Model predicting dynamics of biomass, structure and digestibility of herbage in managed permanent pastures. 1. Model description

Abstract

To investigate seasonal and annual interactions between management and grassland dynamics, a simple mechanistic model of the dynamics of production, structure and digestibility in permanent pastures was constructed. The model is designed to respond to various defoliation regimes, perform multiple-year simulations and produce simple outputs that are easy to use as inputs for a model of ruminant livestock production. Grassland communities are described using a set of average functional traits of their constituent grass groups. The sward is subdivided into four structural compartments: green leaves and sheath, dead leaves and sheath, green stems and flowers, and dead stems and flowers. Each compartment is characterized by its biomass, age and digestibility. Only above-ground growth is modelled, using a light-utilization efficiency approach modulated by a seasonal pattern of storage and mobilization of reserves. Ageing of plant parts is driven by cumulative thermal time from 1 January and by biomass flows. Age affects senescence, abscission and digestibility of green compartments and, therefore, the quality of green leaves and stems can increase or decrease over time in relation to net growth and defoliation dynamics. The functional traits having the greatest impact on model outputs are seasonal effects, period of reproductive growth and effects of temperature on photosynthetic efficiency.The functional traits of the grass groups were parameterized for temperate pastures of the Auvergne region in France. The other model inputs are few: proportion of functional groups, basic weather data (incident photosynthetically active radiation, mean daily temperature, precipitation and potential evapotranspiration) and site characteristics (nitrogen nutrition index, soil water-holding capacity). In the context of a whole-farm simulator, the model can be applied at a field scale.

Model predicting dynamics of biomass, structure and digestibility of herbage in managed permanent pastures. 2. Model evaluation

“…To improve prediction and further understanding of the dynamics of managed grasslands at the field and farm scales, a mechanistic model of the dynamics of production, structure and digestibility of herbage in permanent pastures was constructed (Jouven et al. , 2006).…”

Self-insurance and multi-peril grassland crop insurance: the case of French suckler cow farms

“…Values are set according to estimations made on real suckler-cow farms (Mosnier et al, 2014) (aj_harv ¼ −10 percent of total grassland area for C1; −5 percent for C1 and +5 percent for C3). When grass use is delayed to the following period, there are losses due to average ageing process and to environmental conditions (abs) ( Jouven et al, 2006). At the beginning of the year, the stock of standing grass is assumed to be null:…”

Do plant functional types based on leaf dry matter content allow characterizing native grass species and grasslands for herbage growth pattern?

“…Indeed PFT compositions of the community respond both to nutrient availability that is well known (Wilson et al 1999 for example) and to defoliation management that can have complex effects due its four dimensions (frequency, intensity, timing and extent), (Grubb 1998). Other criteria such as sward nutrient index will perform much better (Duru et al 1994;Jouven et al 2006). However, plant functional approach allows the identification of key plant features such as phenological stages that are essential for modelling the differences in herbage growth patterns between plant communities as pointed out previously (McCall and Bishop-Hurley 2003).…”