July market requires an early growing season start (beginning of April) under protected culture because of low temperatures and the risk of freezing. Therefore, ‘Yellow Doll’ watermelon production was investigated under low tunnel (LT) and caterpillar high tunnel [HT (walk-in movable two-row tunnel)], and the economic feasibility was assessed by marginal analysis for both protected cultures. Planting in early April allowed harvest to start 1 to 2 weeks before the target market date. In addition, yield increased under HT in comparison with LT and open field (Op). Marginal analysis under the conditions of this study and prices obtained from local farmers’ markets showed a positive marginal rate of return for HT in comparison with the control Op. The marginal rate of return sensitivity study suggests that differences in marketable yield of 300–400 and 200–250 lb/1200 ft2 are necessary under HT and LT, respectively, for the protected culture to be economically feasible with watermelon prices above $0.75/lb and/or $1.00/lb as obtained in local farmers’ markets. Therefore, it is possible and there is potential to produce watermelon under protected culture for the local Fourth of July market. A gain in market share with potential premium prices for watermelon may increase the sustainability of small and medium-size specialty crop farmers in Missouri. To accomplish this, it is necessary to use early cultivars (70 to 80 days to maturity), plant in early April with transplants grown in greenhouses, and make sure to manage tunnels properly to maintain favorable growing conditions, protect against freezing temperatures and ensuring good pollination.

Low tunnels (LTs) enhance vegetative growth and production in comparison with open field, but it is not known whether nitrogen (N) requirements and use efficiency increase or decrease for optimal crop performance. Therefore, the purpose of this study was to determine differences in N requirement, uptake, and use efficiency in basil grown under LTs compared with open field. The experimental design each year was a split plot with four replications. The main effect (plots) was N fertilizer application rate (0, 37, 74, 111, 148, and 185 kg·ha−1) and the secondary effect (subplots) was production system (LTs covered with spun-bonded rowcover vs. open field). Plant height and stem diameter were greater under LT than open field; however, they were unaffected by N fertilizer rate. Total fresh and dry weight increased with LT by 61% and 58% and by 50% and 48% in 2017 and 2018, respectively. Optimum N rates for fresh weight (98% of peak yield) were 124 and 104 kg·ha−1 N under LT and open field, respectively. Leaf N concentration decreased under LT, but total plant N uptake increased because of increased dry weight. Without fertilization, soil available N use efficiency (SNUE) for dry weight increased by 45% and 66% in 2017 and 2018, respectively. Mixed results were obtained for N fertilizer use efficiency (NFUE) in response to N rate. In conclusion, LT increased summer production of sweet basil, total plant N uptake, and SNUE.

Low tunnels covered with spun-bonded fabric (row covers) provide season extension for vegetable production and also afford a physical barrier against airborne insects and other non-soil pests. Brussels sprouts, Brassica oleracea L. group Gemmifera (Brassicaceae), is a popular vegetable in local markets in Virginia; however, unprotected field production is severely affected by insect pest infestation. This study's objective was to determine the level of protection low tunnels provide against insect infestation and leaf herbivory injury. The experiment was conducted at the Virginia Tech Eastern Shore Agricultural Research and Extension Center in Painter, Virginia. The experimental design was split-plot with polyethylene soil mulches (white or black) as whole plot factors and production systems (low tunnel or open field) as subplot factors. In this study, low tunnels reduced insect infestation and chewing herbivory leaf injury to Brussels sprouts. Compared to an unprotected open field, infestations of lepidopteran insects and harlequin bug, Murgantia histrionica (Hahn) (Hemiptera: Pentatomidae) were reduced on plants under low tunnels. However, aphids (Hemiptera: Aphidae) infestation occurred under low tunnels in fall. There was no effect of color mulches (white or black) and no interaction between tunnel and mulch color on insect infestation and chewing injury. Fewer insect infestations and feeding injury indicate that low tunnels can be an effective management tool for sustainable vegetable production.

