Horticultural Substrates Research Articles

Protocol to Quantify the Reactivity of Carbonate Limestone for Horticultural Substrates

The current method for comparing the reactivity of different limestones used to correct pH in horticultural substrates is based on batch trials, where the limestones are incorporated into the substrate and the pH is measured over time (typically up to 28 days). The objective was to test a laboratory approach to provide a rapid analytical test on reactivity of various limestone sources. To a lime sample, 4M hydrochloric acid (HCl) was added, and the volume of carbon dioxide (CO2) released into a burette was measured over time. Reagent‐grade calcium carbonate (CaCO3) and two commercially available pulverized dolomitic limestones were tested. In addition, six particle‐size fractions derived from each of the limestone samples were also evaluated for reaction rate and the corresponding pH responses. In less than 1 min after acid addition, 100% of CaCO3 reacted, whereas it took 3.9 and 11.5 min, respectively, for 50% of the limestone samples to react, and 14 and 52 min, respectively, for 90% neutralization. Reaction rate increased as the particle size decreased; however, a similar reaction rate was observed for the particle sizes larger than 150 µm (>100 U.S. mesh). Time to 90% reaction was negatively correlated with pH response when 6 g of each lime was incorporated per L of peat substrate. It may be possible to establish a lime reactivity index, for example based on the time required for 50% or 90% reaction, and thereby provide a rapid screening of different limestone sources.

(70) Improved Reactivity Indices for Horticultural Limes

The objective was to develop indices to describe reactivity of different lime particle size fractions with respect to pH change in horticultural substrates. Particle size efficiency (PSE) was calibrated from pH responses for separated six lime particle size fractions (>850, 850 to 250, 250 to 150, 150 to 75, 75 to 45, and <45 μm) from three calcitic limes, and seven dolomitic limes, based on their increase in substrate pH relative to reagent grade CaCO3 when mixed in a sphagnum peat substrate at 5 g CaCO3 equivalents per liter of peat. The fineness factor (FF) was calculated for a liming material by summing the percentages by weight in each of the six size fractions multiplied by the appropriate PSE. The effective calcium carbonate equivalence (ECC) of a limestone was the product of the FF and the acid neutralizing value (NV) in CaCO3 equivalents. Reliability of the parameters for FF and ECC were then validated in two experiments, using 29 unscreened carbonate and hydrated lime sources, including the 10 calibration limes. In one experiment, 1 L of peat was blended at 5 g of lime (i.e., not corrected for differences in NV between limes). In the second experiment, 5 g CaCO3 equivalents for each lime, corrected for NV, were blended with 1 L of peat (a different peat source), using the same 29 lime sources. Both FF and ECC were positively correlated with the corresponding substrate-pH changes, with P < 0.001 and r2 from 0.87 to 0.93. This calibration of PSE, FF, and ECC can improve limestone selection and application rate for the short term response and fine limestone sources used in horticulture.

(66) Modeling Lime Reaction in Horticultural Substrates

Limestone is incorporated into horticultural substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual”? lime. In horticulture, lime reactivity is currently measured empirically in batch tests, whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

OPTIMALIZATION OF OXYGEN LEVELS IN ROOT SYSTEMS AS EFFECTIVE CULTIVATION TOOL

OPTIMALIZATION OF OXYGEN LEVELS IN ROOT SYSTEMS AS EFFECTIVE CULTIVATION TOOL

Effect of physical properties of horticultural substrates on pepper transplant development

Pepper transplants were grown in trays using 6 different growing media. Trays were filled in a loose and in a compact manner with the 5 different peats and coconut coir. Measurements were made for the most important physical parameters of each single medium studying their effect on transplant development. Results indicated that compaction had had a beneficial effect on the germination of the transplants and on the rate of their development.

