A watering/drainage arrangement for a multi-layer horticultural structure wherein during watering, water from a series of water release outlets is sprayed through an aperture of a flood tray which fills to a selected level and maintained at this level by the continued supply of sprayed water through the water release outlets and the drainage of overflow via a weir edge of the flood tray and during drainage, supply of water to the release outlets is terminated thereby preventing water being sprayed into the aperture of the flood tray thereby allowing the discharge of water through the aperture of the flood tray.多層植物栽培構造体用灌排水装置であって、該装置は、灌水中、一連の放水口からの水を、冠水トレイの開口部を通して噴霧し、それにより選択水位まで充填し、その水位で、放水口を通して連続して噴霧水を供給し、且つ冠水トレイの堰縁部を経て溢出分を排水することによって維持し、排水中に、放水口への給水を終了することで、冠水トレイの開口部中に水を噴霧させず、それにより冠水トレイの開口部を通して水を流出可能にする。【選択図】図２
