Modeling Tiller Density, Growth, and Yield of Mediterranean Perennial Grasslands with STICS

Abstract

A generic crop model (STICS) was adapted (STICS–Grassland) to model growth, yield, and environmental impacts of grasslands in France. It is a semimechanistic model combining equations of physiological processes and mathematical relationships between processes in a daily time step. The Information et Suivi Objectif des Prairies (ISOP; Grassland Information and Objective Survey) application was developed to estimate and map the real‐time status of grass growth and forage production in the 200 forage regions of France, to help decision makers anticipate forage availability in case of severe deficits. Initially, the model could not simulate long, severe droughts typical of Mediterranean regions when plant and tiller densities are significantly reduced. A tiller density module models the dynamics of tiller death during droughts. Since STICS is based on the concept of a mean plant (tiller) covering the whole field, variability was introduced through a γ law distribution of transpiration deficit by tiller, a threshold value imposing desiccation, and death to tillers reaching this level. Its second part generates incomplete or total recovery of tiller density through new tillering in the next wet season. Species and contrasting groups of cultivars within species can be characterized with a limited number of parameters.

Key challenges and priorities for modelling European grasslands under climate change

“…In addition, perennial species in these systems undergo a period of summer dormancy due to harsh conditions in the summer months. Although some models, such as STICS (Ruget et al, 2009) consider summer dormancy in perennial species, relatively few models have focussed on these types of grassland, despite the expected negative impact of climate change on Mediterranean regions of Europe (Iglesias et al, 2012). In this case, the systems in question differ between regions, but differences may also cut across regions.…”

Combined use of FORMOSAT-2 images with a crop model for biomass and water monitoring of permanent grassland in Mediterranean region

“…-STICS has been coupled with various remote sensing data in the past, for different applications (Di Bella et al, 2004;Guerif et al, 2007;Varella et al, 2010) and -it has been developed and validated for grasslands by our team (Ruget et al, 2002(Ruget et al, , 2008(Ruget et al, , 2009.…”

“…However, it should be noted that the grassland age being very different between some fields (more than 80 years apart), this fact has led to a spatial variability of organic nitrogen in the soil. Thus the initial parameters linked to nitrogen in the soil were defined according to the mean values measured on the reference field and the expert knowledge, taking into account standard values found in the literature (Ruget et al, 2009). Figure 6 summarizes the approach proposed to combine STICS crop model and high spatial and temporal resolutions FORMOSAT-2 data to assess yield and water budgets at regional scale.…”

“…Three harvests are made between May and September. Some crop models propose a generic approach where the plant development (representing mainly by the Leaf Area Index, LAI), is modelled with functions depending on temperature, photoperiod and chilling needs (Ruget et al, 2009). Other approaches propose combining decision models and a biophysical models to take into account the response to irrigation (Mailhol and Mérot, 2008).…”

“…Some approaches proposed classifications to define the main agricultural practices performed in a given region. For example, in the ISOP system (Information et Suivi Objectif des Prairies), which is an operational application of the crop model (STICS) to estimate and map the real-time status of grass applied at the France scale (Ruget et al, 2006(Ruget et al, , 2009, the country is divided into approximately 200 small forage regions (∼2500 km 2 each). In each region, representative classes of grassland were defined by combining the most frequent soil types, the common types of grassland (in terms of management, combinations of cutting-grazing and N fertilization) resulting in 25 typical pasture combinations.…”