Effects of variation in shade level, shade duration and light quality on perennial pastures

Abstract

Two experiments examining the effect of artificial shade on pasture net herbage accumulation (NHA), botanical composition and soil characteristics were conducted between 1994 and 1999 at Whatawhata Research Centre. Both experiments included a range of shade levels (0–94%) and shade durations (3–12 months per year). Experiment 1 also included a light quality treatment, incorporating a range in the red:far red ratio (0.49–1.00). All three shading factors decreased annual NHA, with the most influential being the level of shade, which accounted for 68% of the variation and reduced NHA by 20–80% compared with open pasture. The second most influential factor was shade duration, which accounted for only 6% of the variation in NHA. Shading also led to changes in pasture botanical composition, most notably a decline in legume content in both experiments. There was no evidence that hairy pasture species (grasses or legumes) had any advantage over glabrous species under shade. At shade levels >60%, herbage nitrogen concentrations were elevated by 0.2 percentage points on a per unit dry weight basis, although reduced pasture NHA under higher shading meant lower demand for soil nitrogen. Potential nitrogen mineralisation measurements also indicated that nitrogen cycling is likely to be reduced under shading.