Combining Legume Groundcovers and Low Nitrogen Fertilization in a Short-rotation Fraser Fir (Abies fraseri) Cropping System: Effect on Productivity, Soil Fertility, and Nutrient Leaching

Abstract

High rates of inorganic fertilizers are used in conventional intensive production systems such as Abies fraseri (fraser fir) cropping systems for Christmas trees. Groundcovers can be used as green mulches, help reduce the use of farm chemicals, and provide several environmental benefits. We investigated the performance of a low-input cropping system by combining two legume cover crops [Dutch white clover (Trifolium repens) and alfalfa (Medicago sativa)] in combination with low rates of inorganic fertilizers as a step toward a more sustainable production system. The randomized block design comprised one cover crop and one of three applications of reduced rate inorganic fertilizer (75%, 50%, and 25% of the recommended rate). A conventional system using herbicides for weed control and the 100% rate of inorganic fertilizer was used as a control. Parameters measured included tree morphology, foliar nitrogen concentration, soil mineral nitrogen, and nitrate-N leaching below the root zone. A significant positive growth response (height and diameter) was obtained in all alfalfa-based cropping systems. This was accompanied by foliar nutrient concentrations similar to conventional plots and a reduction in nitrate-N leaching. However, in white clover-based cropping systems, the growth response was reduced (both height and diameter), suggesting competition for soil resources. In addition, the total nitrate-N leaching was higher in this system, suggesting an imbalance between mineral nitrogen availability and use in white clover-based cropping systems. We conclude that if the potential competition between cover crops and trees can be properly managed, legume cover crops can be effectively used to make intensive production tree-based systems more sustainable. Further studies related to mineralization and macronutrient flows are needed before any definite recommendation can be made about the use of these systems in large-scale production systems.