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Gladis M. Zinati, John Dighton and Arend-Jan Both

We tested the effects of using an inoculum containing natural ericoid roots and soil (NERS) with two fertilizer and irrigation rates on plant growth, shoot (stems and leaves) nutrient concentration, leachate quality, and mycorrhizal colonization of container-grown Coast Leucothoe [Leucothoe axillaris (Lam.) D. Don] and Japanese Pieris [Pieris japonica (Thunb.) D. Don ex G. Don]. Uniform rooted liners were grown in 10.8-L containers in a pine bark, peatmoss, and sand (8:1:1 by volume) substrate medium in a randomized complete block design with four replications. A controlled-release fertilizer, Polyon® Plus 14-16-8 (14N–7P–6.6K), was incorporated in the substrate medium at the 100% manufacturer's recommended fertilizer rate [representing high fertilizer rate (HF)] (56 g per container) to supply 7.84 g nitrogen (N) and at 50% the manufacturer's recommended rate [representing low fertilizer rate (LF)]. Plants were irrigated using a cyclic drip irrigation system at high (HI) and low (LI) irrigation rates calibrated to supply 25.2 L of water and 16.8 L per week, respectively. On average, NERS inoculation increased shoot growth of Leucothoe and Pieris by 56% and 60%, respectively. Shoots of Leucothoe inoculated with NERS had higher N, phosphorus (P), magnesium (Mg), and manganese (Mn) concentrations than non-inoculated plants. At LF, nitrous-N (NOx-N) and orthophosphorus (PO4-P) concentrations in the leachate were reduced by 53% from Leucothoe and 62% from Pieris compared with HF-treated plants. A reduction of 37% and 36% in PO4-P concentration in leachates from Leucothoe and Pieris, respectively, were achieved at the reduced irrigation (LI) rate. The NERS inoculation reduced PO4-P concentrations in leachate from Leucothoe by 26% and NOx-N concentration by 33% in leachates from Pieris compared with non-inoculated plants. Compared with plants grown in the HI–HF treatment, the combination of LI–LF treatment reduced NOx-N concentrations in leachates from Leucothoe by 60% (P = 0.016) and reduced PO4-P leachate concentrations from Pieris by 72% (P = 0.0096). Decreasing the fertilizer rate to 50% of the recommended rate and the irrigation rate to 67% of the recommended rate in conjunction with the incorporation of NERS reduced leachate nutrient concentrations of two main water pollutants (NOx-N and PO4-P). Adopting the practice of adding NERS containing fungi and bacteria can be an effective system to increase shoot dry weight, allow reduction in fertilizer application, conserve water for irrigation, and minimize subsequent nutrient runoff in nursery operations.

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Matthew G. Blanchard, Erik S. Runkle, Arend-Jan Both and Hiroshi Shimizu

Many greenhouse growers have installed retractable energy curtains to reduce energy losses and heating costs. We performed experiments to quantify the effect of retractable nighttime curtains on plant shoot-tip temperature of New Guinea impatiens (Impatiens hawkeri Bull.) grown in glass-glazed greenhouses during winter. Plants were grown in separate greenhouses under different curtain materials and the following measurements were collected: plant shoot tip, aerial wet and dry bulb, and cover (glazing and superstructure or curtain) temperature; net canopy radiation (250 to 60,000 nm); transmitted shortwave radiation (SWR; 300 to 3,000 nm); and air velocity. At night, plants under an extended curtain had a higher (by 0.5 to 2.3 °C) shoot-tip temperature and the net longwave radiation (LWRnet; 3,000 to 100,000 nm) was 70% to 125% greater than plants without a curtain. Shoot-tip temperature was 0.2 to 0.6 °C lower under a shading curtain with open-weave construction (high air permeability) compared with closed-weave constructed curtains (e.g., blackout). As cover temperature decreased from 21 to 12 °C, measured shoot-tip temperature and LWRnet decreased by a mean of 3.0 °C and 39.1 W·m−2, respectively. Under a vapor pressure deficit (VPD) of 0.4 to 0.9 kPa, plant shoot-tip temperature was a mean of 1.0 °C closer to dry-bulb temperature compared with plants under a VPD of 1.4 to 1.8 kPa as a result of decreased transpiration. During the day, shoot-tip temperature was 1.2 °C lower than dry-bulb temperature when transmitted SWR was less than 100 W·m−2 and on average 1.6 °C higher than the dry-bulb temperature when SWR was more than 100 W·m−2. Therefore, in addition to reducing greenhouse heating costs, a curtain extended at night over a crop of New Guinea impatiens could increase plant shoot-tip temperature and accelerate development.

