ISHS Acta Horticulturae 401: International Symposium on Growing Media & Plant Nutrition in Horticulture
A METHOD FOR EVALUATION OF AIR VOLUMES IN SUBSTRATES |
| Authors: | V. Terés, V. Arrieta, M. Rozas |
| Keywords: | physical characterization, pycnometry, error evaluation |
| DOI: | 10.17660/ActaHortic.1995.401.3 |
| Abstract:
The physical characterization of substrates is important to provide criteria to establish irrigation management of crops. The difficulty of obtaining direct measurements of the volume of air makes that it has to be determined indirectly. This causes accumulation of errors. The objective of this work is the development of a methodology to measure the volume occupied by air that avoids the accumulation of errors and allows the measurement of the global accuracy of the individual measurements. Very fine composted pine bark and perlite were used to test the different methodologies. Samples were saturated by boiling and were put on a sand bed. The influence of losses of material and the associated errors were determined. The volumes of solid material, and solid material plus water were directly obtained following the Archimedes principle. Global error evaluation was carried out by taking the difference between total volume and the sum of solid, water and air volumes. The global accuracy of the method was good and errors in pine bark ranged from -0.1 to 0.5%. In this substrate the values obtained for the volume occupied by air were negative and the correction of solid losses during boiling is important as the volume occupied by air increased from -6.38 to -3.76 cm3. The confidence interval for  = 0.05 does not include the reference value of Vai, which is zero.
Therefore, in this work there must be other sources of error which were not studied such as a poor estimation of the total volume of the sample.
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