Evaluating the change in orchardgrass (Dactylis glomerata L.) production associated with global warming in Northern Hokkaido, Japan: Effect of low water stress resulting from a decrease in soil water

The impact of global warming on changes in dry matter production (DMP) of an orchardgrass (Dactylis glomerata L.) located on three soils (coarse, medium and fine textured) in Northern Hokkaido, Japan, was estimated. The influence of low water stress resulting from a decrease in soil water on a change in impact was evaluated through simulations by using a climate change scenario and a previously validated grass growth model (Nakatsuji et al. 2002a). The effect of low water stress on growth during the first grass growing period (early May-early June) because of global warming would not be so intensive that the DMP would be expected to increase (1.2-1.4-fold of the present), except for fine-textured soil in low precipitation. In contrast, for the second grass growing period (mid June-early August), the effect of low water stress on growth would intensify over the years. An increase in DMP could be hardly expected in the case of low precipitation and finer-textured soil. The changes in DMP during the third grass growing period (mid August-mid September) with global warming and the influence of the amount of precipitation on these changes were negligible. The total DMP from the three cutting periods increased with global warming regardless of the soil texture and the amount of precipitation, although the finer the soil texture, the lower the total weight. However, the maximum ratio of the total DMP in the future to the present because of global warming was approximately 1.2-fold at most. This ratio was smaller than the previously reported value, estimated solely based on weather conditions over 100 years. It can be concluded that when we evaluate the change in grass production associated with global warming, it is important to take into account not only the effect of the increase in temperature and atmospheric CO2 concentration, but also the effect of the occurrence of low water stress resulting from a decrease in soil water, depending on the amount of precipitation or soil water retention characteristics.