Sward composition and grazer species effects on nutritive value and herbage accumulation

Abstract

In experimental grassland, plant species diversity has often been found to be related to productivity. However, it is not clear whether this relationship also exists in semi-natural permanent grassland, and how it is affected by the stocking system. We analyzed the effects of cattle (Bos taurus) and sheep (Ovis aries) grazing alone or in combination on annual herbage accumulation and nutritive value of a moderately species-rich sward (diverse sward) and its grass-dominated counterpart (grass sward) during 3 yr after the onset of a grazing experiment. The grass sward was established applying selective herbicides against dicot species before the start of the experiment, resulting in a reduction of plant species number by 35% and a yield contribution of dicots of <1%. Annual herbage accumulation was similar between sward types and was not related to plant diversity, functional group proportion, or grazing treatment. Complementary nutrient use might have been of similar importance in the grass and the diverse sward, due to a relatively high plant species number in the grass sward (9.2 species m -2). Additionally, the nutrient return via animal excreta likely prevented a nutrient limitation in both swards. Diverse swards produced herbage of higher nutritive value than grass-dominated swards, likely the effect of an increased percentage of highly digestible legumes and forbs. Grazing treatment had no effect on the nutritive value of herbage. However, postgrazing nutritive value was affected by the grazing treatment as a result of a larger selectivity by sheep. © 2012 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved.