الفهرس 
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Abstract
This work was executed during two successive seasons of 2019 and 2020 in the nursery and Laboratory of Faculty of Agriculture, Minia University. The aim of this study was to investigate the response of vegetative and root growth characters and some chemical composition of Delonix regia seedlings to four percentages of humic acid (0, 1, 2 and 4%) and four fertilization treatments (control, 100% NPK, Minia Azotein and 75% NPK + Minia Azotein), as well as, the interaction between them.
The obtained results could be summarized as follows:
I-Effect of humic acid on:
I-A- Vegetative and root growth parameters:
All studied parameters of Delonoix regia seedlings, namely plant height, stem diameter, number of branches and leaves/plant, leaves fresh and dry weights/plant, stem + branches fresh and dry weights, aerial plant parts fresh and dry weights/plant, number of roots/plant and fresh and dry weighs of roots/plant significantly increased by adding Delonix regia with humic acid at 1, 2 and 4% compared with control. The high percentages of humic acid (4%) was the most effective treatment.
I-B- Chemical composition:
Supplying humic acid at three used percentages led to significantly increased in the contents of chlorophyll a, b and carotenoids, as well as, uptake of N, P and K % over the control.
The highest values were obtained with the high percentage of humic acid (4%).
II- Effect of bio. and/or mineral NPK fertilization treatments on:
II-A- Vegetative and root growth parameters:
All plant growth parameters were significantly increased due to all used treatments of bio. and/or mineral NPK fertilization compared with control treatment.
The treatments of 100% NPK followed by 75%NPK + Minia Azotein in all cases gave the significantly highest values without significant differences between such two superior treatments.
II-B- Chemical composition:
Supplying humic acid at three used percentages led to significantly increased in the contents of chlorophyll a, b and carotenoids, as well as, uptake of N, P and K% over the control. The highest values were obtained with the high percentage of humic acid (4%).
The two treatments of 100% NPK, 75% NPK + Minia Azotein led to significant increase in contents of chlorophyll a, b and carotenoids, as well as, enhanced the percentages of N, P and K as compared with control.
The highest values were obtained by used 100 % NPK or 75% NPK + Minia Azotein.
III-Effect of the interaction treatments on:
III-A- Vegetative and root growth parameters:
The interaction between main and sub plot (A×B) treatments was significant for all test parameters.
The best interaction treatments for all test parameters were 4% humic acid in combination with mineral NPK (full dose, 100%) or 75% NPK + Minia Azotein.
III-B- Chemical composition:
The interaction between main and sub plots (A×B) were significant for test parameters, except in case of P%. The same treatments of 4% humic acid plus 75% NPK + Minia Azotein recorded the highest values in this concern.
RECOMMENDATION
from our results, it could be recommended to supply Delonix regia with humic acid 4% in combination with 100% NPK or 4% humic acid with 75% NPK + Minia Azotein biofertilizer to accelerate the growth of plants.