تأثير إضافة حامض الهيوميك والرش بمنظم النموCPPU في نمو ثالثة أصول من الحمضيات

Effect of Humic Acid Application and CPPU Growth Regulator Foliar Spray on the Growth of Three Citrus Rootstocks

Abstract
This study was conducted in the shade of the Department of Horticulture and Landscape, College of Agriculture, University of Kerbala, during the period from 1/ 3/ 2024 to 1/ 11/ 2024. The aim was to investigate the effects of soil addition of humic acid and spraying with the growth regulator CPPU on certain vegetative, root, and chemical traits of citrus seedlings. The experiment was carried out as a factorial trial within a Randomized Complete Block Design (RCBD) with three factors and three replications. The first factor involved the application of humic acid at three concentrations (0, 3, and 6 g L-1). The second factor consisted of foliar application of the growth regulator CPPU at three concentrations (0, 5, and 10 mg L-1). The third factor included three citrus rootstocks (Rangpur, Sour Orange and Macrophylla).
The results can be summarized as follows:
1. The results revealed significant differences among the concentrations of humic acid, where the concentration of 6 g L-1 outperformed the others by recording the highest means for several traits. These included seedling height (37.04 cm), stem diameter (5.075 mm), number of leaves (197.74 leaves seedling-1), number of branches (4.330 branches seedling-1), leaf area (422.86 cm²), dry weight of the shoot system (13.110 g), dry weight of the root system (5.755 g), root length (50.72 cm), root volume (29.425 cm³), total chlorophyll content in leaves (86.323 mg 100 g⁻¹ fresh weight), carbohydrate percentage (15.934%), total protein content (11.099%), as well as leaf concentrations of nitrogen (1.775%), phosphorus (0.470%), and potassium (1.785%), compared with the control treatment.
2. The results also demonstrated that the concentrations of CPPU foliar application had a significant effect on the studied traits. The concentration of 10 mg L-1 recorded the highest means for seedling height (32.40 cm), stem diameter (5.036 mm), number of leaves (197.07 leaves seedling-1), number of branches (4.354 branches seedling-1), leaf area (397.15 cm²), dry weight of the shoot system (12.633 g), dry weight of the root system (5.637 g), root length (45.72 cm), root volume (29.069 cm³), total chlorophyll content in leaves (75.923 mg 100 g-1 fresh weight), carbohydrate percentage (15.322%), total protein content (12.166%), as well as leaf concentrations of nitrogen (1.946%), phosphorus (0.442%), and potassium (1.570%). This treatment significantly outperformed the other concentrations.
3. The results indicated that citrus rootstocks differed significantly in the studied traits. Sour orange rootstock outperformed the others in seedling height (33.31 cm), leaf total chlorophyll content (74.630 mg 100 g-1 fresh weight), carbohydrate percentage (14.693%), total protein content (10.856%), and leaf nitrogen concentration (1.737%). In contrast, Rangpur rootstock exhibited superiority in stem diameter (4.963 mm), number of branches (4.123 branches seedling-1), number of leaves (223.96 leaves seedling-1), leaf area (428.02 cm²), dry weight of the shoot system (13.700 g), dry weight of the root system (5.807 g), root length (51.69 cm), root volume (28.455 cm³), as well as leaf phosphorus (0.425%) and potassium (1.498%) concentrations. Meanwhile, Macrophylla rootstock recorded the lowest means for the aforementioned traits.
4. The interaction treatments, both two-way and three-way, showed significant differences in the studied traits. Notably, the triple interaction treatment (Rangpur rootstock + 6 g L-1 humic acid + 10 mg L-1 CPPU) resulted in a significant increase in most vegetative and root traits, as well as in leaf phosphorus and potassium concentrations, compared with the other treatmen