摘要 : To avoid the current water pollution from intensive glasshouse horticulture, closed systems have to be developed with recirculating drainage water. For crops with a high planting density, such as lettuce, shallow beds of coarse sa... 展开 To avoid the current water pollution from intensive glasshouse horticulture, closed systems have to be developed with recirculating drainage water. For crops with a high planting density, such as lettuce, shallow beds of coarse sand may be used if water and nutrient supply can be regulated adequately. The aim of the present study was to determine the rooting characteristics and root distribution of lettuce in sand beds, as affected by substrate depth, the distance to a drain, drip lines and drip points, and the excess of nutrient solution applied. The hypothesis was tested that a small excess and a large distance between drip points leads to local salt accumulations in the root environment and thus to a less homogeneous root distribution. 收起