Free access

Helen C. Thompson, Robert W. Langhans, Arend-Jan Both and Louis D. Albright

`Ostinata' Butterhead lettuce (Lactuca sativa L.) was used to study lettuce production at varied shoot (air) and root (pond) temperatures. A floating hydroponic system was used to study the influence of pond temperature on lettuce growth for 35 days. Pond water temperature setpoints of 17, 24, and 31 °C were used at air temperatures of 17/12, 24/19, and 31/26 °C (day/night). Pond temperature affected plant dry mass, and air temperature significantly affected growth over time. Maximum dry mass was produced at the 24/24 °C (air/pond temperature) treatment. Final dry mass at the 31/24 °C treatment did not differ significantly from the 24/24 °C treatment. The 24 °C pond treatment maintained market quality lettuce head production in 31 °C air. Using optimal pond temperature, lettuce production was deemed acceptable at a variety of air temperatures outside the normal range, and particularly at high air temperatures.

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Arend-Jan Both, Bruce Bugbee, Chieri Kubota, Roberto G. Lopez, Cary Mitchell, Erik S. Runkle and Claude Wallace

Electric lamps are widely used to supplement sunlight (supplemental lighting) and daylength extension (photoperiodic lighting) for the production of horticultural crops in greenhouses and controlled environments. Recent advances in light-emitting diode (LED) technology now provide the horticultural industry with multiple lighting options. However, growers are unable to compare technologies and LED options because of insufficient data on lamp performance metrics. Here, we propose a standardized product label that facilitates the comparison of lamps across manufacturers. This label includes the photosynthetically active radiation (PAR) efficacy, PAR conversion efficiency, photon flux density output in key wave bands, as well as the phytochrome photostationary state (PSS), red/far red ratio, and graphs of the normalized photon flux density across the 300–900 nm wave band and a horizontal distribution of the light output.

Open access

Yuan Li, Arend-Jan Both, Christian A. Wyenandt, Edward F. Durner and Joseph R. Heckman

Although not considered an essential nutrient, silicon (Si) can be beneficial to plants. Si accumulator species such as pumpkin (Cucurbita pepo var. pepo) can absorb Si from soil. Si uptake may reduce plant susceptibility to fungal diseases such as cucurbit powdery mildew (Podosphaera xanthii and Erysiphe cichoracearum). We previously reported that wollastonite, an Organic Materials Reviews Institute–approved natural mineral, can increase soil Si level, increase soil pH, provide pumpkin plants with Si, and increase their resistance to powdery mildew. In this study, we examined the optimum application rate of wollastonite for pumpkins grown in pots and exposed to cucurbit powdery mildew. We confirmed that wollastonite has liming capabilities similar to regular limestone. Regardless of the application rates, wollastonite and limestone showed similar effects on soil chemistry and plant mineral composition. Pumpkin plants grown with the lower doses of wollastonite amendments (3.13 and 6.25 tons/acre) had the greatest tissue Si concentrations and demonstrated the greatest disease resistance. We conclude that wollastonite is a useful material for organic cucurbit (Cucurbitaceae) growers who want to increase soil pH and improve plant resistance to powdery mildew at the same time. Applying wollastonite at rates beyond the amount required to achieve a desirable soil pH for pumpkin production did not further increase Si uptake, nor did it further suppress powdery mildew development.