LINGRA, a sink/source model to simulate grassland productivity in Europe

A simulation model for the prediction of the productivity of Lolium perenne L. grasslands is described and validated. Simulated key processes are ligh t utilization, leaf formation, leaf elongation, tillering, and carbon parti tioning (storage, shoot, root). Source- and sink-limited growth are simulat ed independently. Sink-limited growth is characterized by temperature-depen dent leaf expansion and tiller development, whereas source-limited growth i s determined by photosynthetic light-use-efficiency of the canopy and the r emobilization of stored carbohydrates in the stubble. At each integration s tep, commonly 1 day, the available amount of carbon from the source is comp ared with the carbon required by the sink. The actual growth is determined by the minimum value of either the sink or the source. If the source is in excess of the sink, the surplus is allocated to storage carbohydrates in th e stubble. This storage carbon is available for remobilization at times tha t the sink requires more carbohydrates than are available from photosynthes is. In contrast to previous grassland models, LINGRA describes regrowth aft er defoliation in a mechanistic way, balanced by temperature-driven remobil ization of stored carbohydrates. In order to validate LINGRA, an extensive set of experimental data was used, derived from measurements at 35 sites in Europe. The average error between the observed and predicted yields was 14 % at the level of irrigated, and 19% at the level of non-irrigated, treatme nts for the whole of Europe. (C) 1998 Elsevier Science B.V. All rights rese rved.