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Georges T. Dodds, Leif Trenholm, Ali Rajabipour, Chandra A. Madramootoo, and Eric R. Norris

In a 2-year study (1993-94), tomato (Lycopersicon esculentum Mill. `New Yorker') plants grown in a sandy loam soil in field lysimeters were subjected to four water table depth (WTD) treatments (0.3, 0.6, 0.8, and 1.0 m from the soil surface). In 1994, precipitation during the flowering stage was far above average and apparently led to waterlogging in the shallowest WTD treatment, while in the drier year (1993), the deepest WTD treatment suffered from drought stress. In general, over the 2 years, the 0.6-m WTD showed the best yields and largest fruit, while the 1.0-m WTD showed the lowest yields and smallest fruit. However, the incidence of catfacing, cracking, and sunscald was generally higher in the 0.6 m WTD treatment and lower in the 1.0-m WTD treatment. Furthermore, fruit firmness was generally greatest for the two deeper WTD than for the shallower WTD. To strike a balance between yield and quality, a WTD of between 0.6- and 0.8-m is recommended for tomato production on sandy loam soils.

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Noreen S. Khoury and E. Jay Holcomb

Greenhouse substrates are designed to allow maximum aeration. Substrate water holding capacity can be increased by media compaction.

Six inch standard pots, fitted with gas tight openings for removing gas samples, were filled with Metromix 350 and Peatwool at 2 different compaction rates. Half the pots were planted with rooted cuttings of Poinsettia pulcherrima `Glory' and half were left fallow. Air samples were taken at both wet and dry soil moisture conditions at early, mid point and at the end of the cropping cycle. In general, wet substrates had higher CO2 than drier substrates and more compacted substrates had higher CO2 than less compacted.

CO2 decreased with time in all treatments. The highest CO2 levels occurred in wet heavily compacted Peatwool with a plant and the lowest occurred in dry Metromix with no plant.

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Mario Perches and Don Wilkerson

Ebb and Flood systems provide an efficient means of sub-irrigating greenhouse crops. However, substrate accumulations of soluble salts can limit plant growth.

Two treatment irrigation regimes, consisting of 1.70 EC and 0.86 EC, were applied to 7.0 cm pots filled with a standard peat:perlite growing medium. Treatment solutions were changed weekly. All containers were irrigated daily and substrate EC levels measured weekly in the upper, middle, and lower 2.33 cms of the container.

Following 6 weeks of observation, mean EC substrate levels ranged from 1.23 mmhos/cm to 4.42 mmhos/cm. Significant differences occurred between the upper and middle/bottom portions of the container. There was also a significant interaction between treatment irrigation regimes, substrate layer and week.

In both treatment regimes, salt accumulations in the middle and bottom layers of substrate were within acceptable levels for plant production.

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Ken Tilt, William D. Goff, David Williams, Ronald L. Shumack, and John W. Olive

Pecan [Carya illinoinensis (Wangenh.) C. Koch `Melrose'] and pear (Pyrus calleryana Decne. `Bradford') trees in the nursery grew more in containers designed to hold water in the lower portion. The water-holding reservoir was obtained either by placing 76-liter containers in a frame holding water to a depth of 6 cm or by using containers with drainage holes 6 cm from the bottom. Continuous waterlogging at the bottom of containers resulted in root pruning and root death in the lower portion of the containers, but roots grew well above the constantly wet zone. Fresh weight of plant tops and trunk diameters were greater after two growing seasons in the containers with water reservoirs compared to those grown in similar containers with no water reservoirs. Total root dry weight was unaffected.

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Mary Ann Rose, John W. White, and Mark A. Rose

`Celebrate 2' poinsettias (Euphorbia pulcherrima Willd.) received either a constant application rate of 200 mg N/liter or a variable rate that was linked to the N accumulation pattern of the crop. At final harvest, shoot N content, N concentration, dry weight, leaf area, and quality were similar for the treatments. However, N recovery efficiency of the variable treatment was greater (58% vs. 38%), and 41% less total N was applied compared to the constant-rate treatment. Growth analysis revealed that N accumulation rates for both treatments increased rapidly as side branches developed, reaching a maximum 50 to 60 days after potting, and decreased throughout bract development. The decrease in N accumulation rates after day 60 reflected a shift in N allocation from leaves to bracts, a tissue with a lower N concentration.

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Daniel I. Leskovar

Irrigation methods, rates, timing, and frequency may influence the physical and chemical properties of the growing media thereby affecting root initiation, elongation, branching, development and dry matter partitioning between roots and shoots.

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Marc W. van Iersel and Krishna S. Nemali

We examined the effectiveness of an elevated capillary mat system to maintain constant and different moisture levels in the growing medium and verify the potential of drought stress conditioning in producing small and compact bedding plants. To differentiate between plant height and compactness, we determined compactness as the leaf area or dry mass per unit stem length. Marigold `Queen Sophia' (Tagetes erecta L.) seedlings were grown in square, 9-cm-wide, 10-cm-high containers filled with a soilless growing medium. A capillary mat was laid on top of a greenhouse bench which was raised by 15 cm on one side compared to the other side to create an elevation effect. Seedlings were subirrigated by immersing the low end of the capillary mat in a reservoir of water. The amount of water moving to the higher end of the mat progressively decreased with elevation. The moisture content in the growing medium averaged from 26 to 294 mL/pot at different elevations. Regression analysis indicated that growth parameters including, shoot dry mass, leaf area, leaf number, and plant height decreased linearly with decreasing soil moisture content in the growing medium. Of all the measured growth parameters, plant height was found to be least sensitive to decreasing moisture content in the growing medium. Plants in high moisture treatments had more dry mass and leaf area per unit length of the stem compared to those in low moisture treatments. Our results indicate that drought stress can produce small, but not truly compact bedding plants.

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Jeremy R. Pinto, Rhiannon A. Chandler, and R. Kasten Dumroese

persist under commercial greenhouses ( McAvoy et al., 1992 ; Molitor, 1990 ) threatening groundwater quality. Consequently, discharges may be legally regulated in the future; such restrictions already exist in Oregon ( Grey, 1991 ). Subirrigation

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Anthony S. Davis, Matthew M. Aghai, Jeremiah R. Pinto, and Kent G. Apostol

through these systems is retained in the containers ( Beeson and Knox, 1991 ). Thus, 60% to 80% of overhead irrigated water is of almost no value for plant growth. In light of this, there is an increasing interest in subirrigation as a viable alternative