A paired watershed study consisting of agroforestry (trees plus grass buffer strips), contour strips (grass buffer strips), and control treatments with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation was used to examine treatment effects on runoff, sediment, and nutrient losses. During the (1991-1997) calibration and subsequent three-year treatment periods, runoff was measured in 0.91- and 1.37-m H-flumes with bubbler flow meters. Composite samples were analyzed for sediment, total phosphorus (TP), total nitrogen (TN), nitrate, and ammonium. Calibration equations developed to predict runoff, sediment, and nutrients losses explained 66 to 97% of the variability between treatment watersheds. The contour strip and agroforestry treatments reduced runoff by 10 and 1% during the treatment period. In both treatments, most runoff reductions occurred in the second and third years after treatment establishment. The contour strip treatment reduced erosion by 19% in 1999, while erosion in the agroforestry treatment exceeded the predicted loss. Treatments reduced TP loss by 8 and 17% on contour strip and agroforestry watersheds. Treatments did not result in reductions in TN during the first two years of the treatment period. The contour strip and agroforestry treatments reduced TN loss by 21 and 20%, respectively, during a large precipitation event in the third year. During the third year of treatments, nitrate N loss was reduced 24 and 37% by contour strip and agroforestry treatments. Contour strip and agroforestry management practices effectively reduced nonpoint-source pollution in runoff from a corn-soybean rotation in the clay pan soils of northeastern Missouri.
Abstract. The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (I-12kgN ha-' yr-') are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1 -5 kg N ha-' yr-I), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 3040% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from z lo-160 kg N ha-' yr-' in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.The existing information on N inputs is deficient in several areas: -more intensive studies of total atmospheric deposition, especially of dry deposition, are needed over a wide range of ecosystems; -additional studies of symbiotic fixation are needed that carefully quantify variation over space and time, examine more factors regulating fixation, and focus upon the availability of N and its effects upon productivity and other nutrient cycling processes; -process-level studies of associative N-fixation should be conducted over a range of ecosystems to determine the universal importance of rhizosphere fixation; -further examination of the role of free-living fixation in wood decomposition and soil organic matter genesis is needed, with attention upon spatial and temporal variation; and -investigations of long-term biogeochemical impacts of these inputs must be integrated with process-level studies using modem modelling techniques.
Growth increments of eastern red‐cedar (Juniperus virginiana L.) from sites in the Pb mining district of southeast Missouri were subjected to multielemental analysis. Three chronologies, two of Pb and one of Cd, were constructed from heartwood growth increments of 27 trees on sites in the mining district and on control sites. No significant increases in Pb and Cd were found in growth increments of trees on control sites. Lead in the xylem of trees growing in acid soils of the mining district increased from 3.1 µmol kg−1 in growth increments formed before 1900 to 7.8 µmol kg−1 in increments formed after 1900. Cadmium was detected in 46% of the wood formed after 1900 vs. 3% of the wood formed before 1900. Lead and Cd were found only in wood grown on acid soils (pH <4.6) and not in wood grown in more basic soils. Lead and Cd concentrations in growth increments are found to be highly correlate with Pb production. Lead in sapwood was also found to correlate with soil pH on acid sites in both the mining district and in the control sites.
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