02 Contents Frame
tải về 0.57 Mb. Chế độ xem pdf
|
40 2019 ND-CP 413905
| The CENTURY model, capturing both plant production and environmental
concerns related to nutrient budgeting (Parton et al., 1994; Parton & Rassmussen 1994), was developed to model the movement of soil organic matter and nutrient dynamics in the environment using plant-soil relationships for different types of ecosystems including grasslands, agricultural lands, forests and savanna. CENTURY simulates the growth of various crops, grasses and trees. Different crop, grass and forest systems are distinguished by varying the parameters that control maximum growth rate, C allocation among plant parts and the C/N ratios of plant parts. Parameters in the equations that account for shading, water and temperature limitations, maximum plant growth rate, ranges of C/N ratios for plant compartments, etc. can be adjusted to reflect the physiological properties of various vegetation types and particular species of grasses, crops or trees. Biomass can be removed or transferred to other organic matter pools such as litter by disturbance events such as harvesting, grazing, plowing, burning, clear cutting. Disturbance events affect both the quantity and nutrient concentration of litter that supplies the soil organic matter pool. The CENTURY model uses inputs of precipitation, maximum and minimum temperature, soil type, and current as well as historical land use information to simulate changes in C, N, P, S and biomass production on a monthly time step. CENTURY includes submodels for plant growth, decomposition of dead plant material and SOM, and soil water and temperature dynamics. Plant growth is limited by soil water content, temperature, and nutrient availability. Carbon and nutrients are allocated among leaf, woody, and root biomass based on vegetation type and nutrient availability. Transfer rates of C and nutrients from dead plant material to the soil organic matter and available nutrient pools are controlled by the lignin concentration and C/N ratio of the material, decomposition factors based on temperature and soil water, and soil physical properties related to texture. Three soil organic matter (SOM) pools are considered in the SOM submodel: active SOM, slow SOM and passive SOM. The active SOM pool has a rapid turnover time (0.5–1year), and includes dead plant material with low C/N ratios and low proportions of lignin, microbial biomass and the highly labile by-products of microbial metabolism. Active SOM is converted into CO 2 , inorganic forms of nutrients and slow SOM. The slow SOM pool has intermediate turnover rates (10–50 years), and includes material with high C/N ratios and high lignin contents and the microbial by-products that are moderately resistant to further decomposition. The passive SOM pool has a very slow turnover rate (1000–5000 years), and consists of material that is extremely resistant to further breakdown. An important product of decomposition is CO 2 . Finer textured soils retain more organic matter in stable forms due to chemical and physical protection. The available nutrient pool (NO 3 , NH 4 , P, S) is supplied by decomposition of SOM, biological N fixation, and external nutrient additions such as fertilization and atmospheric N deposition. The proportions of SOM in the respective pools, and soil water, temperature, and texture determine the rate of nutrient supply from decomposition. Available nutrients are distributed among soil layers under the Annex 3 – Tools for land evaluation 97 assumption that the concentrations of mineral N and SOM are highest near the soil surface and decline exponentially with depth. The CENTURY model is an integrated model that captures. Other models that deal with carbon sequestration on agricultural land are CQESTR (Rickman et al., 2001) and the Roth-C model (Coleman and Jenkinson 1999). tải về 0.57 Mb. Chia sẻ với bạn bè của bạn:
|