Root activity of young Acacia mangium Willd trees: influence of stand density and pruning as studied by ³²P soil injection technique

• Published in: Agroforestry systems 2010, Vol.78 (1), p.27-38
• Main Authors: Kunhamu, T. K, Kumar, B. M, Viswanath, S, Sureshkumar, P
• Format: Article
• Language: English
• Subjects: Acacia mangium; Agriculture; Agronomy. Soil science and plant productions; Biological and medical sciences; Biomedical and Life Sciences; canopy; Cropping systems. Cultivation. Soil tillage; Density; forest trees; Forestry; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Injection; Life Sciences; measurement; nutrient uptake; phosphorus; plant density; Plant growth; Plant populations; Population density; pruning; radiolabeling; Roots; silvicultural practices; Soils; stand density; Stems; Subsoils; Tending. Growth control; Tillage. Tending. Growth control; Trees; Tropical environments
• ISSN: 0167-4366; 1572-9680
• DOI: 10.1007/s10457-009-9205-2

Initial spacing and pruning are silvicultural strategies that influence the resource acquisition capabilities of trees. A field study was conducted in the humid tropics of peninsular India to test the assumptions that: (1) high stand density of Acacia mangium induces greater root uptake capacity close to the stem and from the subsoil; and (2) crown pruning stimulates greater root uptake capacity at proximal points. Root activity pattern of two-year-old A. mangium was evaluated as a function of three population densities (1,250, 2,500 and 5,000 stems ha⁻¹), with, and without 50% crown pruning, using ³²P soil injection. The label was placed at 25, 50 and 75 cm lateral distances and at 30 and 60 cm depth. Low density stands (1,250 stems ha⁻¹) generally showed higher ³²P recovery (P < 0.01), which was exaggerated by pruning. Pruned low density stands had 34% root activity at 25 cm, as against 23% for unpruned. The low density stands also showed higher root activity at 75 cm, signifying greater root spread. We suggest that high stem densities favour restricted spread of absorbing roots and may facilitate competitive downward displacement of roots. Pruning the lateral shoots at low stem densities may simulate this to some extent. The net outcome of interactions, however, will depend on trade-offs between stem density and tree management over time.