Improving the Science of Soil Change: A Proposal for the Earth Science Community.
Daniel D. Richter Jr., Duke University, Box 90328, Durham, NC 27708-0328
Long-formulated, highly significant questions remain unanswered about how humanity is transforming the Earth's soil and critical zone. These questions are complex as soil-forcing functions operate across multiple time and spatial scales: we require a concept of pedogenesis that telescopes over time scales of years, decades, centuries, and multi-millennia, and that fully recognizes the increasing prominence of humanity as a pedogenic factor. The general neglect of the human factor in pedogenesis combined with the notable absence of an active network of Long-Term Soil Experiments (LTSEs) directly limit understanding of decade-scale pedology, specifically how contemporary land management, climate, and pollution are transforming the Earth's soils over time scales of a few human generations. Models of soil dynamics are useful, but since soils are emergent systems that result from high-order interactions of physics, chemistry, and biota, models are no substitute for direct observations of soil change. Moreover, due to humanity's accruing history of impact on soil, on-going soil change is increasingly conditioned by historic human use. Pedogenic processes also operate on millennial to multi-millennial time scales, and soil change is determined by mineralogy, landform, long-running climates, and many generations of biota. For practical purposes, three time scales are proposed for understanding soil change: 1) multi-millennial, in which pedologic processes are determined by interactions of mineralogy, geomorphology, long-running climates, and countless generations of biota; 2) historic, in which the accumulation of human impacts may persist in effects from years to a few millennia, and 3) contemporary, in which soil changes are being driven by the active functioning of the current ecosystem. Observations of soil changes in acidification, phosphorus cycling, and Fe-redox cycling in a long-running soil experiment in southeastern North America illustrate the growing dominance of the human factor, the great need for an active network of long-term soil experiments, and the utility of viewing soil pedogenesis with three temporal perspectives: i.e., contemporary, historic, and multi-millennial.