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Trace metals, including heavy metals, can be harmful to the biota and human beings. This leads to study the accumulation of those elements in soils. In the Pampean region (Argentina) this knowledge is scarce. Our objectives were to (i) determine the trace metal concentration in soils of Buenos Aires City and agricultural areas, (ii) start to establish the soil trace metals baseline concentration, and (iii) find relationships between soil properties and those elements Topsoil samples were taken in Buenos Aires City and on farms along an arc 50 to 250 km away from the metropolis. All studied soils were Mollisols. Soil samples were analyzed for their cadmium (Cd), copper (Cu), zinc (Zn), chromium (Cr), cobalt (Co), lead (Pb), and nickel (Ni) contents by acid extraction. Soil properties were determined using standard methods. The soils of Buenos Aires City show the highest average concentrations of Cd, Cu, Pb, and Zn. The further the sampling sites were from Buenos Aires, the lower the metal concentration in the soils. Conversely, there were no differences in Co, Cr, and Ni concentrations from urban to the rural soils. There was a high variability in metal concentrations. We hypothetized that cars are the main source of contamination of Pb and Cd in the urban soils. The measured metals concentrations from rural areas, can be a basis from which to establish the background levels of those soils. Clay content was related to the concentrations of Cd, Cr, Ni. Pb, and Zn in soils.

The Rolling Pampa is the most important cropping region of Argentina, and its soils are subjected to degradation. No‐tillage has been proposed to replace the use of the moldboard plow to reduce soil C losses. The effects of no‐tillage and plow tillage with and without N fertilization (0 or 90 kg N ha−1) on C inputs and outputs of a Typic Argiudoll and on organic C level and density fractions were studied in a field experiment at the end of 15 yr under a corn (Zea mays L.)‐wheat (Triticum aestivum L.)‐soybean [Glycine max (L.) Merr.] rotation. Microbial biomass and the rate of organic C mineralization during laboratory incubations were also determined. Nitrogen fertilization had no significant influence on C emission in the field, soil organic matter level or microbial biomass and activity. The annual C budget was negative under both tillage systems, but no‐tillage lost about 0.7 to 1.5 Mg ha−1 yr−1 more C than did plow tillage. Carbon in the medium‐density fraction (density = 1.6‐2.0 g mL−1) of the 0‐ to 20‐cm soil layer was 30% higher (P ≤ 0.05) under no‐tillage. Light (density < 1.6 g mL−1) and heavy (density > 2.0 g mL−1) organic fractions, total C, and microbial biomass and activity in the 0‐ to 20‐ cm layer were not different in no‐tilled and plowed soils, despite different patterns of distribution with depth. The rates of organic C mineralization during laboratory incubations were the same for both tillage systems. We propose that, after an accumulation phase, soil under no‐tillage loses higher amounts of CO2‐C than under plowing. The use of no‐tillage would not significantly affect soil organic matter pools of the region in situations with low erosion losses.

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