Growth of Dactylis glomerata along a light gradient in the central Appalachian region of the eastern USA: I. Dry matter production and partitioning

Abstract

Microsite influences on resource allocation related to silvopastoral swards undergoing repeated defoliation are unclear. Defoliating traditional pasture species according to canopy development criteria may not be appropriate when the plants grow as understory crops in woodlots. An experiment using container-grown plants was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zones (E O, E W), representing the partial shade conditions found in silvopastoral settings, influenced productivity and dry matter allocation in Dactylis glomerata L. Plants established in spring (SP) and late summer (LS) were clipped each time mean sward height reached 20 cm. Dry matter production differed for SP and LS plantings, and was greater in O than W sites. Dry matter allocation to shoots of SP plants indicated some agronomic benefit associated with the E O and E W sites. Leaf mass did not vary with irradiance, but stembase mass did. The SP plants had numerous small tillers whereas LS plants were composed of comparatively fewer but more massive tillers. Plants growing at O, E O and E W were similar, whereas plants in the W site were smaller and had the fewest tillers regardless of planting time. Results suggest that defoliation management for shaded components of silvopastoral systems should be based on some index other than sward height, and that management criteria might change during the growing season. Less intensive removal (e.g., 10-cm rather that 5-cm residue) should be considered for defoliated, shade grown plants, since this could allow more stembase and nonstructural carbohydrate storage tissues to remain.