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William C. Fonteno

The determination of air and water holding capacities of horticultural substrates has been plagued by errors in measurement. The amount of air and water held at container capacity is influenced by the substrate and container height. Container capacity can be established through specific measurement. Air space, the difference between total porosity and container capacity, is usually poorly determined because of errors in total porosity measurement. Most researchers calculate total porosity (St) from the formula: St = 1-(ρbp), where ρb is the dry bulk density and ρp is the particle density. While bulk density is usually measured, particle density is not. Many times an average ρp of 2.65 Mg·m-3 for mineral soils is used. This sometimes creates large errors in calculating total porosity because the values of ρp for horticultural substrates range from 0.35 to 2.1 Mg·m-3. Total porosity can be measured with great accuracy at 0 kPa tension on a pressure plate apparatus, but is costly in equipment and time. Using a modified method of extraction and a new apparatus, using standard aluminum soil sampling cylinders, total porosity was measured with an 85% reduction in time end no decrease in accuracy.

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William C. Fonteno and Paul V. Nelson

Loose rockwool had a total porosity similar to peatmoss (92%, by volume) but with water retention capabilities similar to sand. Root media formulations containing loose rockwool were tested with seven plant species for plant response and nutrient uptake. The volume percent formulation, 20 rockwool : 10 peatmoss : 20 vermiculite : 45 pine bark : 5 perlite, was superior to formulations containing 10% or 30% rockwool. Plant response in this rockwool medium in bedding plant flats was superior to that in two high-performing commercial media for impatiens (Impatiens sultanii Hook), marigold (Tagetes patula L.), and petunia (Petunia hybrida Vilm) and equal to one commercial medium for tomato (Lycopersicon esculentum Mill.). However, response of chrysanthemum (Chrysanthemum × morifolium Ramat.), geranium (Pelargonium × hortorum Bailey), and poinsettia (Euphorbia pulcherrima Willd. ex Kl.) in 1.58-liter pots was inferior to both commercial media in one-half of the trials. Differential plant responses in the root media treatments did not relate directly to differences found to occur in plant nutrient composition. The high initial pH level of rockwool necessitated reduced application of limestone and increased application of calcium sulfate to offset Ca deficiency.

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William R. Argo, John A. Biernbaum, and William C. Fonteno

Medium CO2 and O2 partial pressures were measured at three locations [3.8 (top layer), 7.5 (middle layer), and 10.3 (bottom layer) cm below the rim] in 15-cm-tall pots containing flowering chrysanthemums [Dendranthem×grandiflorum (Ramat.) Kitamura] grown in one of three root media. Average ambient medium CO2 and O2 partial pressures were 63 Pa and 21 kPa, respectively, and were similar in the three sampled layers in root media with an average moisture content of 50% to 60% of container capacity. Within 10 minutes after a drip-irrigation application of well water containing a titratable alkalinity to pH 4.5 of 320 mg CaCO3/liter, the partial pressure of medium CO2 increased to ≤1600 Pa and medium O2 decreased to 20.5 kPa in the top and middle layers of the pot. With subirrigation, medium CO2 partial pressures increased to ≤170 Pa and medium O2 remained at 21 kPa. When reverse-osmosis purified water (titratable alkalinity to pH 4.5 of <20 mg CaCO3/liter) was used instead of well water, the large increase in medium CO2 did not occur, indicating that the bicarbonate alkalinity in the irrigation water was the source of CO2. The high medium CO2 partial pressure measured after irrigation was not persistent; within 180 minutes, it returned to levels averaging 45% higher (100 Pa) than that measured before the irrigation. Medium O2 also had returned to ambient levels 180 minutes after the irrigation.

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Lesley A. Judd, Brian E. Jackson, and William C. Fonteno

Container production of plants use substrates that are formulated to have adequate physical properties to sustain optimal plant growth; however, these properties can change over time as a result of substrate settling and root growth of the growing plant in the container. An apparatus (rhizometer) was developed that measures the changes caused by plant roots on physical properties of substrates during crop production in containers. The design of the rhizometer included a clear core, which allowed for observing and measuring a range of root system characteristics in situ, including total root length visible along the rhizometer. Physical properties of planted and fallow rhizometers were measured, and the effect of four species on substrate physical properties was determined. There was a general decrease in substrate total porosity and air space (AS) over time with both fallow and planted rhizometers as a result of both settling of the substrate and root growth into the substrate. Container capacity did not change over time with or without roots. Plants with large root systems such as Begonia ×hybrida acut. decreased AS over time, whereas plants of Rudbeckia hirta L. with a smaller root system did not have the same effect. Measured total root length was highly correlated to the total dry root mass of Tagetes erecta L. and Zinnia marylandica D.M. Spooner, Stimart & T. Boyle plants. This may allow tracing and measuring root lengths to be another (alternative) method to measure root systems. Planted rhizometers also allowed easy access for viewing the root system non-destructively, providing the ability to observe and measure root growth.

