Mobile-Immobile Phase in Different Growing Media for Greenhouse Tomato Production.

In sustainable development, many recent studies have promoted organic substrates such as peat and sawdust mixtures as sustainable substrates in greenhouse tomato production. However, electrical conductivity tend to rise in these substrate, due possibly to the irrigation management, or to the growing media properties, among which the existence of a significant immobile fractional water in these media. Two of the main parameters of the MIM, the immobile water fraction (θ_im) and the mass exchange coefficient between the mobile and immobile phases (α) were determined through a steady state leaching experiment in substrates columns combined with parametric fitting of an analytical solution to the MIM. Results were compared to leaching studies on used substrates. Results appear contradictory. Results on the leaching of new substrates suggested little virtually no immobile water content while the leaching of used substrates suggested a very significant proportion of immobile water.  Reasons for discrepancy seem linked to the solute sorption process itself. Possible mechanisms will be presented.