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Fahrurrozi Aziz and Katrine A. Stewart

The types of plastic mulch used in horticultural production often fulfill only a few of the grower's needs. Black plastic mulch controls weeds, but can burn young plants. Clear mulch, while warming the soil and enhancing early crop growth, allows prolific weed growth and development. Accordingly, an experiment using a randomized complete-block design with-four replications was set up to compare the effects of black, microperforated black, silver, and wavelength-selective (IRT-76) green mulches, and bare soil on weed growth and development, and on soil temperature and moisture. Each mulch was evaluated for its optical properties. All mulches significantly reduced final stands of seeded weeds compared with bare soil. IRT-76 green had the warmest mean soil temperatures, followed by silver, black, and microperforated black mulches, and bare soil. Soil moisture content was generally higher under plastic mulches than bare soil.

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Sylvie Jenni and Katrine A. Stewart

Quebec vegetable growers are increasingly using agricultural plastics (plasticulture) not only for gains in crop yield, earliness, and quality, but also for weed control and water and fertilizer conservation. Curcubitaceae include heat-loving crops that respond well to plasticulture. Melons are among the most responsive of all crops because they are sensitive to both low soil and air temperatures and to wind, but are very tolerant of high temperatures. The objective of this project was to develop a bioeconomic model that will predict the yield and timing of a melon crop under a number of mulch/tunnel combinations, evaluate the profitability of each production regime, and establish the optimal combinations that will maximize profit and continuity of supply over an extended growing season. A compartment model representing state, rate, and driving variables will be presented.

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Dagobiet Morales and Katrine A. Stewart

The effect of applying saline water (2.5 dS·m-1) via a drip irrigation system at different growth stages of mulched or nonmulched bell peppers (Capsicum annuum L. var. Red Knight) was investigated under greenhouse conditions. The study 6 × 2 factorial was arranged as a randomized complete-block design. The six irrigation treatments were: 1) control—nonsaline water throughout growth; 2) saline irrigation throughout growth; 3) saline irrigation from transplanting until formation of the first fruit set; 4) saline irrigation from transplanting until appearance of the first flower and from first harvest to final harvest; 5) saline irrigation from appearance of the first flower until first harvest; and 6) saline irrigation from fruit set until final harvest. A measurement of stomatal conductance (gs), transpiration (E), and photosynthesis (A) rates was performed during vegetative growth, at flowering, at fruit set, and during fruit growth and development. Mulched plants had higher photosynthetic rates than nonmulched plants, although values were only significant for treatments 2, 3, 5, and 6. In addition, nonmulched plants were slower to recover after periods of saline irrigation than mulched plants. Mulched plants had significantly greater yields than nonmulched plants regardless of irrigation treatment. Saline irrigation when applied throughout growth or from fruit formation until harvest reduced marketable yields by 38% and 45% compared with the control plants.

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Dagobiet Morales-Garcia* and Katrine A. Stewart

In order to examine the effects of saline water (0.2, 1.5, 4.0, 6.5 and 9.0 dS·m-1) without or with plastic mulch (black or green infrared transmitting) on the physiology and yield of bell peppers (Capsicum annuum L. var. Red Night), plants were drip irrigated and grown in greenhouse conditions. Salinity did not significantly decrease the rate of photosynthesis until fruit set after which irrigation with 6.5 and 9.0 dS·m-1 reduced rates by 35%-38% and during fruit development by 50% compared with the control treatment. Plants receiving 4.0 dS·m-1 had significantly lower (30%) photosynthetic rates than the control during fruit development. Stomatal conductance decreased as the rate of salinity increased which in turn affected transpiration. No consistent differences in photosynthesis, stomatal conductance and transpiration rates were obtained with or without plastic mulch. The marketable yield was negatively affected as salinity increased having being reduced by 17%, 64%, 96%, and 100% for saline treatments compared with the control. The number of fruit of fruit per plant was significantly lower at rates of 4.0 dS·m-1 or higher. No significant differences were detected among plastic mulches and non-mulch condition in marketable yield and number of fruits. Water consumption decreased as salinity level increased with decreases of 11%, 20%, 38%, and 52% of the control value. Mulching the soil reduced water consumption by 30% compared with bare soil.

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Fahrurrozi Aziz, Katrine A. Stewart and Sylvie Jenni

Temperature modification is the most investigated environmental factor considered to affect muskmelon (Cucumis melo L. Reticulatus Group) growth in a mulched minitunnel production system. Until now, effects on CO2 concentrations within the tunnel have been ignored. Experiments on production of `Earligold' netted muskmelon were conducted in 1997, 1998, and 1999 to determine daily CO2 concentrations for 10 mulched minitunnel and thermal water tube combinations. Carbon dioxide concentrations under nonperforated (clear or infrared-blocking polyethylene) tunnels were significantly higher (three to four times) than that of ambient air. Soil respiration under the plastic mulch was primarily responsible for increased CO2 levels in the tunnel. Daily CO2 concentrations in the tunnels varied little during early muskmelon growth, but fluctuated widely as the plants developed. Ventilation significantly decreased CO2 concentrations in the tunnels but levels remained significantly above the control and perforated tunnel treatments. When using mulched minitunnels for muskmelon production, daily CO2 concentrations should be recognized as a significant factor influencing growth.

