Agriculture Reference
In-Depth Information
photocatalytically treated with solar light and a system with untreated recycled
waste nutrient solution. The results showed, as measured by growth indices
such as stem length and stem thickness, that asparagus growth in the
photocatalytically treated system was superior to the untreated one.
Furthermore, the yield of asparagus spears was 1.6-fold greater in the
photocatalytically treated system, demonstrating the detoxification effect on
the phytotoxic compounds and also the killing effect on pathogenic
microorganisms. Miyama et al.(2009) [4] examined the effectiveness of
photocatalytic treatment under solar light irradiation of waste nutrient solution
emitted from a soilless cultivation system of tomatoes planted in rice hull
substrate from the viewpoint of conservation-oriented agriculture. The
phytotoxically active extract from rice hulls was treated with a TiO
2
-coated
porous alumina filter irradiated with ultraviolet light, and the phytotoxic
activities before and after irradiation were evaluated from the germination rate
of lettuce seeds.
The germination rate was recovered from 0% to 100 % after 4 days of
irradiation. The growth of tomatoes planted in rice hull substrate under actual
cultivation conditions was also observed in six repeated experiments over a 3-
year period by comparing tomatoes grown in a closed soil-less cultivation
system with photocatalytically treated waste nutrient solution under solar light
(photocatalytically treated system), with tomatoes grown in a closed system
with untreated waste nutrient solution (untreated system).
All results showed us that tomato growth in the photocatalytically treated
system was significantly higher than that in the untreated system in six
experiments over 3 years, and yields in the photocatalytically treated system
were comparable to those in a currently used open cultivation system using
rockwool substrate [6]. These results suggest that incorporating photocatalytic
treatment of waste nutrient solution under solar light irradiation will allow
conservation oriented closed soilless cultivation systems to be realized.
Zero release of waste nutrient solution is necessary for sustainable
agriculture, which is more important for hydroponic systems in protected
systems, e.g. greenhouse and plant factory. Realization of zero release of
hydroponic systems means to balance nutrient elements, to remove pathogens
and harmful substances, the pre-requirements for complete utilization of
nutrients and healthy durative running.
