SIMULATING PROCESSES OF SOIL PHOSPHORUS IN GEOLOGICALLY YOUNG ACIDIC SOILS OF FINLAND

摘要

To properly simulate phosphorus (P) loading from agricultural land to waters, changes in soil P status and processes affecting soil P have to be described adequately. For practical reasons, a model has to rely on data that are commonly available. In this study, the P submodel of the ICECREAM model, based on the CREAMS, GLEAMS, and EPIC models, was adapted to simulate young acidic soils, which prevail in Finland. These soils have a high P sorption capacity, plenty of inorganic P in a non-reactive apatitic form, and the organic matter content (O _r ) in the plow layer is commonly about 5%. The model was modified mainly on the basis of 12 long-term fertilization experiments and tested on three other soils. The P pools considered were labile P (P _il ), active inorganic P (P _ia ), stable inorganic P (P _is ), fresh organic P (P _of ), and more stable organic P (P _oh ). The major model modifications made were: (1) initialization of P _il from the Finnish soil test results (ammonium acetate extractable P, P _AAc ); (2) initialization of P _ia and P _is from P _il , assuming equilibrium; (3) revision of the P availability factor (F _l ), which regulates the flow between P _il and P _ia ; and (4) calculation of the initial values of P _oh from soil organic carbon content. These modifications aimed to improve simulation of P _il on the basis of data obtained from soil testing. Proper simulation of changes in P _il , reflected by the soil test P (P _AAc ), is critical since it regulates the level of dissolved P in runoff water. After the modifications, the model was able to predict changes in P _AAc at annual P application rates of 0 and 30 kg ha -1 in cereal cropping, but could not fully cope with a large surplus of P resulting from an annual rate of 60 kg P ha -1