OSYAQ, an organ-specific growth model for forage grasses.

The effects of different stem-to-leaf proportions on the yield and quality of forage grasses is a question of importance to plant breeders. This paper describes the growth submodule of OSYAQ, an organ-specific yield and quality model. The model input includes daily average air temperature, precipitation, potential evapotranspiration and incoming global radiation. The major processes implemented in the growth submodule are photosynthesis, maintenance and growth respiration, recycling of senescent plant material and remobilization of reserves. The model calculates separately yield formation for stem, leaf and ear. Available assimilates are partitioned to the various plant parts according to the concept of relative sink strength. Calibration and validation were based on a 2-year and a 1-year field trial, respectively, carried out under long- and short-day conditions with Lolium multiflorum ssp. gaudini. These tests indicated a good performance of the model for the long-day growth but showed some deficiencies for regrowth after defoliation under conditions of extreme water shortage. The paper discusses these results and possible improvements. It concludes that the growth module of OSYAQ provides a suitable tool for the analysis of the effects of varied stem-to-leaf ratios on yield. [ABSTRACT FROM AUTHOR]