Quoted from: Huang, Yao, Yongqiang Yu, Wen Zhang, Wenjuan Sun, Shiliang Liu, Jun Jiang, Jinshui Wu, Wantai Yu, Yu Wang, and Zhaofang Yang. "Agro-C: A biogeophysical model for simulating the carbon budget of agroecosystems." Agricultural and forest meteorology 149, no. 1 (2009): 106-129. https://doi.org/10.1016/j.agrformet.2008.07.013 

      The carbon budget of an agroecosystem is simply defined as the difference between carbon into and out of the soil. Inputs are provided by crop roots, residue retention and other organic carbon sources such as organic manures, while output is due to soil heterotrophic respiration. Our biogeophysical model, Agro-C, consists of two submodels: Crop-C for simulating crop NPP and Soil-C for computing SOC (Fig. 1). Crop-C includes two main functional modules for photosynthesis and autotrophic respiration, which are driven by the environmental variables of temperature, solar radiation, soil moisture, and atmospheric CO2 concentration. Crop N uptake depends on the availability and demand for N. The availability of N is determined by the mineralization of the soil N pool and synthetic N application. Soil-C simulates the decomposition of organic carbon in soils with a first-order kinetics reaction. Organic carbon in soils comprises two parts: incorporated organic carbon from crop residues and/or other organic carbon sources, and SOC. Incorporated organic carbon is assumed to consist of two components, labile-C and resistant-C. The reaction rate of decomposition depends on the soil parameters of temperature, moisture, texture, and pH. Changes in SOC are determined by a balance between the loss of soil carbon and the sequestration of input organic carbon. Agro-C allows for the simulation of different crop rotations on macroscales with a daily step.

 

Fig. 1. Conceptual diagramme for modeling carbon processes within agroecosystems. Solid arrows represent mass flow between defined quantities and dashed arrows represent variables driving reaction rates.