Climate change impacts of legume-grass swards: implications for organic farming in the Federal State of Brandenburg, Germany

Multispecies legume-grass swards (LGS) within crop rotations are the primary source for nitrogen and livestock forage in organic farming systems (OFS) in Europe. At the same time, LGS are very susceptible to the effects of climate change on OFS in dryer regions. In order to predict changes in annual and seasonal LGS yields, the number and dates of LGS cuts and drought impact, an empirical statistical yield model based on alfalfa (A) and red clover (B) was applied to two of the driest areas within Germany: the 'Spreewald' (SP), with sandy soils only suited for red clover and the 'Uckermark' (UM) with sandy loams. Weather data series from 1972 to 2008 and two regional warming scenarios for 2062-2092, namely 'Dry' and 'Wet', were used to calculate the impacts. Only the scenario 'Dry' predicts an annual yield reduction (about 20 %), for both regions. This impact can be attributed to (1) the first cut is early by four weeks (decreasing the yield by 0.5 t ha(-1)), (2), the third cut is often delayed (caused by water deficiency) and (3) eventual impracticality of a fourth cut. In contrast, the second cut increased by 1 t ha(-1) for 'Wet'. In SP, frequent severe drought impacts are predicted for red clover LGS. This deleterious impact of the 'Dry' scenario can be partially compensated only in UM when alfalfa is used, which showed lower susceptibility to drought. Along with the predicted yield reduction, an increased vulnerability of organic farms in both study regions cannot be prevented.