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William C. Fonteno, Matthew S. Drzal, and D. Keith Cassel

The influence of substrate physical properties on water transport and plant growth must be known if irrigation water use efficiency is to be improved. Three fundamentally different substrates were examined: 1 peat moss: 1 vermiculite (v/v), 3 pine bark: 1 peat: 1 sand, and 1 mineral soil: 1 peat: 1 sand. Capacity analyses included total porosity, container capacity, air space, available water and unavailable water. Water transport was characterized by saturated and unsaturated flow analyses. A new method, Pore Fraction Analysis, was developed to characterize substrate pore structure into fractions based on function with the substrate. This method is based on soil moisture retention curves, pore size distributions, and average effective suction at container capacity (AEScc) This method is offered to expand the traditional terms of macropore and micropore into new definitions: macropores, mesopores, micropore, and ultramicropore; each based on a range of pore sizes and functions. Computer simulation models of air and water profiles were run on several container sizes with the three test substrates. Pore fraction analysis indicated that under traditional production practices macropores indicate the volume of a substrate that be filled with air at container capacity, the mesopore fraction effectively fills and drains with daily irrigation, the micropore fraction functions as a measure of water reserve, while the ultramicropores contain water unavailable to the plant.

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James E. Altland, James S. Owen Jr, and William C. Fonteno

Moisture characteristic curves (MCC) relate the water content in a substrate to the matric potential at a given tension or height. These curves are useful for comparing the water-holding characteristics of two or more soils or soilless substrates. Most techniques for developing MCC are not well suited for measuring low tensions (0 to 100 cm H2O) in coarse substrates used in container nursery production such as those composed of bark. The objectives of this research were to compare an inexpensive modified long column method with an established method for creating low-tension MCCs and then to determine the best model for describing MCCs of bark-based soilless substrates. Three substrates composed of douglas fir (Pseudotsuga menziesii) bark alone or mixed with either peatmoss or pumice were used to compare models. Both methods described differences among the three substrates, although MCC for each method differed within a substrate type. A four-parameter log-logistic function was determined to be the simplest and most explanatory model for describing MCC of bark-based substrates.

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Todd J. Cavins, Brian E. Whipker, and William C. Fonteno

Most commercial and university substrate testing laboratories' recommended floriculture nutritional values are based on the saturated media extract (SME) method. With the recent gain in popularity of pour-through nutritional monitoring, alternative recommended values are needed for nutrient analyses based on pour-through extracts. Pour-through nutritional values were compared to the SME values to develop calibration curves and recommended nutritional values. Euphorbia pulcherrima `Freedom Red' Willd. ex Klotzch. were grown for two consecutive growing seasons in 16.5 cm plastic pots with Fafard 4 P root substrate and fertigated with 200, 300, or 400 mg·L-1 N from a 13N-0.88P-10.8K fertilizer. Linear relationships existed and inverse calibration curves for pour-through and SME comparisons were developed for (r 2): EC (0.98), NO3 - (0.98), P (0.97 to 0.99), K (0.99), Ca (0.94 to 0.97), and Mg (0.91). In addition, recommended pour-through substrate value ranges were developed for comparison with SME values. The established calibration curves and pour-through substrate value ranges will allow substrate-testing laboratories to make nutritional recommendations based on pour-through extractions.

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Jeb S. Fields, William C. Fonteno, and Brian E. Jackson

Wettability is a major factor in determining whether a material can be effectively and efficiently used as a component in greenhouse substrates. Poor wettability can lead to poor plant growth and development as well as water use inefficiency. This research was designed to test the wettability and hydration efficiency of both traditional and alternative components of substrates under different initial moisture contents (MCs) and wetting agent levels. Peatmoss, perlite, coconut coir, pine bark, and two differently manufactured pine tree substrate components (pine wood chips and shredded pine wood) were tested at 50% and 25% initial MC (by weight). The objective of this research was to determine the effects of initial MC and wetting agent rates on the wettability and hydration efficiency of these substrate components. Each component received four wetting agent treatments: high (348 mL·m−3), medium (232 mL·m−3), low (116 mL·m−3), and none (0 mL·m−3). Hydration efficiency was influenced by initial MC, wetting agent rate, and inherent hydrophobic properties of the materials. Wetting agents did increase the hydration efficiencies of the substrate components, although not always enough to overcome all cases of hydrophobicity.

