Some aspects of nitrogen nutrition on selected Ilex

Three holly cultivars, Ilex crenata, Thunb. 'Helleri' and 'Rotundifolia' and Ilex cornuta Lindl. et Paxt. 'Burfordi' were grown in 3 liter containers at 200, 300, 400 and 500 ppm nitrogen (N). Significant correlation coefficients were found between plant growth (dry wt accumulation) and both leaf N content and soil solution nitrates, while low correlation coefficients were found between soil nitrates and plant growth. Shoot growth of 'Helleri' and 'Burfordi' was not increased by N levels higher than 300 ppm while 400 ppm N was optimal for 'Rotundifolia'.

The effects of 3N levels on tissue N fluctuations during a flush of growth on 'Helleri' were also studied. For all N levels, tissue N levels were shown to increase following the cessation of stem elongation until a level of tissue N was reached where a new flush of growth began. These N levels were approx the same for all N treatments. The time necessary to reach this level was dependent on the level of N added; 5 weeks for 300 ppm, 13 weeks for 150 ppm and 18 weeks for 50 ppm N. Once new growth began, tissue N levels began to decrease.

The response of 'Helleri' to 15 fertilizer treatments consisting of different time and lengths was studied. Fertilizer applied during a period following the cessation of stem elongation and before the next flush resulted in greater total N and shoot growth, regardless of whether it was also applied during other weeks or not. Root growth was suppressed by 3 or more fertilizer applications, regardless of the time of application.