A Protocol to Quantify the Reactivity of Carbonate Lime for Horticultural Substrates

Lime sources vary in their reactivity depending on particle size, surface area and crystalline structure, and chemical composition. Current horticultural practice for testing lime reactivity and the appropriate lime rate is through batch trials where lime is incorporated into growing media. Our objective was to test a laboratory approach that would provide a rapid analytical test on reactivity of lime sources, and could eventually be applied to measuring unreacted (residual) lime in container media. Four moles HCl was added to a lime sample, and the volume of CO2 released over time was measured in a burette. Three lime types were tested, including reagent grade CaCO3, and two pulverized dolomitic limestones used in horticultural media. 100% of CaCO3 reacted in less than a minute after acid addition, whereas only 79.8% and 49.5% of the two commercial lime samples had reacted after 10 minutes. The time required for 50% of the two commercial lime samples to react was 5 and 10 minutes, respectively, whereas it took 20 and 60 minutes, respectively, for 95% neutralization. Reaction rates in the laboratory test correlated with the time required to achieve a stable pH level when limes were incorporated into a peat substrate. The reagent-grade CaCO3 raised pH more rapidly (within 7 days) and to a higher level (maximum pH 7.5 at 9 g of lime per liter of peat) compared with the dolomitic lime sources. It may be possible to establish a lime reactivity index, for example, based on CO2 release after 10 minutes, and thereby provide a rapid screening of limes. Further gasometric analysis of lime types used in horticultural substrates is therefore needed.

Measuring Hysteretic Hydraulic Properties of Peat and Pine Bark using a Transient Method

The precise and continuous measurement of the hydraulic properties of growing media is of vital importance for the effective management of irrigation and fertilization. The main purpose of this study was to use a transient method to characterize the hydraulic properties of two horticultural substrates (peat and composted pine bark) and, second, to test the applicability of well-known hydraulic models commonly used on mineral soils. Substrate water retention and hydraulic conductivity curves were determined in the laboratory by the Instantaneous Profile Method (IPM), during a drying–wetting cycle. The results showed hysteresis for peat in the θ(ψ) curves (30% vol.) and in the K(ψ) curves [one order of magnitude in K(ψ)], whereas this phenomenon was very limited for pine bark [approximately 10% vol. in θ(ψ) and approximately a half-order of magnitude in K(ψ)]. The K(θ) curves for both substrates considerably decreased after the considerable variation in water content observed in θ(ψ), that is to say, after −5 and −3 kPa for peat and pine bark, respectively. Fitting the van Genuchten retention model to observed data resulted in a high correlation (0.96 ≤ R2 ≤ 0.99) and fitting unsaturated hydraulic conductivity models (VGM and BC) resulted in a lower correlation (0.43 ≤ R2 ≤ 0.64). Our results seemed to be in agreement with other hydraulic studies of substrates. These overall results implied that hydraulic properties of tested substrates widely fluctuate in a narrow range of water potentials that could therefore rapidly affect water and air availability to the roots. Knowledge of K(ψ) and K(θ) curves, in addition to the θ(ψ) curve, could contribute to alleviating stress conditions.

Micropropagation du Chêne-liège (Quercus suber L.) par culture d'apex issus d'axes embryonnaires

To improve the in vitro germination and development of cork oak embryonic axes, several mineral media were tested; Durzan medium modified 1/2 supplemented with 400 mg/l glutamine and 3% sucrose gave the best results. The action of BA alone or combined with other growth regulators was also studied. A low concentration (0.44 μM) was found to give an acceptable percentage of plantlets. When combined with NAA, callogenesis was observed. The transfer of cultures in conditions of low luminosity led to the formation of several axillary buds. These buds were multiplied on a solid medium supplemented with GA3 at low concentration. The buds were elongated, then rooted on a growth regulator-free medium after brief dipping in an auxinic solution. The rooted plants were potted on horticultural substrate.

Micropropagation du Chêne-liège (Quercus suber L.) par bourgeonnement axillaire

The in vitro regeneration from cork oak axillary buds was investigated. Different macronutrient formulas supplemented with MS micronutrients, vitamins and 3% sucrose were tested on shoot multiplication and rooting phases. The WPM macronutrients improved caulogenesis and shoot multiplication. Rooting was achieved on WPM 1/2 macronutrients. Dipping the base of the shoots in an IBA concentrated solution improved the rooting phase. 92% of the rooted plants were successfully potted on horticultural substrate with a high relative humidity.

