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.
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