Effects of Nitrogen Supply and Removal of Outer Leaves on the Head Development of Cabbage Plants

Abstract

Cabbage (Brassica oleracea L., capitata group) plants were grown in nutrient solutions containing NO₃-N at 5, 50, and 500ppm. At the beginning of head formation, the outer leaves were removed in various ways, and the effects of the nitrogen supply and the defoliation on the head development were studied.
The head weight increased greatly with an increase of the nitrogen supply from 5 to 50ppm N and decreased slightly at 500ppm N. At 50 or 500ppm N, the head weight decreased slightly following the removal of the middle and lower outer leaves (i.e. the upper outer leaves were kept intact), while greatly following the removal of the upper and middle outer leaves. At 5ppm N, the head weight was so small that no clear effect of the defoliation was recognized. The total N, 80% ethanolsoluble N, and NO₃-N contents in the plants increased with an increase of the nitrogen supply and with the removal of the upper and middle outer leaves. The total sugar content was lower at 5 and 500ppm N than at 50ppm N, and decreased with the removal of the upper and middle outer leaves. The ratio of the total carbohydrate to the total N contents of the outer leaves was about 10 in the intact (control) plants which were grown at 50ppm N and had the largest head weight.