Utilization of Snow and Geothermal Cold Heat for Temperature Control and Head Production in Witloof Chicory Hydroponic Forcing Culture in Summer

The exhaustion of finite fossil fuels and the impact of their mass use on the environment are of global concern. Attention is focused on the use of renewable energies such as sun, wind power and geothermal heat. The use of these energies is also desired in greenhouse horticulture, where large amounts of electric power and fossil fuels are employed (Kawamura et al., 2006; Fukui et al., 2009). Examples of using renewable energy in agricultural production are heating the inside of greenhouses through biomass combustion (Kawamura et al., 2006) and crop preservation using snow (Nakamura and Osada, 2001; Ishihara et al., 2005; Nikaido et al., 2014). However, using natural energy in agricultural production can be difficult as its abundance and form depending on geography and season. Previous research suggests that its unstable nature and energy smallness can be compensated by combining multiple energy types and inputting it locally (Angelis-Dimakis et al., 2011). In recent years, the demand for Western vegetables, including witloof chicory (Cichorium intybus L.), has increased in Japan (Ohtani, 2004), where almost all witloof chicory to date has been imported. However, doing so is expensive, and as such, domestic production of witloof chicory is anticipated for introduction to the Japanese market at a low price and high quality. Cultivation of witloof chicory comprises two stages: firstly, plant growing and harvesting of chicory roots in an open field and, secondly, implementing forcing culture of harvested roots for production of etiolated heads. Chicory roots are generally stored at a low temperature of roughly 0 °C and high relative humidity until forcing culture is implemented. The storage period is cultivar-dependent (König and Combrink, 2002). Forcing culture is generally carried out by employing high-density planting in a dark space under a controlled and constant temperature of 14 to 18 °C (Morishita, 1988). High temperatures cause rapid growth of loose and elongated heads, whereas low temperatures reduce growth rate and produce shorter and tighter heads (Ryder, 1998). Since loose, irregular shaped or small heads are not marketable (Sterrett and Savage, 1989), temperature control within a suitable range is important in forcing culture. In order to produce etiolated heads throughout the year, special equipment is needed for controlling the temperature within a suitable range in Japan (14 to 18 °C), particularly in summer and winter. In the commercial production of chicory heads, electrical air conditioning systems are applied in the forcing room, but this is a costly process. Since forcing culture can be carried out in an enclosed and narrow space, it is potentially viable to control temperature using natural heat sources, despite the limited energy density, compared to fossil fuels. Several studies have explored the feasibility of geo-