Seasonal variation in productivity in semi-natural grasslands

Abstract

The growth potential of four semi-natural grasslands with rotational grazing was studied during four growing seasons. A crop growth model was used to quantify growth potential and to separate the influence of weather variables from factors related to the plant stand. The investigation revealed a high variability in dry matter (DM) production among years during the study period due to weather. There was also found to be a clear seasonal variation. The general shape of the DM production curve, with a rapid spring growth (the maximum relative growth rate (R s )=0.16 g g−1 day−1), a midsummer depression (R s =0.06 g g−1 day−1), and a second peak of growth in late summer (R s =0.09 g g−1 day−1), was the same for all years and for all fields. The model underestimated production when cover of herbs was low in spring and overestimated production when cover of herbs was high in spring. The seasonal and among years variation in DM production entailed a parallel large variability in the numbers of grazing animals (from 11 to 43 heifers ha−1) the area could sustain.