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Four substrates were investigated for their efficacy as roof garden vegetative layers. The substrates comprised a sandy loam soil (S), sandy loam soil amended with urea formaldehyde resin foam (S:F) in a proportion of 60-40 v/v, sandy loam soil amended with peat and perlite (S:P:Per) in a proportion of 50-30-20 v/v and peat amended with urea formaldehyde resin foam (P:F) in a proportion of 60-40 v/v. The substrates were evaluated for their physical and chemical properties and their capacity to sustain growth of Lantana camara L. Physical and chemical evaluation included weight determination at saturation and at field capacity, bulk density determination, water retention, air filled porosity at 40 cm, pH and EC. When compared to the control (S) a weight reduction of 16.8%, 23.9% and 70.3% was obtained at field capacity with S:F, S:P:Per and P:F substrates respectively. Bulk density was reduced by 46%, 43% and 95%, in substrates S:F, S:P:Per and P:F, respectively, compared to the control substrate S. Air-filled porosity at 40 cm was slightly increased for substrate S:F while it was substantially increased for substrate P:F. The pH response between the initiation and the termination of the study was similar for the four substrates. EC decreased in substrates S and S:P:Per but increased in substrates S:F and P:F. Plant growth was monitored as shoot length, shoot number, main shoot diameter and the number of buds and flowers. Substrates S and S:F resulted in similar plant growth, while substrate S:F promoted flowering. Substrate S:P:Per induced slow plant growth during the first 6 months which subsequently increased resulting in a final growth that was satisfactory and comparable to the S and S:F substrates. Substrate P:F did not support sufficient plant growth and its use should be considered only in special cases where reduced weight of the roof garden is imperative.

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Abstract

Lime or activated charcoal effectively reduced fluoride absorption and increased plant dry weight in lettuce (Lactuca sativa L.), perennial ryegrass (Lolium perenne L.), and spinach (Spinacia oleracea L.) grown in a fertilized perlite-peat moss medium. Lime in combination with charcoal surpassed that of charcoal alone in reducing fluoride absorption and increasing yields. While the addition of lime or charcoal raised the pH of the growth medium only the lime greatly reduced water-soluble fluoride.

Open Access

High levels of sphagnum peat in the growing medium promoted growth of asparagus (Asparagus officinalis L. cv. Viking 2K) in a greenhouse study. Application of NH4NO3 > 1 g/pot (84 kg·ha-1 equivalent) was detrimental to root growth. High N rates and high organic matter levels decreased fibrous root development. Shoot dry weight was highly correlated with fleshy root number, root dry weight, and shoot vigor.

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Fifteen-centimeter (1700-ml) containers were prepared for this experiment by sealing the drainage holes with insect screen (Hummert International, Earth City, Mo.) that had openings of 0.026 cm × 0.0805 cm. Containers were filled with substrates composed of either a 80% sphagnum peat or 80% coir. The remainder of the substrates was composed of perlite. Rooted cuttings of Euphorbia pulcherrima `Freedom' were planted into the containers and the containers were sealed with the insect screen and plants were allowed to grow and the substrate to age for 2 weeks. Fungus gnat (Bradysia spp.) larvae were collected using potato disks placed on the surface of infested substrates. After 3 days, larvae were collected from the disks, and 10 larvae were added per container. Uninoculated controls were included. After a period of 6 weeks, the adult population was sampled by placing 2.5 × 5.0-cm yellow sticky cards in each container. The larval population was sampled by placing a 4-cm-diameter potato disk on the substrate surface of each container. Fungus gnat larvae and adults were recovered from both sphagnum peat and coir-based substrates. Neither the number of adults nor the number of larvae recovered were significantly different between sphagnum peat and coir-based substrates.

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A characteristic problem with peat moss is its difficulty in initial wetting and rewetting, especially in a subirrigation system. Wetting agents improve wetting characteristics primarily by reducing the surface tension of water. This results in a rapid, uniform movement of water by capillary rise through the growing medium.

Two methods were used to compare the effectiveness of different wetting agents: gravimetric and electrical. Ten cm pots containing peat moss were placed in a subirrigation system. The gravimetric method used a laboratory scale where pots were periodically weighed to determine the amount of water absorbed. The electrical method utilized thin beam load cells, which have strain gages bound to the surface, to determine the weight of a suspended object. Load cells were coupled with a Campbell Scientific datalogger to collect data every minute without removing the pot from subirrigation. Because the effect of buoyancy altered the true weights, equations were generated to adjust the water uptake values. Corrected weights were used to create absorption curves for comparison of the slopes to determine which wetting agent has the fastest rate of absorption. The load cell reliably and accurately described the wetting characteristics of Peat moss and we found good agreement with the gravimetric method.

