Coupling the STICS model and CATIMO equations to simulate the growth and nutritive value of alfalfa

Abstract

Although alfalfa (Medicago sativa L.) is one of the most cultivated perennial forage crops in the world, little information exists on the possibility of simulating both its growth and nutritive value. Our objectives were to evaluate and improve the performance of the STICS 10.0.0 model in simulating the biomass and leaf area index (LAI) of alfalfa grown in eastern Canada, and the performance of the equations derived from the Canadian timothy model (CATIMO) to predict three attributes of alfalfa nutritive value: neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFd), and in vitro true digestibility (IVTD) of the dry matter with STICS outputs. STICS was first calibrated, and its performance to simulate the growth of two alfalfa cultivars in spring and summer was evaluated. Leaf and stem biomass outputs from STICS were then used to calibrate and evaluate the CATIMO nutritive value equations. Twenty-four datasets were used from two cultivars (Oneida VR and Calypso) and five sites in eastern Canada. STICS succeeded in simulating the aboveground biomass (normalized root mean square error [NRMSE] ≤ 27%) and the LAI (NRMSE ≤ 21%). Taproot biomass and aboveground biomass N concentration were also sufficiently well simulated. The new parameterization and modifications of the CATIMO equations allowed the model to accurately simulate the alfalfa nutritive value with NRMSE under or equal to 15%, 11%, and 5% for NDF, NDFd, and IVTD, respectively. STICS, combined with the improved nutritive value equations, is therefore suitable to simulate alfalfa growth and nutritive value in future studies.