Long-term Impact of Land Use Change on Soil Elemental Composition

Long-term impact that land use change exerts on soil elemental pool is evaluated in the Coastal Plain in northern Delaware. Two soil profiles of forest and agricultural land, which are in close proximity but under different land use types at least for last hundred years, are studied. The forest soil is used as a reference soil unaffected by agricultural activity. We determined major and minor elemental compositions, soil texture, exchangeable cations, and total carbon and nitrogen contents of the soils. Using geochemical mass balance model, we calculated the fractional mass losses of major oxides relative to the parent material. Zr was used as a weathering conservative index element. Nutrient elements (Ca, Mg, Na, K, and P) are significantly (by 20%) less depleted in the agricultural soil than those in the forest soil. The exchangeable portions of those elements in the total elemental pools are greater by 100%-300% in the agricultural soil, indicating that the inputs of those elements occurred through fertilizer and manure. In contrast to the inorganic nutrient elements, the forest soil harbors greater amount of total carbon and nitrogen in the top soil than the farmland soil by 80% and 60%, respectively. This indicates the different magnitude of inorganic nutrients cycled through organic matter in at the two soils. In addition to detailing the elemental chemistry and mineralogy of parent material to solidify our geochemical mass balance approach, we are quantifying (1) the accumulated masses of the fertilizer-driven nutrient elements, (2) the losses of those elements by chemical weathering, and (3) the losses of those elements via biomass harvest, which will allow us to understand the long-term impact of agricultural activity on soil geochemistry.