SIMULATION OF TIMOTHY NUTRITIVE VALUE : A COMPARISON OF THREE PROCESS-BASED MODELS

Transcription

1 SIMULATION OF TIMOTHY NUTRITIVE VALUE : A COMPARISON OF THREE PROCESS-BASED MODELS Persson, T. 1, Höglind, M. 1, Van Oijen, M. 2, Korhonen P. 3, Palosuo, T. 3, Jégo, G. 4, Virkajärvi, P. 3, Bélanger, G. 4, Gustavsson, A.-M. 5 1 Norwegian Institute of Bioeconomy Research (NIBIO), Særheim, Norway 2 Centre for Ecology and Hydrology, UK 3 Natural Resources Institute Finland (Luke), Helsinki, Finland 4 Agriculture and Agri-Food Canada (AAFC), Québec, Canada 5 Swedish University of Agricultural Sciences (SLU), Umeå, Sweden

2 BACKGROUND Timothy is a widely grown forage grass in cold temperate regions. Physiological characteristics and nutritive value vary between cultivars. Climate, weather, soil conditions, and mangement practices affect yield and quality

3 BACKGROUND Process-based simulation models consist of equations, which represent the physiological processes behind sward growth and development and affect chemical composition. Different models respond differently to environmental and management factors, affecting the model prediction accuracy. Cultivar specific calibration improved the prediction of timothy yield with the models, CATIMO and STICS (Korhonen et al 2018, Field Crops Research 224: 37-47)

4 OBJECTIVES Compare the models BAGSRA, CATIMO and STICS as regards prediction accuracy of crude protein (CP) and fibre (NDF) concentration, and fibre digestibility (dndf) Determine how cultivar-specific calibration affects the prediction accuracy of these attributes

5 MODEL CHARACTERISTICS, CATIMO and STICS: All models calculate growth by radiation use efficiency (RUE). All models simulate leave and stem fractions. also simulates vegetative and generative tillers. All models calculate phenological development by growing degree days. In day length also affects development. All models simulate nitrogen responses. STICS simulates soil water and nitrogen in multi-layers, while and CATIMO simulate the soil in one single layer

6 MODEL CHARACTERISTICS In CATIMO and STICS, plant N requirements decrease with increasing shoot biomass. In, plant N requirements are determined by the sward LAI and the extinction coefficient. The amount of cell walls (NDF)/the digestibility of cell walls (dndf), increases/decreases with phenological stage in all three models. All models: Different rates of NDF change in stems and leaves CATIMO and STICS: NDF/dNDF also directly affected by temperature

7 Data on crude protein, NDF and dndf from field trials in four countries six varieties a wide range of climate and soil conditions, and N fertilizer regimes

8 SIMULATION SETTINGS Two types of calibration 1. Cultivar-specific calibration 2. Calibration of all cultivars together (generic calibration) Separate calibration and validation datasets. All simulations were initiated at the beginning of the growing season in the spring Calibrations techniques were allowed to differ between the models

9 CRUDE PROTEIN 0.3 CATIMO STICS Observed Crude Protein (g g DM -1 ) calibration validation CATIMO STICS Simulated Crude Protein (g g DM -1 )

10 NEUTRAL DETERGENT FIBRE 0.8 CATIMO STICS 0.7 Observed Neutral Detergent Fibres (g g -1 DM) validation calibration Champ Nuutti Grindstad Tammisto II Iki Jonatan Climax 1:1 line CATIMO STICS Simulated Neutral Detergent Fibres (g g -1 DM)

11 DIGESTIBILITY OF NDF 0.9 CATIMO STICS 0.8 Observed digestibility of Neutral Detergent Fibres (g g -1 NDF) calibration validation CATIMO STICS STICS val Simulated digestibility of Neutral Detergent Fibres (g g -1 NDF)

12 Number of Mean of Mean of Normalised rmbe d- observations observation simulation RMSE (%) (%) index Crude protein concentration (g g -1 DM) CATIMO STICS NDF concentration (g g -1 DM) CATIMO STICS Digestibility of NDF g g -1 NDF) CATIMO STICS

13 CONCLUSIONS NDF concentration and dndf predicted with similar accuracy as DM yield in previous studies Prediction of CP was poor compared with NDF and dndf Cultivar-specific calibrations improved the performance of CATIMO and STICS, but not of