GROWING LAMB'S LETTUCE (VALERIANELLA OLITORIA L.) ON RECYCLED POLYURETHANE (PUR) HYDROPONIC MATS

A system was developed in which lamb's lettuce was sown on recycled polyurethane-ether (PUR)-mats with a thickness varying from 0,8 to 4,6 cm, which were laid out on tablets with a slope of 2,7%. On these tablets there was a flow of nutrient solution with a pH of 6 and a electric conductivity of about 1,4 mS/cm.

About the beginning of September the pre-germinated lamb's lettuce seed was laid out on the moist PUR-mats in rows with a distance of 10 cm between the rows.

The plants artificially illuminated at a rate of 150 W/m2 were ready for harvesting after about 60 days already; the plants without supplementary light had a growth delay of at least a fortnight.

Depending on the treatment the yield varied from 1,260 to 1,950 g per sq.m.

Mainly the irregular germination and development of the young seedlings need to be further improved.

Up till now the unsown areas were coverd with expanded polystyrene (ISOMO)-strips in order to slow down the development of algae as much as possible. However, this material proved to be insufficiently lightproof. Aluminium strips may provide a solution here.