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Fahrurrozi Aziz, Katrine A. Stewart and Sylvie Jenni

Field experiments were conducted during 1997, 1998, and 1999 to determine effects of 10 combinations of mulched minitunnel and thermal water tube on air, soil, and water-tube temperatures and on vegetative growth of `Earligold' netted muskmelon (Cucumis melo L. Reticulatus Group) within the tunnels. Use of mulched minitunnels significantly increased air, soil and water temperatures during the preanthesis phase in all years compared with control treatments. Inclusion of water tubes and venting the tunnels decreased air temperature fluctuations in the tunnels. During the first 10 to 15 days after transplanting, plants grown in nonperforated tunnels had higher relative growth rates (RGRs), net assimilation rates (NARs), and dry weights (DWs) than those grown under perforated tunnels and control plots. Plants in tunnels containing thermal water tubes generally had higher RGRs, NARs, and DWs than those without tubes. During the later part of the experiment, from 11 to 16 days after transplanting until anthesis, however, there were no consistent effects of mulched minitunnels on RGR, NAR, and plant DW. Tunneled muskmelons had significantly higher RGRs, but generally lower NARs than those grown without tunnel. Use of mulched minitunnels significantly increased plant DW at anthesis in 1997, but not in 1998 and 1999. Plants grown in the minitunnels containing a thermal water tube generally had higher RGRs, NARs, and DWs than those without water tubes. Ventilating nonperforated tunnels generally increased RGR, NAR, and plant DW. Plants grown in the tunnels reached anthesis 10 days earlier than those without tunnels.

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Ray A. Watson, Katrine A. Stewart and Valentin Furlan

The effects of two mycorrhizal species (Glomus versiforme and Glomus intraradix) and a control on the growth of green pepper, Capsicum annuum, and lettuce, Lactuca sativa, seedlings have been evaluated using three types of growing media (Fafard bulk mix, Cornell mix and a compost based mix) and two types of containers, Cell Packs (125 cubic cm volume) and Pro-Trays (65 cubic cm volume) for green pepper and Cell Packs (125 cubic cm volume) and Plug Flats (33 cubic cm volume) for lettuce. The experiments used a split plot randomized complete block design with 4 blocks, and were carried out in a double-poly greenhouse in 1991. Supplemental lighting was provided by HPS lights with a 16 hour photoperiod. Seeds were sown directly into the containers of mycorrhizal inoculated media. All treatments received the same fertilizer regime. Plants in the higher volume cells were larger than those in the smaller volume cells for both pepper and lettuce. The Fafard Bulk Mix and the Compost mix gave larger plants than did the Cornell mix for both crops. An additional experiment examining the effect of light type on mycorrhizal transplant growth and development is underway and will be presented.

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Ray A. Watson, Katrine A. Stewart and Valentin Furlan

The effects of two mycorrhizal species (Glomus versiforme and Glomus intraradix) and a control on the growth of green pepper, Capsicum annuum, and lettuce, Lactuca sativa, seedlings have been evaluated using four types of growing media (Peatwool, Fafard bulk mix. Cornell mix and a compost based mix) and two types of containers, Cell Packs (125 cc volume) and Pro-Trays (65 cc volume) for green pepper and Cell Packs (125 cc volume) and Plug Flats (33 cc volume) for lettuce. The experiments were split plot randomized Complete block design with 6 blocks (lettuce) and 4 blocks (pepper). Seeds were sown directly into the containers of mycorrhizal inoculated media. All treatments received the same fertilizer regime.

Cell volume had no significant effects on green pepper fresh weight, dry weight, stem diameter, leaf area or leaf number but the lettuce Cell Pack plants had significantly higher fresh and dry weights, more leaves and higher leaf area. The Fafard Bulk and the Compost mix gave significantly higher fresh and dry weights than did the other two media for both green pepper and lettuce. Mycorrhizal species did not influence plant growth with the exception of leaf area in green peppers and shoot dry weight in lettuce.

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Sylvie Jenni, Katrine A. Stewart, Gaétan Bourgeois and Daniel C. Cloutier

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Sylvie Jenni, Isabelle Gamache, John Christopher Côté and Katrine A. Stewart

Growers of early stalk celery (Apium graveolens var. dulce) often experience financial losses due to bolting (the premature and rapid elongation of the main celery stem) in temperate regions. A method was developed to provide early warning of bolting in field-grown celery, on the basis of two criteria, one visual and one microscopic, for inflorescence development. Bolting could be detected 40 days after transplanting using the visual criterion, and as early as 30 days after transplanting using the microscopic criterion. Early detection of bolting using the visual and microscopic criteria provided celery growers with periods of, respectively, 25 days and up to 35 days to consider harvesting earlier, before the length of the celery stems exceeded commercial standards. This method could be effective in minimizing financial losses due to bolting when coupled with agro-economic studies.