Projecting Yield and Nutritive Value of an Alfalfa-Timothy Mixture Under Climate Change.

Modelling studies of the effect of climate change on forage crops have focused on individual species even though legume-grass mixtures are most common on dairy farms. Our objective was to assess the potential impact of future climate change on yield and nutritive value of alfalfa (Medicago sativa L.) and timothy (Phleum pratense L.) grown in a mixture, with or without the implementation of an adaptation strategy (a modified schedule of harvest including additional cuts). The Integrated Farm System Model (IFSM) was used to simulate the growth of an alfalfa-timothy mixture for two contrasting climate areas in eastern Canada [Quebec Southwest, QSW, 2000 growing degree days (GDD; 5°C basis); Quebec East, QE, 1400 GDD] and for three periods (reference period, 1971-2000; near future, 2020-2049; and distant future, 2050-2079). Forage growth is expected to start up to 26 days earlier in the distant future than under the reference period. Without any adaptation strategy, annual dry matter (DM) yield in the distant future will increase (+1.2 Mg ha^-1) at the colder area (QE), but decrease (-0.13 Mg ha^-1) at the warmer area (QSW). At both areas, forage first cut yield is generally expected to be favored by climate change while second and third cuts are expected to suffer losses because of higher water and temperature stresses. Nutritive value of the forage mixture is expected to decrease under all future scenarios because of higher GDD accumulation between cuts. With the adaptation strategy, forage mixture DM yield is expected to increase in both areas (+2.0 Mg ha^-1 at QE and + 1.3 Mg ha^-1 at QSW) and no significant change of the nutritive value is expected. The increased proportion of alfalfa in the mixture should offset the decrease of nutritive value due to yield increase.