Changes in major solute chemistry as water infiltrates soils: Comparisons between managed agroecosystems and unmanaged vegetation.

摘要

This study examined chemical changes in water residing in sandy loam soils on glacial drift. Soil solutions were collected over several years from tension samplers beneath 10 treatments at the Kellogg Biological Station's Long Term Ecological Research site, including deciduous forest, conifer plantations, successional ecosystems, and row crops under varying intensity of agronomic management.; Soil solutions were enriched in solutes relative to precipitation. Nitrate, calcium, magnesium, and alkalinity differed most markedly among treatments. Early and late successional communities as well as a rapidly growing perennial poplar plantation had ionically dilute solutions with low nitrate concentrations. Agricultural treatments were significantly enriched in major solutes relative to precipitation.; Soil solution concentrations of nitrate indicated that the zero input (organic) row-crop treatment had lower potential nitrate leaching than the other row crop treatments. The no-till treatment had the next lowest nitrate concentrations, but had high variance in concentrations, perhaps due to its high inputs of nitrogen.; Losses of calcium and magnesium were significantly and positively correlated with nitrate (r = 0.9 and 0.8, respectively) across treatments, pointing to the importance of nitrification as a source of protons that release divalent cations from the soil exchange complex. This in turn causes both the potential pollution of ground and surface waters and the concomitant degradation of the soil through the loss of important macronutrients.; Native carbonate minerals are absent from the upper 1--1.5 m of these soils but are abundant at depth. Liming is necessary to counteract acidification by agriculture. Carbonate minerals, whether native or as lime amendments, can either release or sequester carbon dioxide as they dissolve, depending on pH. Soil solution chemistry suggests that dissolution of lime in the agricultural row-crop treatments results in the net release of carbon in the form of carbon dioxide. This release was strongly and positively correlated with nitrate (r = 0.63), suggesting that biological nitrification is an important control on lime dissolution and thus carbon sequestration or release. However the overall C balance of liming could not be determined from this study because the samplers collected matric water as well as water infiltrating by gravity flow.