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Asseng et al. (2015): 
Rising heat reduces global wheat production. Nature Climate Change 5 (2), 143–147.


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MONICA describes processes in the soil–plant system and the energy and matter exchange with the hydro- and atmosphere. Using daily weather data, it calculates the soil temperature for single discrete layers in the soil. The movement of water in the soil is modelled using a capacity approach. This approach assumes that water that cannot be stored in a soil layer will be passed on to the adjacent layer below. The layer’s storage capacity and its percolation rate are governed by its texture and soil organic matter content. Evaporation and water uptake by the root influence the water budget. If groundwater is accessible capillary water can rise into the root zone.

Moving soil water carries nitrates. They originate from organic matter turn-over, appearing first as ammonium (ammonification) which is later turned into nitrates (nitrification). If oxygen is deficient, nitrate can be transformed into atmospheric nitrogen (denitrification), a process during which the greenhouse gas N2O is produced. The microorganisms facilitating these processes and producing CO2 from their metabolism are also simulated. When organic fertilisers are applied, gaseous NH3 is set free. Furthermore, also urea fertiliser hydrolyses in the soil and releases NH3.

The crop‘s biomass increases according to the daily radiation and temperature. A target and a critical nitrogen concentration are calculated for the plant tissue. The first serves the calculation of nitrogen uptake from the soil, while the second is used to determine nitrogen deficiency. In the latter case, similar to drought stress, the crop’s daily growth increment will be reduced. In daily time steps  the root grows into depth. The calculated root biomass is distributed to the discrete soil layers accordingly. The calculation of water and nitrogen uptake by the plant considers this distribution and consumes from the respective soil layers. 

At harvest, crop residues remain. They are decomposed and contribute to soil organic matter pools, nitrogen mineralisation and CO2 release. Every organic material has its own properties which determine its decay. That way a lettuce leaf will be mineralised much faster than wheat straw. Currently, MONICA is able to simulate eight different crops.

Last Updated on Monday, 20 February 2012 10:03