Agricultural activities alter elemental budgets of soils and thus their long-term geochemical development and suitability for food production. This study examined the utility of a geochemical mass balance approach that has been frequently used for understanding geochemical aspect of soil formation, but has not previously been applied to agricultural settings. Protected forest served as a reference to quantify the cumulative fluxes of Ca, P, K, and Pb at a nearby tilled crop land. This comparison was made at two sites with contrasting erosional environments: relatively flat Coastal Plain in Delaware vs. hilly Piedmont in Pennsylvania. Mass balance calculations suggested that liming not only replenished the Ca lost prior to agricultural practice but also added substantial surplus at both sites. At the relatively slowly eroding Coastal Plain site, the agricultural soil exhibited enrichment of P and less depletion of K, while both elements were depleted in the forest soil. At the rapidly eroding Piedmont site, erosion inhibited P enrichment. In similar, agricultural Pb contamination appeared to have resulted in Pb enrichment in the relatively slowly eroding Coastal Plain agricultural soil, while not in the rapidly eroding Piedmont soils. We conclude that agricultural practices transform soils into a new geochemical state where current levels of Ca, P, and Pb exceed those provided by the local soil minerals, but such impacts are significantly offset by soil erosion.
Bibliographical noteFunding Information:
This study was financially supported by Critical Zone Observatory funding from National Science Foundation to K. Yoo and A.K. Aufdenkampe ( EAR-0724971 ), the Univ. of Delaware CANR seed grant to K. Yoo, and the Hatch fund from Agricultural Experimental Station to K. Yoo. Salary for J. Klaminder was financed by the Swedish research council (dnr. 2006-5063 ). XRD analysis of the Piedmont soil samples was carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. We also appreciate Nic Jelinski and anonymous reviewers for their comments that significantly improved the manuscript.
- Chemical weathering
- Geochemical mass balance
- Soil erosion