セル培地に必要な散水量と植物体の大きさの関係

In order to clarify the problems with overhead irrigation systems for cell transplant production, uniformity of water supply by a boom spraying system was investigated. Furthermore, uneven water soaking into individual cell medium caused by plant cover growing in such cells was investigated. The amount of water supply from a boom spraying system varied considerable with the arrangement of the nozzles. Although a larger number of nozzles was set on the boom, the maximum amount of supplied water in the central part of the boom was about twice as much as that at each end of the boom. When no plant was grown in the cells, uniform water supply to individual cell mudium was obtained by a downright sprinkler system. However, when stock (Matthiola incana R. Br.) plants were grown in cells, variation in the amount of water soaking into the medium increased noticeably with increase in the plant size growing in the cells and with a decrease in the amount of supplied water. Plant covers with overlapped leaves may disturb the uniformity in the amount of water soaked into individual cell medium. As twice the water consumption may be required for uniform water supply into individual cell medium with an overhead irrigation system, a subirrigation system may be desirable for economical and ecological automatic irrigation to produce cell transplants on a large scale.

セル育苗における灌水方法として用いられている頭上散水法の問題点を明らかにするため，実際の苗生産施設において，ブーム式の頭上散水装置による育苗ベンチ内の散水むらを調べた．また，苗齢（23，42日齢区）の異なるストックセル苗に散水ノズルによって散水（１/２セルトレイあたり０，150，300，450）した場合のセルごとの水分吸収量の変動を調べた．ブーム式の頭上散水装置による散水量は，ノズルからの散水の重なり程度によって大きく異なり，散水量の最大値は最小値の約２倍であった．ブームの中央部においても散水量にばらつきがみられ，最大30%程度異なった．均一な散水を行った場合であっても，セルで植物が生育している場合には，散水量が少ないほどセルあたりの灌水量の変動が大きくなった．また，植物体（葉面積）が大きいほど，変動が大きくなった．以上のことから，頭上散水法ですべてのセルに必要量散水するには，蒸発散量の２倍以上の散水が必要と推定され，セル育苗の灌水自動化にあたっては，灌水の均一化，養水分の利用効率の面から，頭上散水法より底面給水法を採用することが望ましいと考えられた．