USE OF COMPOSTED CORK AS A NURSERY SUBSTRATE FOR LETTUCE

Composted cork (C) as a growing medium component in plug seedlings production of lettuce (Lactuca sativa L.) was studied. C was used both pure and mixed with a commercial substrate of Sphagnum peat moss (P), in proportions of 1:1 (v:v) and 1:2 (v:v). P was considered as control. Before testing with plants, physical and chemical properties were determined in C, P and their mixtures. Bioassays were carried out for detection of phytotoxicity, calculating the germination indexes (GI) in C and P, and the nitrogen drawdown index (NDI) was also determined. Treatments were arranged in a randomized block design with 4 replications, each experimental plot had 50 cells. Tests were conducted in a greenhouse, in Seville, during spring 2007, watering 5 days a week with a Hoagland solution. C had a neutral pH, low salinity and lack of phytotoxicity, but it had high capacity for N immobilization and smaller easily available water than P. Plants grown in C had lower dry weight, less height, a smaller number of leaves, less leaf width and a smaller diameter in the root neck, than plants grown in P. The delay in growth decreased as the proportion of C in the mixture increased. There were no significant differences in germination, mean germination time and the chlorophyll content measured with SPAD. Significant differences were also found in the nutrient contents in the aerial part of lettuce seedlings.