Dactylis glomerata growing along a light gradient in the central Appalachian region of the eastern USA III. Nonstructural carbohydrates and nutritive value

Microsite conditions influence plant development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in woodlots. A field experiment was conducted to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zone (E^sub O^, E^sub W^) microsites influenced the quantity and distribution of nonstructural carbohydrate (TNC) and crude protein (CP) among plant parts of defoliated orchardgrass. Plants established in spring (SP) or late summer (LS) were clipped each time mean sward height reached 20 cm. Microsite conditions influenced nutritive value of herbage. Nutritive value was acceptable when not more than 45-50% light attenuation (as a function of shading by nearby trees) occurred relative to open pasture. Twice as much TNC accumulated in stembases of LS compared to SP plants. Concentrations of TNC were least in plants growing at W, regardless of planting time. Stembase TNC depletion occurred in SP plants, regardless of microsite, and LS plants growing at W. CP concentrations were greater in herbage from W compared to O sites, suggesting the N needs of the plant were met with minimal fertilizer N inputs. The ratio of C:N and thus herbage energy expressed as total digestible nutrients (TDN), relative to CP declined as shade increased. Increased protein content is offset by lower fiber, lower nonstructural carbohydrate and the possibility of reduced preference by grazers. Nutritive value is improved by modest amounts of shade relative to plants growing in full sunlight, and allowing cool temperate origin grasses to vernalize is beneficial in terms of productivity, nutritive value, and persistence.[PUBLICATION ABSTRACT]