2021 journal article
Productivity and Profitability of Poplars on Fertile and Marginal Sandy Soils under Different Density and Fertilization Treatments
Forests.
We evaluated the productivity and profitability of four highly productive poplars including Populus deltoides Γ P. deltoides (DD β140β and β356β), P. deltoides Γ P. maximowiczii (DM β230β), and P. trichocarpa Γ P. deltoides (TD β185β) under two densities (2500 and 5000 trees haβ1), and three fertilization treatments (0, 113, 225 kg nitrogen haβ1) at three sandy coastal sites varying in soil quality. Green stem biomass (GSB) was estimated from the sixth-year stem diameter. Leaf-rust (Melampsora castagne) and beetle damage (by Chrysomela scripta Fabricius), the leaf area index (LAI) and foliar nitrogen, were measured in year two. At all sites, DD and DM had higher survival (>93%) than TD (62β83%). DD produced greater GSB (92.5β219.1 Mg haβ1) than DM (54β60.2 Mg haβ1) and TD (16.5β48.9 Mg haβ1), and this was greater under the higher density (85.9β148.6 Mg haβ1 vs. 55.9β124.9 Mg haβ1). Fertilization significantly increased GSB on fertile soil but not marginal soils; a higher rate did not significantly enhance GSB. Leaf rust was higher for fertile soil (82%) than marginal soils (20β22%), and TD β185β (51% vs. others 34%). C. scripta damage was higher for the higher density (+42%) than lower density, and TD β185β (50% vs. others >38%). LAI was higher on fertile soil (1.85 m2 mβ2) than marginal soils (1.35β1.64 m2 mβ2), and under the lower density (1.67 m2 mβ2 vs. 1.56 m2 mβ2). The high GSB producer DD β356β had the lowest LAI (1.39 m2 mβ2 vs. 1.80 m2 mβ2). Foliar nitrogen varied among genomic groups (DD β140β 1.95%; TD β185β 1.80%). Our plots were unprofitable at a 27 USD Mgβ1 delivered price; the biggest profitability barriers were the high costs of higher density establishment and weed control. The best-case treatment combinations of DD (β140β, β356β) would be cost-effective if the price increased by 50% (USD 37.54 Mgβ1) or rotations were 12 years (fertile-soil) and longer (marginal soils). The requirement for cost-effectiveness of poplars includes stringent and site-specific weed control which are more important than fertilizer applications.