Effect of weed control with fibre mulches and herbicides on the initial development of spruce, birch and aspen seedlings on abandoned farmland.
Post-planting weed control methods on abandoned farmland were studied in three field trials in southern Finland using a completely randomized design with four treatments and 30 to 40 replications. Mulches of 60×60 cm (sheet mulch - strips of plane waste and plastic fibre, newspaper - waste paper slurry, wood chips, pure wood fibre slurry), herbicides (i.e. glyphosate or terbuthylazine alone or mixed and dichlobenil applied to 1 m2 spots), and hoeing treatments were compared to an untreated control plot. The study material consisted of two-year-old containerized aspen (Populus tremula), silver birch (Betula pendula) and Norway spruce (Picea abies) seedlings planted in spring 1996. The ground vegetation was dominated by Elymus repens, Deschampsia cespitosa, Cirsium arvense and Epilobium angustifolium. Monitoring of the trials over a 3-year period showed a moderate effect of weed control, which varied according to the method used and by the crop species. Significant growth responses were found with herbicide in spruce, wood chips in spruce and birch and with sheet mulch in aspen seedlings. Sheet mulch also encouraged vole nesting thus increasing damages. Generally, slurry mulches proved to be insufficiently durable. Mulching had a clear insulating effect, which may increase the risk of winter drought.