Timothy Yield and Nutritive Value by the CATIMO Model

Abstract

Growth and nutritive value of forage crops have rarely been integrated into one mechanistic computer simulation model. In a companion paper, we described the growth and N concentration modules of an integrated model of timothy (Phleum pratense L.) primary growth and nutritive value, known as CATIMO (Canadian Timothy Model). In this paper, we describe the digestibility module, which features the cell wall (CW) digestibility and CW concentration for each of the plant morphological components derived from the growth module of the model. The model parameters were calibrated to key model attributes: concentration and digestibility of CW in leaves, stems, and forage and dry matter (DM) digestibility of leaves, stems, and forage. Calibration measurements were taken weekly on timothy primary growth in four different years at one location (Fredericton, NB, Canada). The model satisfactorily fitted the measured values with root mean square errors of estimation (RMSE) of 0.051 g g−1 DM for forage CW concentration, 0.026 g g−1 CW for forage CW digestibility, and 0.018 g g−1 DM for forage DM digestibility. The leaf and stem CW concentration (RMSE ≤ 0.044 g g−1 DM), CW digestibility (RMSE ≤ 0.019 g g−1 CW), and DM digestibility (RMSE ≤ 0.018 g g−1 DM) were also calculated satisfactorily by the model. The CATIMO model is a promising tool because of its mechanistic and flexible approach and the good agreement between measured and simulated values.