Variability of Soluble Salts Using Different Extraction Methods on Composts And Other Substrates

Soluble salts represent dissolved inorganic ions in solution and are typically measured in terms of electrical conductivity (EC). Often soluble salt measurements from different studies or laboratories cannot be cross-referenced or there is much confusion when comparing these results. The soluble salts from 13 composts and horticultural substrate materials were extracted using six different methods: saturated medium extract; pour-through, a water displacement method; and water suspensions using various ratios (by volume) of water:substrate (1:1, 1:2, 2;1, 5:1). EC ranged from 0.1 (peat and perlite) to 23.1 dS m−1 (turkey litter compost). A linear regression model was developed to allow cross-referencing between extraction methods of measurements of soluble salts concentration of the composts and substrates.

Ground Bovine Bone as a Perlite Alternative in Horticultural Substrates

Two grades of ground bovine bone were evaluated as potential alternatives to perlite in horticultural substrates. The bulk density of small and large bone-amended substrates was significantly higher than equivalent perlite-amended substrates. Large and small bone increased the air-filled pore space of sphagnum peat. However, at 10% and 20% (v/v), neither size of bone resulted in as high an air-filled pore space as equivalent amounts of perlite. At 30% and 40%, incorporation of small bone resulted in a similar air-filled pore space as incorporation of equivalent amounts of perlite, and incorporation of large bone resulted in a higher air-filled pore space than incorporation of equivalent amounts of perlite. Water-filled pore space and water-holding capacities of substrates were inversely related to air-filled pore space. When placed in a moist substrate, mineral elements within the bone were able to leach into the substrate over time. Substrates amended with 40% large and small bone had significantly higher concentrations of ammonium (NH4+), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), and chloride (Cl-) than the 40% perlite-containing substrates. Substrates amended with 40% large bone had similar concentrations of magnesium (Mg), sulfur (S), iron (Fe), and copper (Cu) while substrates amended with 40% small bone had higher levels of these elements than perlite-amended substrates. Substrate concentrations of nitrate (NO3-), manganese (Mn), zinc (Zn), and boron (B) were not different among the substrates after 4 weeks in the greenhouse. The pH, electrical conductivity (EC) and NH4+ levels of bone-amended substrates increased to levels significantly higher than recommended and resulted in rapid mortality of `Orbit Cardinal' geranium (Pelargonium × hortorum), `Cooler Blush' vinca (Catharanthus roseus), and `Dazzler Rose Star' impatiens (Impatiens walleriana) plants grown in bone-amended substrates. Therefore, ground bovine bone was not a feasible alternative to perlite for use in horticultural substrates.

Bulk density and relationship air/water of horticultural substrate

Change on substrate bulk density during the growing period may negatively affect other substrate physical properties and, consequently, plant growth. The objectives of this research were 1) to characterize physical properties of two horticultural substrates (S1 and S2), 2) to evaluate the effect of different bulk densities values of those substrates on their air/water relationship, and 3) to develop mathematical functions to estimate the air/water relationship by increasing substrates bulk density value. First, the distribution of particles size, the bulk density, and the water release curve of the substrates were determined. Then, substrates were packed with three different bulk density values, i.e. 10% (D1), 20% (D2) and 30% (D3), higher than the bulk density (D) determined in the characterization phase. The water release curves were determined for each bulk density value of both substrates. The effect of increasing substrate bulk density in the total porosity (TP), aeration space (AS), available water (AW), easily available water (EAW), buffering water (BW), and in the remaining water (RW) was evaluated using simple linear regression and polynomial analysis. The particles size distribution and the water release curves were significantly different for the two substrates. Increasing the bulk density value decreased TP and AS, and increased BW and RW. The highest values of AW and EAW were observed for D1. Regression equations obtained can be used to choose the more appropriate air/water relationship for each growing condition.

Inoculation ofRhododendron cv. Belle-Heller with two strains ofPhialocephala fortinii in two different substrates

The growth response of an ornamentalRhododendron hybrid to the inoculation withPhialocephala fortinii was studied in two pot experiments in order to decide about the effectiveness of the inoculation of young rhododendron microplants. Two different substrates were used in both experiments, either sterilized or non-sterilized: a horticultural substrate and a soil collected from a field site with dominant ericoid vegetation. Two fungal isolates were used for an inoculation:P. fortinii strain P (UAMH 8433) andP. fortinii strain F, a dark septate endophyte (DSE) previously isolated from naturally-infected roots ofVaccinium myrtillus. BothPhialocephala strains successfully colonized the roots of the host plants forming typical DSE (=pseudomycorrhizal) colonization pattern including the formation of intracellular microsclerotia. However, pseudomycorrhizal colonization did not affect the growth parameters of the host rhododendrons. The results from both experiments indicate a neutral effect of the inoculation with DSE fungi on the growth ofRhododendron cv. Belle-Heller.

