Growth of tomato plants and changes in nutrient element concentrations in the rockwool system with a device to recycle used nutrient solutions

Abstract

The conventionally used open rockwool cultivation system has a problem of causing environmental pollution because the nutrient solution drained from the bed is discarded to the environment. We constructed a new rockwool system for tomato cultivation with a device to reuse the nutrient solution. With this revised system, freshly prepared nutrient solution is supplied to plants and its drainage is collected in the tank A. When this tank is filled to a preset capacity, the solution in this tank is supplied to plants and its drainage is collected in the tank B. When the tank A becomes empty but the tank B is not saturated, fresh nutrient solution is supplied to plants until the tank B is filled with used nutrient solution. Then, the nutrient solution in the tank B is supplied to plants and its drainage is collected in the tank C. When the solution in the tank C is saturated, nutrient solution in this tank is supplied to plants and its drainage is collected in the waste tank and discarded. This procedure is repeated until crop cultivation is halted. In this study, tomato (Lycopersicon esculentum Mill., cv. 'House Momotaro') was cultivated in the glasshouse for 6 months from September to March by using the revised semi-closed rockwool system and the conventional open rockwool system. Plant densities were 2000 plants/10a. The concentrations of nutrient elements in the rockwool slub differed with the systems, and Na concentrations were much higher in the revised system than in the conventional system. However, plant growth and fruit yields were not significantly different between the two systems. The revised semi-closed system showed a 87 to 99% reduction in the amount of nutrient elements discarded as compared with the conventional system. Possible problems in using the revised rockwool system are discussed.