Testing the performance of ORYZA1, an explanatory model for rice growth simulation, for Mediterranean conditions

ORYZA1 is an explanatory model to simulate rice growth, development and lea f area index (LAI) under potential production. The present study aims at te sting the performance of ORYZA1 for Mediterranean conditions (farming pract ices, cultivars, weather) for fully irrigated direct-seeded rice. ORYZA1 wa s calibrated and validated with field data of two cultivars, a short-grain (Tebre) and a long-grain cultivar (L-202), grown in various years in the Eb ro Delta of Spain. Phenological development of the rice crop, daily dry mat ter production and leaf area development were calibrated. Tebre and L-202 h ad no significant differences in the total length of the development period . The pre-heading period, however, was longer and the post-heading period s horter in L-202 than in Tebre. This induced differences in translocation ch aracteristics, spikelet number per unit area, weight of the grains and harv est index. The following crop characteristics were similar between cultivar s: extinction coefficient (increased with development stage), dynamics of n itrogen distribution, partitioning of assimilates, relative death rate of l eaves, relative growth rate of leaf area during exponential growth, specifi c leaf area and a strongly decreasing specific stem green area. The simulat ed curve fitted much better the observations, which was clear from a strong ly reduced value of RMSE, when considering that LAI comprises the leaf blad e area only, without a photosynthetic contribution by stem green area. The model simulated rice growth very accurately until flowering. After flowerin g, however, divergences appeared and increased especially at the yellow rip e stage. From then on the crop did not grow much more, whereas it continued in the simulation. This reduction of growth rate was usually accompanied b y an increase in the relative death rate of leaves and the drying of the gr ains. The main source of error may be a limited understanding of the ripeni ng and sink limitation processes. A considerable yield gap between potentia l and observed yield remained. A climatic variability assessment over 10 ye ars; from 1987 to 1996, showed a small but correlated variation (r = 0.7) i n both simulated and measured rice yields. (C) 2000 Elsevier Science B.V. A ll rights reserved.