New technologies and improvement of nursery stock quality

This four years experimentation work was aimed at research on using various waste organic materials and especially timber bark in cultivation substrates as a substitute of peat. Sixty-four special isolated cultivation beds were established for this purpose, each of 4.8 m<sup>3</sup> volume, in which 11 variants of substrates consisting of different proportions of different components in several replications were tested. Standard substrates Horticultural substrate B and RKS I. were used as controls. Another variant was used as a control for growing tests of plants in containers. All tested substrates were enriched with hydroabsorbent TerraCottem. In some variants reserve fertilisers with slow release of nutrients (Silvamix Forte) were applied. For cultivation testing of studied substrates four ornamental tree species (Alnus glutinosa, Fraxinus excelsior, Salix alba, Salix matsudana) were chosen. The best evaluated variants were the ones containing 50 and 75% of bark in combination with sand. The worst was the variant composed of chips and sawdust. Thanks to the use of hydroabsorbents, even the variant containing 100% of sand appeared to be very good. The tested trees had different reactions to the different types of substrates depending on their species requirements. The limiting growth factor for Alnus was the content of water in the substrate. Similarly, the content of available nutrients in the substrate was essential for Fraxinus. The hardwood cuttings of Salix not only rooted into the substrate in a few weeks, but also formed aboveground parts of the required sizes. Obtained data on growth parameters differed according to the diversity of requirements of the different studied species.

Inoculation of cyclamen (Cyclamen persicum) and poinsettia (Euphorbia pulcherrima) with arbuscular mycorrhizal fungi and Trichoderma harzianum

Dual inoculation of peat based horticulture substrate with a mixture of four species of arbuscular mycorrhizal fungi and fungal biocontrol agent Trichoderma harzianum showed a significant positive effect on the growth and flowering of cyclamen plants. Inoculation substantially decreased plant mortality caused by spontaneous infection by the fungal pathogen Cryptocline cyclaminis. Plant mortality was also reduced by separate inoculation with arbuscular mycorrhizal fungi. Both separately inoculated agents positively affected the plant growth, although to a lesser extent. Very few significant effects of inoculation were observed on the growth of poinsettia plants cultivated from cuttings. Use of arbuscular mycorrhizal fungi together with the introduction of Trichoderma for inoculation of horticultural substrates is suggested to alleviate the inevitable effects of various stresses during the cultivation of horticultural crops.

Substitution von Torf durch Holz in Pflanzsubstraten

The chemical and physical properties of three softwood species were investigated to develop a plant substrate from wood and wood fibres in a mixture with compost and to substitute peat in horticultural substrates.

262 Standard Time Domain Reflectometry Curves for Cyclic Irrigation Management in Container Production

The physical properties of soilless substrates used in the nursery industry vary widely throughout the US, and, as such, present problems for accurate irrigation water management. Water management in soilless substrates is also a key factor in reducing the loss of soluble nitrogen and phosphorus from the root volume. Automated irrigation control that maintains the substrate water content above levels of plant water stress, yet below the maximum water holding capacity of the substrate will serve several positive roles: water and nutrients will be conserved, and losses from run-off minimized. We investigated whether Time Domain Reflectrometry (TDR) moisture sensors can be effectively calibrated for a range of horticultural substrates in various container sizes. A series of water desorption curves and TDR wave-traces (n = 10) were simultaneously derived for six soilless substrate source materials (pine bark, hardwood bark, promix, perlite, rockwool and a sieved sand control), using a modified tension table with four column heights (7-, 15-, 20-, and 25-cm equating to rockwool, #1, #3, and #5 pot sizes). Modifying the tension table allowed for the replication of individual columns (n = 10) of each substrate. The volumetric water desorbed at increasing desorption (positive air) pressures from 0 through 100 KPa was collected for each treatment. Repeated measurements with this apparatus allowed us to plot standard TDR curves for each substrate that can be used to accurately schedule cyclic irrigations. Implementing automated cyclic irrigation strategies in container production will allow for better monitoring and control of irrigation applications, and help conserve water and nutrients in the nursery.

