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{sub}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{sub}(il)), active inorganic P (P{sub}(ia)), stable inorganic P (P{sub}(is)), fresh organic P (P{sub}(of)), and more stable organic P ({sub}(oh))- The major model modifications made were: (1) initialization of P{sub}(il) from the Finnish soil test results (ammonium acetate extractable P, P{sub}(AAC))> (2) initialization of P{sub}(ia) and P{sub}(is) from P{sub}(il), assuming equilibrium; (3) revision of the P availability factor (F{sub}l), which regulates the flow between P{sub}(il) and P{sub}(ia); and (4) calculation of the initial values of P{sub}(oh) from soil organic carbon content. These modifications aimed to improve simulation of P{sub}(il) on the basis of data obtained from soil testing. Proper simulation of changes in P{sub}(il), reflected by the soil test P (P{sub}(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{sub}(AAC) at annual P application rates of 0 and 30 kg ha{sup}(-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{sup}(-1).