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  • Author or Editor: Maria Bakea x
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The residues of the aquatic plant Posidonia oceanica that are washed ashore, thereby causing environmental problems in coastal areas, can be used as growing media in horticulture. In the present study, the hydraulic characteristics of raw or composted Posidonia residues, coir, and their 1:1 blends (v/v) with pumice were determined, and their agronomic performance was evaluated in a lettuce crop. The mixture of all three substrates with pumice reduced their effective pore space and increased their bulk density. Furthermore, the water and air capacity (determined at a suction of 10 cm) and the easily available water were also reduced by mixing the three tested media with pumice. The relative hydraulic conductivity (Kr ) decreased with increasing suction (ψ) in all of the tested media. The highest and the lowest rates of Kr decrease with increasing ψ were observed in the mix of non-composted Posidonia with pumice and in 100% composted Posidonia, respectively. Blending composted or non-composted Posidonia with pumice at a 1:1 ratio raised the rate of Kr decrease with increasing ψ in comparison with 100% composted or 100% non-composted Posidonia, respectively. In contrast, blending coir with pumice reduced the rate of Kr decrease with increasing ψ in comparison with 100% coir. The differences in the mean fresh weight between lettuce plants grown on the six growing media were similar with those in the rate of Kr decrease with increasing ψ. These results indicate that the crucial factor for the yield performance of lettuce grown on the tested growing media was not the air but the water availability. Furthermore, the present results indicate that the actual water availability to plants grown on the tested substrates depends much more on water flux toward roots and concomitantly on their hydraulic conductivity than on the easily available water (i.e., the difference in water content between 10 and 50 cm suction).

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