Growth, photosynthesis and productivity of greenhouse tomato cultivated in open or closed rockwool systems

Two full spring season tomato crops (Lycopersicon esculentum Mill. 'Trust') were grown in an open rockwool system with standard rockwool feeding formulae (O-R; conventional method), and in closed rockwool systems with standard rockwool (C-R) or Nutrient Film Technique (C-NFT) feeding formulae (modified in 1997) in 1996 and 1997 to examine the feasibility of a fully closed rockwool production system with appropriate feeding formulae. The closed rockwool system with optimized feeding formulae achieved high marketable yield, similar to that of the open rockwool system. There were no differences in early plant growth, plant biomass or biomass partitioning, and in total fruit yield, size and grades except for the closed rockwool system with the standard rockwool feeding formulae (C-R), which had lower yield than C-NFT in the last month of harvest in 1996. The photosynthesis of old foliage was higher and the root systems at the end of the experiments were rated healthier in plants grown in the closed (C-R and C-NFT) systems than in plants grown in the open (O-R) system. Over 30% of water and fertilizer was saved with the closed systems in comparison to the conventional open system. These results demonstrated that closed rockwool systems with optimized nutrient feedings are economically and environmentally sound alternative methods for greenhouse tomato production in Ontario.