Temperature and salinity effects on measurements of growing media moisture content carried out with TDR and capacitance probes.

摘要

The irrigation of pot crops requires considerable monitoring because the autonomy of the water reserve of the growing media is low in relation to plant water requirements. Computerized systems for irrigation management are therefore under investigation at this time. Time Domain Reflectrometry (TDR) is used to directly measure the water content of a soil. For growing media, the relationship between the dielectric constant Ka and the water content is valid provided that the calibration equation, generally polynomial, is established for each medium. Thus, the practical use of this equipment in horticulture can be proposed, but its high cost remains a major obstacle. That is why we are looking for other less expensive alternatives that work on a similar principle. Two types of material (TDR and ECH2O capacitance probe) were tested at four different water potentials (-1, -5, -10 and -20 kPa), in two growing media (peat/perlite and peat/bark mixtures). In order to check their reliability under different operating conditions, measurements were carried out at two average temperatures (14.1 and 24.5 degrees C) and at three increasing salinities; the growing medium was moistened with a solution containing 0.1 and 2 g/L of soluble fertilizer. The results showed the non-sensitivity of TDR under environmental conditions, except to the growing medium composition, and the high sensitivity of ECH2O probes to salinity. This material also requires an individual calibration of each probe, but is not sensitive to the temperature and to the type of growing medium. It is also much less expensive than TDR.