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DIVISION S-8—NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

Predictive Mechanistic Model of Soil Phosphorus Dynamics with Readily Available Inputs

^a Dep. of Agrochemistry, All-Russian Institute of Agriculture and Protection of Soil from Erosion, Karl Marks Str., 70-b, Kursk, Russia, 305040
^b Horticulture Research International, Wellesbourne, Warwick, CV35 9EF UK
^c Dep. of Biosystems Engineering and Environmental Science, Univ. of Tennessee, 2505 E.J. Chapman Drive, Knoxville, TN 37996-4531

^* Corresponding author (ammonst{at}utk.edu).

Fertilizer and manure P applications together with cropping practices can have a lasting effect on soil fertility and can result in pollution of waterways. This study was aimed at providing a general model for the long-term changes in soil P extracted with conventional tests. The model maintains three active pools of soil P: extractable soil P (X), absorbed P that is not extractable but interchanges reversibly with X (Y), and mineral P that provides solubility-product type buffering of X (P_buffer). There is also an input for the net P addition. Equations derived from the model define most of the published patterns of response of X found in long-term field experiments. They underpin a dynamic version of the model that permits annual inputs and calculates the time-course of the various P pools. A method was devised for calibrating the dynamic version from measurements that are usually made in long-term experiments. Models calibrated in this way gave good fits to the data from six soils from four countries. Values of the coefficients indicated that solubility product buffering had a decisive influence on the P economy of some but not all soils. The model gave predictions of X that were in good agreement with measurements in three long-term experiments that were entirely independent of those used for calibrating the model. Other possible methods of calibration are discussed. The model concisely represents key factors affecting the dynamics of X over the long term and has both interpretative and predictive value.

Abbreviations: K1, rate constant for conversion of X to Y • K2, rate constant for conversion of Y to X • K3, rate constant for conversion X to P_buffer • K4, rate constant for conversion of P_buffer to X • P_balance, net annual addition less removal of P • P_inert, the intercept of the linear relationship between Y_total and X • P_buffer, soil P that provides long-term buffering • R, fraction of P_balance that is added to X • subscript st.art., level of soil P created by fertilizer and manure application • subscript st.st., steady stationary state • X, soil P extracted in conventional tests • Y, unextractable P that interchanges with X • Y_total, the total amount of all forms of soil P

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