BIODEGRADED COCOPEAT AS A HORTICULTURAL SUBSTRATE

Cocopeat or coir dust is a by-product separated during processing of coconut (Cocos nucifera L.) coir. As a by-product of coir manufacturing, cocopeat is often unutilized or burnt in the open. Of late, due to environmental concerns and also diminishing supplies of peat soils for horticultural substrates, cocopeat is being considered as a renewable peat substitute for use in horticulture. However, in its raw form, cocopeat has been reported to contain phytotoxic elements which inhibit plant growth. As such, cocopeat is often recommended for use only with a mixture of other organic or inert materials. The present study was conducted to determine the effect of biodegradation (composting) on improving the qualities of cocopeat as a horticultural substrate. Cocopeat was supplemented with 0.75% N and inoculated with selected mould and wood rotting micro-fungi viz. Aspergillus niger van Tieghem, Penicillium citrinum Thom, Trichoderma sp., Humicola sp. and Chaetomium globosum Kunze. The medium was maintained at about 80% moisture content (wet weight basis) and incubated at 27°C for 3 months. The results showed that the 3-month biodegraded cocopeat has lower C/N ratio, higher CEC and humic acid than the raw cocopeat. The lowering of C/N ratio was due to addition of N and the reduction of carbon, mainly the hemicellulose, cellulose and to a lesser extent the lignin components. In the greenhouse trial, tomato plants grew well in the 3-month 'composted' cocopeat. Though their plant heights and stem diameters were not significantly different from those grown in the untreated cocopeat, the plants on 'composted' cocopeat produced higher dry root weights (22%), fruit numbers (43%) and total yield (64%).

Micropropagation of the Mediterranean species Viburnum tinus

In vitro propagation of the Mediterranean species Viburnum tinus L. was established from an outdoor-grown shrub. Two standard macrosalt formulations (Margara N30K and Murashige and Skoog), a range of benzyladenine and sucrose concentrations were tested for their effect on shoot multiplication. The cytokinin concentration was the most important factor affecting shoot multiplication. The highest shoot multiplication rate was obtained from single-node explants cultured on Murashige and Skoog medium supplemented with 4.4 μM benzyladenine. Cytokinin concentration and an interaction of macrosalts and benzyladenine influenced shoot length on the multiplication stage: best shoot growth was observed on MS medium containing 1.1 μM benzyladenine. In addition, sucrose concentrations of 87.6–146.0 mM gave the highest multiplication rates and improved shoot growth. Following a shoot ellongation stage, single shoots were rooted on media containing naphtaleneacetic acid (1.3–5.4 μM). Although enhanced in vitro rooting was obtained on media containing 5.4 μM naphtaleneacetic acid, reducing the auxin concentration to 1.3 μM during the in vitro rooting stage improved acclimatisation frequency and further plant growth in a horticultural substrate.

Measuring Water Content of Soil Substitutes with Time-domain Reflectometry (TDR)

Optimization of irrigation and fertilization regimes in greenhouses and other controlled environments requires accurate and frequent measurements of soil-water content. Recent studies on TDR use in gravely soils and in closed-container studies have indicated a potential use of this method in horticulture. In this study, TDR calibration curves were determined for tuff (granulated volcanic ash), vermiculite, perlite and a mix of two composted agricultural wastes (grape marc, separated cow manure). Widely used as horticultural substrates, mixes of these materials were tested as well. For all soil substitutes tested, measured calibration results are well described by linear equations throughout tested values of water content that cover the working range in horticulture. Ledieu's equation, widely used in soils, describes fairly well the measured results for perlite, but underestimates those obtained for organic media, vermiculite (because of the presence of bound water) and tuff (probably due to water in occluded pores). The differences obtained between the measured calibration equations and Ledieu's equation indicate that in order to avoid an erroneous irrigation management, calibration is necessary whenever a new soil substitute is used.