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MODELING

Timothy Yield and Nutritive Value by the CATIMO Model

I. Growth and Nitrogen

^a Norwegian Crop Res. Inst., Kvithamar Res. Cent., NO-7500 Stjordal, Norway
^b Soils and Crops Res. and Dev. Cent., Agric. and Agri-Food Can., 2560 Hochelaga Blvd., Sainte-Foy, QC, Canada G1V 2J3

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

Received for publication December 4, 2000. Mechanistic simulation models can assist in developing recommendations to optimize yield and nutritive value and in understanding the complex interaction among plant growth, nutritive value, and environmental conditions. In this paper, we present the growth and N concentration modules of an integrated model [CATIMO (Canadian Timothy Model)] of timothy (Phleum pratense L.) primary growth and nutritive value. This growth model features radiation interception and use efficiency, leaf and stem growth, leaf senescence, and a N function based on the critical N concentration of whole plants. Model parameters were calibrated to key model attributes: leaf area index (LAI); forage N concentration; and leaf, stem, and forage dry matter (DM) yields. Calibration measurements were taken weekly on timothy primary growth in four different years at one location (Fredericton, NB, Canada). Overall, the model satisfactorily fitted the measured values with root mean square errors of 32.8, 42.0, and 65.9 g m^-2 leaf, stem, and forage DM yield, respectively. The model tended to underestimate stem DM yield at the end of the primary growth cycle, overestimate forage N concentration under nonlimiting N conditions, and underestimate N concentration under limiting N conditions. The model satisfactorily fitted LAI in 3 of 4 yr. Summary statistics of the calibration indicate a successful description of growth and development of the essential plant components required for modeling digestibility.

Abbreviations: DM, dry matter • LAI, leaf area index • PAR, photosynthetically active radiation • RGRL, relative growth rate of leaf area • RMSE, root mean square error of estimation • RUE, radiation use efficiency • SLA_n, specific leaf area of new leaves • TSUM, temperature sum

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