순환식 담액수경 상추재배에서 양액의 pH 변화는 미량원소 수준에 관계없이 생육 중기에 낮아지다가 생육후반에 회복되었는데 양액 내에 Humus첨가에 의해 양액의 pH 변화가 완만해졌다. 생육은 Humus첨가에 의해 양호한 경향을 나타냈고 미량원소수준이 높아질수록 저조하여 Cu · Zn농도 5ppm이상에서 황화현상 등의 피해가 발생하였으며, Humus 첨가에 의해 중금속에 의한 생체중 감소가 현저히 억제되었으며 과잉피해증상이 완화되는 경향을 나타내었다. 무기성분 흡수에서는 Zn은 흡수억제 효과가 없었으나 Cu원소의 흡수는 억제되어 중금속의 피해 우려시 Humus의 효과가 어느 정도 인정된다.

In the recirculating hydroponics, pH of nutrient solution was gradually decreased until the middle of growing-period, and then began to go up and reached the initial level at the latter of growing-period regardless of Cu·Zn content. Changes of pH was gently down for supply of humus in nutrient solution. The growth of lettuce was good with supply of humus, but it was decreased as Cu·Zn content was increased. Although leaf chlorosis was caused by excessive content of Cu·Zn as 5, 10 ppm, it was controlled by adding humus in nutrient solution, and fresh weight of lettuce was obviously improved by adding humus.

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