SIMULATED GROWTH AND NITROGEN DYNAMICS OF A PERENNIAL RYE GRASS

The growth and nitrogen uptake of Italian Rye Grass (Lolium multifloru m Lam.) used as a catch crop were studied in 1988/1989 and 1990/1991 w ith the aim of determining the extent to which differences between the two years could be explained by variation in climatic conditions. The experimental field was situated about 50 km south of Halmstad close t o the Swedish west coast (56 degrees 30'N; 13 degrees 00'E, 10 m eleva tion). The SOILN model, which considers the major flows of nitrogen an d carbon in both plant and soil, was used to evaluate the importance o f three growth factors, i.e., solar radiation, temperature and nitroge n status, under autumn and winter conditions. The model was calibrated against measured total plant biomass (r(2) = 96%) and nitrogen (r(2) = 95%) together with soil mineral nitrogen in 1988/1989 and validated on an independent dataset in 1990/1991. Measured increases in biomass and nitrogen were much lower in 1990 than in 1988 (79% and 68% lower, respectively). The simulations were able to explain 90% of the observe d between-year variation in relative growth rate. The higher maintenan ce respiration in 1990 was the main factor responsible for the differe nces observed. In 1990, plant N was well simulated (r(2) = 89%), where as estimates of plant biomass was high (r(2) = 76%). (C) 1997 Elsevier Science B.V.