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Agronomic Modeling

Timothy Yield and Nutritive Value by the CATIMO Model

III. Validation for Eastern Canada

^a Norwegian Crop Res. Inst., Kvithamar Res. Cent., NO-7500 Stjordal, Norway
^b Soils and Crops Res. and Dev. Cent., Agric. and Agri-Food Canada, 2560 Hochelaga Boulevard, Sainte-Foy, QC, Canada G1V 2J3
^c Crop and Livestock Res. Cent., Agric. and Agri-Food Canada, Nappan, NS, Canada B0L 1C0
^d Soils and Crops Res. and Dev. Cent., Agric. and Agri-Food Canada, 1468 Saint-Cyrille St., Normandin, QC, Canada G8M 4K3
^e Atlantic Cool Climate Crop Res. Cent., Agric. and Agri-Food Canada, 308 Brookfield Road, St. John's, NF, Canada A1E 5Y7

^* Corresponding author (belangergf{at}agr.gc.ca)

Received for publication July 2, 2003. The Canadian Timothy Model (CATIMO) is a mechanistic simulation model of timothy (Phleum pratense L.) growth and nutritive value that features radiation interception and use efficiency, leaf and stem growth, leaf senescence, a N function based on the critical N concentration of whole plants, and cell wall (CW) concentration and digestibility of leaves and stems; the model was calibrated with measurements of timothy primary growth from one location (Fredericton, NB, Canada). In this paper, we compare the predictions of the CATIMO model with measurements from a total of six experiments conducted at four locations that cover the pedo-climatic conditions of eastern Canada (Lévis, QC; Nappan, NS; Normandin, QC; St. John's, NF). Across experiments, the root mean square errors (RMSE) for dry matter (DM) yield varied from 30.9 to 265.9 g DM m^–2 and averaged 123.9 g DM m^–2. Omitting one experiment in 1999, however, reduced the overall RMSE to 72.6 g DM m^–2, which is very close to the 65.9 g DM m^–2 reported for calibration. The RMSE values across experiments for N concentration (0.013 g g^–1 DM), in vitro true dry matter digestibility (0.052 g g^–1 DM), CW concentration (0.104 g g^–1 DM), and CW digestibility (0.064 g g^–1 CW) were higher than those obtained at the calibration site. At three of four locations, however, RMSE values were close to those of the calibration site. The CATIMO model seems robust enough to apply to situations different than those used for calibration, at least within eastern Canada.

Abbreviations: CW, cell wall • DM, dry matter • IVTD, in vitro true dry matter digestibility • LAI, leaf area index of green leaves • LWR, leaf to weight ratio • N_mmax, maximum nitrogen concentration • PAR, photosynthetically active radiation • RAW, readily plant available water • RMSE, root mean square error of estimation • RUE, radiation use efficiency • WAW, weakly plant available water