ISHS Acta Horticulturae 779: International Symposium on Growing Media
DEVELOPMENT OF MODELS FOR PREDICTING THE PH EQUILIBRIUM OF ORGANIC SUBSTRATES |
| Authors: | R. Nemati, J.P. Fortin |
| Keywords: | lime requirement, soilless mixes, buffer solutions, 0.01 M CaCl2, 0.1 M CaCl2, 1 M KCl, SMP single-buffer, double buffer SMP, pH in DD water |
| Abstract:
Several components used for manufacturing organic soil mixes have a natural acidic pH (pH 3.0 to 4.5) and require the addition of lime for neutralization. Since the process of neutralization requires the displacement of exchangeable cations, the neutralization period may take several weeks to obtain a pH at equilibrium (pHw(e)). The purpose of this study was to develop a rapid and accurate method of measurement which will permit the anticipation of the pHw(e) of organic substrates directly from instant pH measurements. The study also aims to evaluate the role of various ingredients on pHw(e) and to study their interactions in order to develop a model to determine lime requirements for the pH targeted. The research was conducted and the models were developed following a method of enlighten experimentations using multivariate analyses (EM Optimization inc., Montreal, Qc). A total of 34 substrates were selected to initiate the experiment. Several methods to determine the instant pH were tested such as 0.01 M CaCl2, 0.1 M CaCl2, 1 M KCl, SMP single-buffer, double buffer SMP and pH in DD water (1:1, vol/vol). The substrates were put under cultivation until pHw(e) was obtained. Several models were developed to determine the relationship between instant pH and pHw(e) and to determine the lime requirements in organic substrates. Validation experiments were then conducted to evaluate the efficiency of the models. The correlation coefficient between predicted and measured pHw(e) values were 0.90 for the model obtained from pH measurements in DD water, and 0.87 for the model obtained from pH measurements in 0.01 M CaCl2. A very close correlation (R2=0.86) was also observed between the predicted lime requirement (LR) and the real amount of lime used when using the model of LR determination. | |
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