Location: Application Technology Research Unit
2012 Annual Report
1)and alkalinity in irrigation water (Factor.
2)currently exists. Our project focuses on how to better quantify the effects of the remaining three factors. In order to quantify the three remaining factors it is necessary to develop titration curves for the root substrates under study. The titration curve offers a rapid tool for quantifying the amount of acidity that is gained or lost under the influence of the tested factors that cause pH shift during cultivation. The current, alternative procedure for measuring acidity shift is the substrate incubation method which requires up to one week to run and provides an undesirably limited number of data points for research purposes. In an earlier phase of this project, titration curves were generated using automatic titrators. However, through subsequent test runs it was obvious that there were additional parameters that could be changed to improve the procedure. During the past year we evaluated these parameters to ensure that the final titration curve was reproducible, reduced hysteresis, and produced a curve that was as close to actual incubation data as possible. The eight parameters tested included titrating at fast, moderate, and slow rates (maximum 7.00, 2.00, and 0.33 mL acid/base per minute, respectively); fast rate with slowed addition near upper and lower pH endpoints; changing the forward titration endpoints from pH 11 to pH 8 for one or both cycles; and titrating at a moderate rate after shaking for 2 hours or 24 hours at approximately pH 11. Reducing the speed of acid and base titrant addition improved the titration outcome, but it was possible to achieve the same result with a great savings in time by using the fast addition combined with proportional slowing of the addition as the two pH end points of 11 and 3 were approached. Results were further improved by shaking the mixture for two hours when the first pH 11 end point was reached. Shaking for 24 hours instead of only 2 at this point added little improvement. The final procedure calls for hydrating 1.5 grams of equivalent dry peat moss in 50 mL of de-ionized water by raising it from its ambient pH of around 3.5 to 11, holding it at pH 11 while stirring for two hours, then lowering the pH to 3. Titration then proceeds by addition of 0.1 M sodium hydroxide base to raise the pH to 11 followed by 0.1 M hydrochloric acid to lower pH back to 3. The rate of addition of titrants is 7 mL per minute except at the pH 11 and 3 end points where the rate is lowered in proportion to how close one is to the pH end points. The results of this work benefit two audiences. The first is the scientific community who can use the titration technique as a method for precisely measuring acidity changes in root substrate as a consequence of experimental treatments. The second audience is comprised of larger greenhouses and nurseries who mix their own root substrate and the substrate formulation companies who supply substrate to container plant production firms. This will give them a rapid method for assessing the limestone requirements of successive batches of root substrate as they are being prepared for commercial use. This project relates to sub-objective 3a of the parent project: Evaluate existing and alternative growth medium components to determine the potential benefit of individual components on production efficiency, transportability, and shelf life of ornamental crop. It assists with milestones at 60 months: Complete comparative studies of promising substrates that enhance media growth characteristics.