Farmers use low tunnels (LTs) covered with spunbonded fabric to protect warm-season vegetable crops against cold temperatures and extend the growing season. Cool season vegetable crops may also benefit from LTs by enhancing vegetative growth and development. This study investigated the effect of the microenvironmental conditions under LTs on brussels sprouts growth and production as well as water requirements and use efficiency in comparison with those in open fields. Low tunnels increased minimum soil temperature in all trials. By contrast, LTs reduced evapotranspiration (ET) 54% to 68% by reducing solar radiation (SR) and blocking wind in spite of increased maximum air temperatures. Because of reduced ET, water needs and irrigation decreased by 24% to 40%. Furthermore, LTs enhanced vegetative growth (plant leaf area, plant height, and plant dry weight). Sprouts per plant and yield under LTs increased by 29% and 46% in Spring 2017, by 22% and 46% in Fall 2017, and by 29% and 22% in Spring 2018. Considering the increased growth and productivity and reduced irrigation, LTs increased water-use efficiency (WUE) in relation to yield by 62% to 107% in comparison with open fields. Increased total yield and improved WUE illustrate that LTs may be a useful management tool in sustainable production systems in addition to their traditional role for season extension.

Soil moisture deficit at early season is detrimental for sweetpotato growth and development affecting final yield. This study investigated the effects of different soil moisture regimes on early season growth, developmental, and physiological responses of two sweetpotato cultivars, 'Beauregard' and 'Evangeline', grown in a greenhouse environment. Five levels of soil moisture treatments, 0.256, 0.216, 0.164, 0.107, and 0.058m(3) m(-3) of VWC, were maintained through sensor-based soil moisture monitoring, and semiautomated programmed irrigation. Midday leaf water potential (LWP), gas exchange, and fluorescence were measured weekly from 30 to 50 days after transplanting (DAT). Growth and development of plants were evaluated through harvesting four plants at 5-day intervals from 14 to 50 DAT. Leaf pigments and cell and chlorophyll stability indices were also determined. Midday LWP of sweetpotato declined linearly with decreasing soil moisture levels. The photosynthetic rate also declined linearly in Beauregard and quadratically in Evangeline with decreasing soil moisture. Both cultivars had a close association between photosynthetic rate and stomatal conductance over the soil moisture treatments, suggesting that stomata] closure is a key limitation for the drop in photosynthesis. Chlorophyll concentration was significantly lower at extreme soil moisture deficit conditions. Significant difference was found in water use efficiency between cultivars and among soil moisture treatments. Rates of vine elongation and leaf formation of Evangeline decreased more rapidly than Beauregard with declining soil moisture levels. Also with decreasing soil moisture, the shoot biomass declined more rapidly than root biomass. The results showed that maintaining soil moisture closer to field capacity (0.256 m(3) m(-3) of VWC) during early season is beneficial for early development of both root and shoot system and thus better crop performance. The data and the inferences derived from the functional algorithms developed in this study will be useful for crop modelling, field-level irrigation scheduling, and planting decisions. (C) 2014 Elsevier B.V. All rights reserved.

Temperature impacts several growth and developmental processes in sweetpotato [Ipomoea batatas L. (Lam)] including storage root (SR) initiation. To quantify early season growth and developmental responses of sweetpotato, an experiment was conducted using sunlit growth chambers at a wide range of day/night temperatures, 20/12, 25/17, 30/22, 35/27, and 40/32°C, from transplanting to 59 d using cultivar Beauregard. Growth and developmental rates were estimated from plants harvested at regular intervals. Total and SR numbers recorded at each harvest were analyzed by fitting sigmoidal curves to estimate SR initiation rates. With increasing temperature, SR conversion efficiency increased quadratically with an optimum at 23.9°C. Adventitous and SR developmental rates were increased linearly and quadratically, respectively, with increasing temperature, and maximum rate of SR initiation was reached at 29.5°C in 16.7 d. Vine and leaf area growth rates showed quadratic trends with temperature with maximum rates at 29 and 33°C, respectively. While quadratic functions best described temperature responses of total, stem, and SR biomass, the optimum temperatures varied among them at 29.2, 30.1, and 26.5°C, respectively. Leaf biomass, conversely, increased linearly with temperature. Fraction of biomass partitioned to roots declined linearly and at high temperature it declined by 75%, compared to the fraction at SR optimum temperature. The SR production efficiency declined from 0.43 to 0.08 g SR kg−1 total weight, and dropped by 81% at high temperature relative to optimum. Quantified growth and developmental responses derived from the developed temperature‐dependent functional algorithms will be useful to develop sweetpotato crop models and management decisions.