Abstract
In a previous study, the crop simulator CropSyst was evaluated against crop data collected on rice varieties grown in Northern Italy. The need of model re-parameterization became apparent after investigating new field data, as inconsistencies in the simulation of leaf area index emerged for Indica-type varieties. Key parameters (specific leaf area, stem-leaf partition, extinction coefficient, light-to-biomass conversion efficiency) derived from field measurements (respectively, 27 square m/kg, 3.6 square m/kg, 0.53, 3.2 g/MJ) considerably differed from those previously obtained via calibration (39 square m/kg, 1.5 square m/kg, 0.50, 3.0 g/MJ). Such new parameters are informative for suitable modelling of rice systems. The agreement between simulated and observed above ground biomasses was similar with both parameter sets: average general standard deviation = 25% (previous) and 26% (new); average modelling efficiency = 0.90 (previous) and 0.87 (new). Such comparisons demonstrate as the accumulation of aerial biomass in crop models can be depicted in different ways and reasonable estimations can be achieved by different pathways (not all acceptable). A check on parameters like the one performed here (field measurements versus calibrated parameters) is worth to give protection against spurious conclusions while indicating whether the parameterization is conceptually consistent and related to reality.
Highlights
Process-based simulation models for estimating crop growth and development were built and revised over the past decades
The need of model re-parameterization became apparent after investigating new field data, as inconsistencies in the simulation of leaf area index emerged for Indica-type varieties
Our estimation of LtBC (3.20 g above ground biomass (AGB) MJ-1 intercepted photosynthetically active radiation (PAR)) is higher than those commonly found in the literature (e.g. 2.39 g MJ-1, Kiniry et al, 1989) probably because our procedure led to obtain a potential value which is not affected by sub-optimal thermal conditions
Summary
Process-based simulation models for estimating crop growth and development were built and revised over the past decades (e.g. volume 18 of the European Journal of Agronomy: issues 1-2, 2002; issues 3-4, 2003). Process-based crop models give estimates of yield and harvest time based upon soil characteristics and weather dynamics, under different management scenarios. For this reason, modelling approaches have been used in a wide variety of applications at field, farm and regional scale (see, for instance, proceedings from Farming Systems Design 2007 - International symposium on Methodologies for Integrated Analysis of Farm Production Systems, Catania, Italy, http://www.iemss.org/farmsys). Quantitative information regarding biomass accumulation and leaf area evolution remains limited or inconclusive
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