GRAPE MARC AND PINE BARK COMPOSTS IN SOILLESS CULTURE

     Grape marc and pine bark were composted in windrows for a period of three months, supplied with 1kg of nitrogen (urea) m^-3. Grape marc compost (GMC) and pine bark compost (PBC) had, respectively, 84.3 and 85.0% v/v total pore space, 10.3 and 1.2 % v/v easily available water, 59% and 32.0% v/v air capacity, 53.0 and 25.9 % v/v total water content. Rockwool (Grodan^®) has higher total pore space (96.7% v/v) and total water content (81.8% v/v) but lower air capacity (14.9% v/v). Rockwool, GMC and PBC were compared as plant substrates for growing a greenhouse tomato crop. Plants of tomato 'Sinatra' (Sluis & Groot, Holland) were grown on 15 L rockwool slabs and on 30 L bags of compost, in a heated plastic greenhouse, from December to June. A nutrient solution with the same chemical composition was used for the three substrates, varying the composition according to plant development. The irrigation period was pre-set and the irrigation frequency was controlled by solar radiation. Fruits were collected twice a week, from March to June, weighted and selected. There were no significant differences in yield and fruit quality between substrates. Commercial yield on GMC was 16.6 kg m^-2, on PBC 15.5 kg m^-2 and on RW 16.2 kg m^-2. Temperature in composts showed a higher resistance to daily variation. We observed a good root development after the crop, specially in GMC. Positive changes in the physical properties of composts occurred during the growing period, particularly the increase in water content of GMC and in aeration capacity of PBC, indicating a potential re-using the composts, which was lately confirmed by growing a second and third tomato crop, on GMC (open and closed systems¹) and on PBC (open system²).

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