Franklin A. Pokorny

Estimating shrinkage of container media mixtures with linear and/or regression models

Abstract Shrinkage occurs when container medium components of different particle sizes are mixed which poses a major problem in computer modeling of container media. We have devised a theoretical model, linear in nature, which requires shrinkage determination only at the 1: 1 v/v proportions and that predicts shrinkage in binary and ternary mixes. Therefore, it is simple, rapid and economical to use. Regression models were also utilized to characterize shrinkage estimation, but they require a large number of laboratory determinations to develop and are cumbersome to use in comparison to the theoretical model.

Container medium characterization by scanning electron microscopy and comparison with a Monte Carlo computer simulated medium

Abstract A 1:1 by volume pine bark and sand containermedium was embedded with Spurrs epoxy resin and cross‐sectioned for SEM characterization of particle distribution. A Monte Carlo computer simulated medium was built with spheres of the same particle size distribution as the pine bark and sand grains used in the experiment. Cross‐sections from the simulated systems were compared with actual experimental data and good agreement was obtained. SEM makes it possible to analyze particle and pore distribution of container media. Computer simulation provides a good approximation of container medium structure and may prove useful in estimating properties of container medium mixtures.

Prediction of water-retention of milled pine bark-sand potting media from laboratory analyses of individual components

Abstract A mathematical equation which estimates water‐retention of synthesized milled pine bark‐sand pottinq media from laboratory analyses of each medium component was formulated and tested. The equation is the weighted sum of water retained by each component at a specified tension level. Media samples were sequentially subjected to 0‐, 10‐, 50‐, and 100‐cm water tension for 72 hours. Regression equations describing measured and estimated water retention at each pressure level increased linearly with increasing volumetric percent bark. The two regression equations corresponding to each tension level were not statistically different indicating that the equation for estimating water retention is reliable with synthesized pine bark‐sand media.

Prediction of H-ion activity of two-component potting media from analysis of components

Abstract A mathematical equation which predicts H‐ion activity (HA) of container media from laboratory analysis of components was devised and tested. The equation is based on the weighted sum of HA contributed by each component. Both measured and predicted HA increased linearly with increasing volume percent bark in milled pine bark‐sand media. Regression equations describing measured and predicted HA were not statistically different. The predictive equation was also tested on other 2‐component potting mixtures with no statistical differences occurring between measured and predicted HA. Measured pH and pH values derived from the HA predictive equation were in close agreement.

Electron microprobe analysis of calcium solution penetration into milled pine bark particles

Abstract Pine bark (Pinus taeda L. and P. elliottii Engelm.) pieces, 2.5 to 5.0 cm diameter, submerged in water became saturated more rapidly in a vacuum than at atmospheric pressure. A test was conducted to determine the extent of Ca solution penetration into smaller milled particles and the effect physical structure of particles has on this process. Particles 2.0–2.8 mm diameter were submerged in a solution of 1000 ppm Ca as Ca(OH)2, placed in desiccators and evacuated to 150 mm Hg of tension. At intervals of 24, 48 and 96 hours samples were removed, freeze‐dried, and cut tangentially to expose the internal phloem. Electron microprobe x‐ray analysis initially showed different Ca concentration in peripheral and central zones and indicated that Ca solution had penetrated the particle and saturation was completed within 96 hours. The progression of Ca penetration was uniform from all edges and indicated that the varied structure of bark tissues did not impede water penetration.

Determination of nitrate in a pine bark substrate

Abstract An experiment was conducted to evaluate extraction methods for the determination of nitrate in a synthesized pine bark substrate. It was found that prior to nitrate determination, oven dryino of the pine bark sample was necessary followed by rewetting and extraction in a vacuum for 72 hours. Using this technique, about 65% of applied nitrate was recovered.

Cation exchange capacity of two‐component container media predicted from laboratory analysis of components

Abstract A mathematical equation predicting cation exchange capacity (CEC) of pine bark‐sand container media from CEC of the individual components was formulated. The equation is the weighted sum of milliequivalents contributed by each component and is corrected for shrinkage due to mixing of components. Both measured and predicted CEC increased linearly with increasing percent volumetric bark in pine bark‐sand media. Regression equations describing measured and predicted CEC were not statistically different. The predictive equation was also tested on 6 non‐synthesized 2‐component media prepared from peat moss, perlite, pine bark, vermiculite, and sand. No statistical differences between measured and predicted CEC were obtained.