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Abstract

The physical and water-release characteristics of a gasifier residue in combination with bark, Canadian sphagnum peat, and sand were determined. Both gasifier residue and peat had characteristics more favorable for plant growth than bark or sand alone. The combination of gasifier residue and peat produced characteristics superior to gasifier residue or peat alone. Gasifier residue and combinations of gasifier residue and peat had almost twice the available water of a standard nursery medium. The addition of sand or bark decreased the performance of gasifier residue in a number of physical parameters. Unsieved gasifier residue had a particle size distribution suitable for container plant production.

Open Access

“Legend' roses were grown in various potting mixtures of processed fiber (PF, a by-product of anaerobically digested dairy waste), peat moss, pumice, or bark to test the applicability of PF as a substitute of peat moss and bark. A commercial mix (peat moss and bark, 1 to 1 by volume) was used as the control. Plant appearance, growth of leaves, shoots, and flowers were the same in straight PF, commercial mix, and PF mixtures of 50% or less pumice. Plants grown in mixtures of peat moss, pumice, and bark were inferior to those in PF. This study demonstrated that PF media was better than peat moss and bark for rose production.

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Abstract

Chrysanthemum plants (Chrysanthemum morifolium Ramat. cv. Bright Golden Anne) were grown for 84 days in plastic pots containing 6 different media treated with inorganic fertilizers or liquid digested sewage sludge at 50, 100, and 200 ml/week. Plants grown in 1 soil: 1 sand: 1 peat, 1 soil: 1 sand, and 1 soil: 1 peat were similar to each other in size, and larger than plants grown in 1 sand:1 peat, all sand, or all peat. Peat-grown plants were smallest. Plant size and flower diameter decreased with increasing rates of sludge application. Plants fertilized with inorganic sources of fertilizer looked the same as those grown with 50 ml/week sludge (6 mm), except the sludge-treated plants were shorter and had a smaller dry weight. Plants treated with 50 ml/week sludge had flowers with a diameter and dry weight equal to those of flowers grown with liquid or pelletized inorganic fertilizer.

Open Access

Tomato plants (Lycopersicon esculentum Mill. cv. Capello) were grown in peat bags, rockwool slabs, and NFT in a greenhouse to examine the effects of nutrient solution electrical conductivity (EC) and potential evapotranspiration (PET)-dependent EC variation on plant water relations. Peat bags were irrigated by a PET-dependent irrigation system. EC was varied from 1 to 4 mS·cm-1 according to PET under –5 and –9 kPa of substrate water potential setpoints (SWPS). The plants in rockwool and NFT were treated with ECs of 2.5, 4, and 5.5 mS·cm-1. Peat bags and rockwool slabs were overwatered once a week to wash out the accumulated salts. Leaf water potential (ψ1) and relative water content (θ) were measured before and after plants were overwatered. Turgor (P) and osmotic π potentials were estimated from the pressure-volume method. Before plants were overwatered, ψ1 was significantly lower in the plants with high EC and low SWPS treatments and also lower in variable EC-treated plants, but P maintained close to the control value. After plants were overwatered, ψ1 recovered close to the control level and P became higher because of the lower π in the treatments of high EC, variable EC, and/or low SWPS. At a given ψ1 the plants with high EC, variable EC, and/or low SWPS maintained higher θ. The analysis of the pressure-volume curve showed that the leaves treated with high EC, variable EC, and/or low SWPS had higher turgid water content, higher symplasmic (osmotically active) water content, lower apoplasmic (osmotically inactive) water content, and lower θ point of zero turgor (incipient plasmolysis). Maintenance of P after overwatering was directly proportional to photosynthetic capacity. We suggest that osmotic adjustment occurs in response to high EC, low SWPS, or both and that overwatering substrates and varying EC can not only avoid salinity stress, but also improve turgor maintenance.

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Abstract

Four levels of K were applied at weekly intervals to 2 plantings of Matthiola incana (L.) R. Br. grown to anthesis in 3 media. At all levels of K the plants grown in the bark medium had the greatest height, spike length, oven dry weight, and shortest time to anthesis. The optimum tested level was 100 ppm K for plants grown in both the soil mix medium and the peat-lite medium. Differences in plant performance were associated more with media than with levels of K.

Open Access