Managed Land

Crop and Grass Production Model, description

AgroEcological Zones approach

Crop and grass production in IMAGE 2.4 uses the FAO AgroEcological Zones approach (FAO, 1978-1981a; FAO, 1978-1981b; FAO, 1978-1981c; FAO, 1978-1981d) to determine the potential distribution of different crops. When the length of the growing season is adequate for the crop group considered, a simple photosynthesis/respiration model is used to estimate potential productivity. This climate-related 'constraint-free, rainfed crop yield' accounts for light attenuation through the crop canopy using local climate. For a detailed description of the crop growth model, please refer to (Leemans and Born, 1994) and (Alcamo et al., 1998).

Soil conditions

The constraint-free, rainfed crop yield is adjusted for grid-specific soil conditions using a 'soil reduction factor' (ranging from 0.1 to 1.0). This factor is based on the methodology defined by the land evaluation computer system (LECS) (Wood and Dent, 1983) using the FAO soil map of the world (FAO, 1991). This reduction factor takes into account three soil-quality indicators:

1. nutrient retention and availability; 
2. level of salinity, alkalinity and toxicity;  
3. rooting conditions for plants (related to soil texture).                       

These indicators are assumed to be constant in time. The resulting crop productivity, called 'reduced potential productivity of crops', is used in the land-cover model.

Energy crops

A separate land-cover type is assigned to energy crops. Three energy crops are: sugarcane, maize and ‘wood’ (i.e. fast growing tree species in short rotation cycles like poplar and willow). This allows us to model: 

1. the interaction or even competition between the use of agricultural land for growing energy crops or food and feed crops; 
2. the consequences for the C-cycle.                       

The cultivation of energy crops aims to maximize the capturing of 'energy' (and thus carbon) instead of maximizing the yield of the 'edible' parts in food crop production. Parameter values in the carbon cycle model were therefore selected to mimic this orientation toward maximization of biomass production. The temperature / photosynthesis response curves were adapted for energy crops in order to match the energy crop yields with the crop growth model in different latitudinal belts.

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• to  external references
• to  MNP references