The fate of phosphorus during pedogenesis

The soil organic matter (SOM) pool encompasses plant, animal, and microbial residues in all stages of decay and a diversity of heterogeneous organic substances intimately associated with inorganic soil components. The soil microbiota and fine roots may also be considered part of the SOM pool. The turnover of the different SOM components varies continuously due to the complex interaction of biological, chemical, and physical processes in soil. The complexity of SOM and its importance to soil fertility have challenged generations of soil scientists, and numerous studies, of which some date back more than two centuries (see historical review in Kononova, 1961), have covered a vast array of aspects of SOM.

Physical Fractionation of Soil and Organic Matter in Primary Particle Size and Density Separates

The transformations of soil organic phosphorus are described and organized in a conceptual model. Microbial uptake of P and its subsequent release and redistribution play a central role in the soil organic P cycle. Interactions with soil minerals and stabilization of organic matter and associated P in organo-mineral complexes determine the persistence and buildup of organic P through soil development, in different ecosystems and under varying management. An understanding of organic P turnover in soils will greatly aid assessment of P fertility in many agricultural and native systems.

Dynamics of soil organic phosphorus

Phosphorus (P) is essential for plants and animals because of its role in vital life processes, such as in photosynthesis in plants and energy transformations in all forms of life. It also has a significant role in sustaining and building up soil fertility, particularly under intensive systems of agriculture.

Chemistry of Phosphorus Transformations in Soil

This review concentrates on two sources of phosphorus input to terrestrial ecosystems: release by weathering of rock and inputs from the atmosphere. The few direct estimates of P release by weathering give rates from 0.05-1.0 kg P ha{sup -1} yr{sup -1}; however less direct evidence suggests that rates up to 5 kg ha{sup -1} yr{sup -1} may occur. Total P input from the atmosphere collected by funnels can range from 0.07-1.7 kg ha{sup -1} yr{sup -1}. Input to some vegetation may be substantially increased by the canopy trapping suspended fine particles. Major sources of atmospheric P include fine soil particles, pollen, and burning of plant material, coal and oil. Their amount and relative importance varies greatly from place to place. The wide variation in P inputs between sites results in inputs being greater than losses at some sites but less than losses at others. This is likely to have major longterm ecological importance.

T. W. Walker

Papers

Fractionation of Phosphorus in Two Alluvial Soils and Particle-Size Separates