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Rebecca L. Turk, Helen T. Kraus, Ted E. Bilderback, William F. Hunt, and William C. Fonteno

Twelve rain gardens were constructed to analyze the effectiveness of three different filter bed substrates to support plant growth and remove nutrients from urban stormwater runoff. The filter bed substrates included a sand-based substrate (sand) composed of (v/v/v) of 80% washed sand, 15% clay and silt fines, and 5% pine bark; a soil-based substrate (soil) composed of (v/v) 50% sandy loam soil and 50% pine bark; and a slate-based substrate (slate) composed of (v/v) 80% expanded slate and 20% pine bark. Coarse particles (6.3 to 2.0 mm) in the soil-based substrate created a large-pore network that conducted stormwater more quickly into and through the rain garden than slate or sand as evidenced by the high infiltration and saturated hydraulic conductivity values. Sand had good overall retention of pollutants except nitrogen (N) possibly as a result of the very small percentage (5%) of organic matter and low cation exchange capacity (CEC). Soil had the lowest remediation of phosphorus (P) and highest concentration of P in its effluent and was similar in N removal efficiency to slate. Slate had the best retention of N and P. Overall, all three substrates functioned in reducing the quantity of pollutants in urban stormwater runoff; yet, the impact of substrate on remediation appeared to lessen by Season 2 because there were few differences between substrate in the effluent nutrient concentration. Substrate did not affect shoot or root growth. Eleven of the 16 species (B. nigra, B. ‘Duraheat’, M. virginiana, M. ‘Sweet Thing’, I. virginica, I. ‘Henry’s Garnet’, J. effusus, P. ‘Shenandoah’, H. angustifolius, H. ‘First Light’, and E. purpureum subsp. maculatum) grew well in the rain gardens and could be used as rain garden plants.

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Jin-Sheng Huang, Paul V. Nelson, Douglas A. Bailey, William C. Fonteno, and Nancy C. Mingis

Salinity guidelines for seed germination substrates call for low, difficult to attain levels. This study was conducted to determine the value of N, P, K, and S as preplant nutrients, with the anticipation that some could be eliminated to alleviate the high salinity problem in many substrates. Impatiens wallerana L. `Accent Rose' and Gomphrena globosa L. `Buddy' were tested in 288-cell plug trays containing a substrate of 3 sphagnum peat moss: 1 perlite (v/v) in two experiments. Seven preplant N, P, K, and S treatments, including none, all (each at 100 mg·L-1 of substrate), all minus one of each of the nutrients, and N at one additional rate of 50 mg·L-1, were tested. Postplant fertilization was applied to all treatments as 13 N-0.9P-10.8K at 50 mg·L-1 N beginning 1 week after sowing and was increased to 100 mg·L-1 N when the fourth true leaf appeared. The resultant seedlings were transplanted into 48-cell flats and grown into marketable stage for further evaluation. For maximum potential growth, N, P, K, and S were needed as preplant fertilizer. However, compact shoots, not maximum growth, are generally desired in commercial production. Thus, K and S can be omitted since their contribution to growth was only occasional and small. To further ensure a consistently desirable level of compactness, it was necessary to omit N or P or both in addition to K and S. Omission of N alone yielded the most desirable compact plant qualities, including suitable reduction in final seedling size. Omission of P alone yielded larger reductions in height and shoot dry weight of seedlings compared to N omission, and a delay of 2 to 4 days in flowering of bedding plants. Omission of the four nutrients, compared to -P, resulted in similar seedling growth reduction and bedding plant flower delay. Since N omission lowered the salt (electrical conductivity) level of substrate more than P omission and had no negative impact on subsequent bedding plant flowering compared to the other two treatments, N omission would be the more desirable of the three. However, N omission resulted in chlorotic seedlings, but these quickly turned green upon restoration of N. Omission of P or all four nutrients resulted in desirably deep green seedlings. Growth of gomphrena seedlings, a high-fertilizer requirement category of taxa, was suppressed when the preplant rate of N was 50 mg·L-1 compared to 100 mg·L-1, while growth of impatiens, a low-fertilizer requirement category of taxa, was essentially equivalent at these rates. Preplant additions of nutrients applied at 100 mg of nutrient element per liter of substrate lasted for the following numbers of days; NO3-N, 18-25 days; NH4-N, 12-20 days; K2O, 27 days; PO4-P, >35 days; and SO4-S, >35 days.