Effect of planting density on dry matter partitioning in young ‘Laetitia’ / ‘Marianna’ plum trees grown in lysimeter tanks

Abstract

The effects of increasing planting density on young lysimeter tank-grown plum trees were investigated. Seasonal increases in stem circumference, and average shoot lengths, decreased significantly (P = 0.05) as the number of trees per 1.4 × 3.0 m tank increased from one to three. Total single-tree dry masses after three seasons were smaller, by 17.8% in the 2-tree tank⁻¹ and 53.2% in the 3-tree tank⁻¹, than in the 1-tree tank⁻¹ treatment. Corresponding decreases in fruiting spur dry mass (DM) tree⁻¹ were 46.3% and 64.8%. Ratios of topgrowth (above graft union) DM tree⁻¹ to rooting system (below graft union) DM tree⁻¹ increased from 1.98 to 2.62 to 3.04 in the 1-, 2- and 3-tree tank⁻¹ treatments, respectively. Branch DM made up 26.5%, and stem DM 68.9%, of the single-tree topgrowth DM in the 1-tree tank⁻¹ treatment but, in the 2- and 3-tree tank⁻¹ treatments, branch DM increased to approximately 60.3%, and stem DM decreased to approximately 35.9% of the top- growth DM. Leaf, fruit, shoot and < 3 mm diameter root nitrogen contents increased with planting density. By extrapolation, total tree DM ha⁻¹, and fruiting spur DM ha⁻¹, are greater at 4762 than at 2381 or 7143 trees ha⁻¹.