Evaluation of Compost Leachate for Growing Nursery Trees on a Waste-Rehabilitated Field Site

Abstract

Compost run-off leachates are potential sources of irrigation water and nutrients. The objective of this study was to evaluate and compare growth response between nursery tree species irrigated with pond-collected compost leachate. Leachate was deficient in nitrogen (NO₃ -N < 0.02 mg L⁻¹) and phosphorus (0.40 mg P L⁻¹) and excess in potassium (316 mg K L⁻¹) also slight to moderate excess in sodium (138 mg Na L⁻¹. One- or two-year-old seedling whips of black locust (Robinia pseudoacacia L.), Carolina poplar (Populus x canadensis Moench), green ash (Fraxinus pennsylvanica March), hybrid poplar (Populus angulata x nigra L. var. plantierensis (Simon-Louis) Schneid.)] and silver maple (Acer saccharinum L.), and 2-year-old whips of hybrid poplar grown from hardwood cuttings, were planted in a field site rehabilitated with various organic wastes (wood chips, corrugated cardboard, and spent mushroom substrate-derived compost.) During each of two growing seasons (1998 and 1999), the leachates were applied 2-3 times weekly at two rates: Irrig I -fulfill crop water requirements with a 5% leaching fraction, i.e. about 12 L m⁻², and Irrig II with a leaching fraction of 20%, i.e. 17 L m⁻². There were also unirrigated (control) plots. All plots were fertilized with two levels of combined N and P fertilizer, 100 kg N+ 44 kg P ha⁻¹ (1 NP) and 200 kg N + 88 kg P ha⁻¹ (2 NP). Trunk diameter of all taxa and height of some taxa increased due to wastewater irrigation but there was no influence to application rates. With few exceptions, trunk diameter and tree height were larger with the higher NP application. Sodium accumulated consistently in leaves of all taxa due to irrigation treatments but the highest concentrations of 1.25 mg g⁻¹ were below recommended toxic values (<2.5 mg g⁻¹). Other foliar nutrients (N, P, K, Ca and Mg) showed inconsistent, little, or no accumulation, due to leachate irrigation and/or NP fertilizer. Throughout the study, there was no visual sign of nutrient toxicity or deficiency.