Abstract
Although coconut coir has been drawing a lot of attention as an alternative medium instead of rockwool in hydroponics, the adequate use of coconut coir has not been established due to the lack of information on its hydraulic properties. To reveal the properties and their differences among coconut coir and other growing media, we measured water retention curves and hydraulic conductivities of sand, rockwool, and coconut coir in a wide range of moisture conditions. The coconut coir, consisting of many smaller pores, could securely hold more moisture than other media, but did not permit active water flow due to its minimal hydraulic conductivity. Based on these measurements, we determined physical parameters characterizing each hydraulic property and simulated moisture conditions in the media under testing for a subirrigation system accompanying steady surface-evaporation of 1.0 cm d-1and a continuous water supply from ground water at a shallow depth. For the sand and the rockwool, suction of water less than15cm was simulated near their surfaces and thus the profile of volumetric water content (θ) locally decreased in the zone. Although a similar θ-profile was simulated for the coconut coir as well, the suction at the surface showed more than 160 cm. Judging from these results, we concluded that the moisture condition of horticultural media tested here was sensitive to boundary conditions such as evaporation, irrigation, and drainage as well as their hydraulic properties.
