The Use of Thermal Time to Describe and Predict the Growth and Nutritive Value of Lolium perenne L. and Bromus valdivianus Phil

Abstract

The thermal time, expressed in accumulated growing degree-days (AGDD), was used as a predictor to describe and simulate the independent growth of two pasture crops, Lolium perenne L. and Bromus valdivianus Phil. Two sinusoidal models (four-parameter Logistic and Gompertz) were applied to the growth variables (total leaf blade length per tiller—LBL, and accumulated herbage mass—AHM). The nutritive value of pastures was predicted and modeled using regression equations (linear and quadratic), depending on each nutrient. Data for modeling were collected from a two-year study, in which LBL, AHM, and nutritive value variables for L. perenne and B. valdivianus pastures were measured at three-day intervals. Defoliation was determined according to the AGDD, such that the swards were defoliated at 90, 180, 270, 360, and 450 AGDD. The Logistic and Gompertz models presented similar values for the growth rate (GR) parameters, superior asymptote (Asup), inferior asymptote (Ainf), and point of maximum growth (Pmax). In both species, the maximum growth was 260 AGDD. The GR was similar for both species in different seasons of the year, but the maximum AHM varied, with B. valdivianus presenting a higher value (+1500 kg DM ha−1) than L. perenne during the spring. The regressions accurately described the nutritive value, demonstrating a positive linear relationship between the AGDD and concentrations of neutral and acid detergent fiber (NDF, ADF), an inverse linear relationship with crude protein (CP), and a quadratic relationship with metabolizable energy (ME) and water-soluble carbohydrate (WSC) concentration.

Modeling the Daily Dynamics of Grass Growth of Several Species According to Their Functional Type, Based on Soil Water and Nitrogen Dynamics: Gras-Sim Model Definition, Parametrization and Evaluation

“…Several models already address the grass growth dynamics. Most of them simulate monospecific or speciesdominated grasslands, in particular that of the perennial ryegrass (Lolium perenne), under cutting conditions [15][16][17] or grazing by taking into account the impact of the grazing process on the sward [18][19][20][21].…”

Climate Factors Contribute to Grassland Net Primary Productivity

“…In the semi-arid regions, the paper focused more on the response of natural grasslands to the increasing climatic constraints, fluctuations in temperature and precipitation. The approaches chosen were empirical [1][2][3] providing evidence for dose-response relationships for management effects and environmental changes. These are essential to derive parameters for process-based modelling as shown by Giannitsopoulos [4], as well as for understanding ecological phenomena and implementing observed changes in functional groups [3] and functional types [5].…”

“…Calvache et al [1,2] provide the evidence for optimising yield and quality as a function of off-take intensity for mixed grazing and mowing systems, comparing an indigenous to the widely used European grass forage species (Lolium p.). Giannitsopoulos and colleagues demonstrate that the expanded LINGRA model can emulate such effects on production and composition once calibrated for high-performance grassland [4].…”