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Data on the total nutrient content of soils is essential for assessing potential fertility and is fundamental to environmental and edaphogenetic studies. The aim of this paper was to measure Cu, Zn, Fe y Mn in soils of the Chaco Pampean Plain in Argentina using the simultaneous acid nitric (HNO3 4 M) extraction procedure (called pseudototal) to infer geochemical background and geochemical baseline data by analysing surface and subsurface samples. The results can be related with other edaphic features such as organic carbon, acidity, salinity and carbonates. Average values of 11.3 to 19.2 mg Cu kg-1, 29.4 to 61.5 mg Zn kg-1, 285 to 626 mg Mn kg-1 g-1 and 9 to 19.9 g Fe kg-1 were found at a soil depth of 0-60 cm, falling within the range reported in worldwide literature. The lowest values were found in sandy soils. The values at a soil depth of 0-20 cm were 17 mg Cu kg-1, 55 mg Zn kg-1, 562 mg Mn kg-1 and 16 g Fe kg-1 in loessic and loam loessic soils and 12 Cu kg-1, 36 mg Zn kg-1, 347 mg Mn kg-1 and 11 g Fe kg-1 in loam sandy soils. The textural difference between loessic and sandy soils reflects different background values for the four elements studied, the lowest values corresponding to sandy soils. Multiple regression analysis included Fe and Mn as the main variables to explain the amounts found for each of the four elements at each depth which is related to the high affinity between transition metals and their tendency to co-precipitate as low cristallinity oxides.The second variable in most of the models for the studied elements was organic carbon, confirming the importance of organic matter as a primary source of these micronutrients. [ABSTRACT FROM AUTHOR]

Information about the effects of crop residues on soil parameters in no-tillage systems is not abundant in Argentina because the relative recent adoption this practice. Moreover, most of the available research to date refers to the humid Pampa region. In contrast, information on the semi-arid region is very scarce, despite the fact that an increase in cover stubble is particularly useful in water-limited soils. In this paper we report a long-term evaluation (5 to 10 years) of no-tillage practices on: a) chemical (soil organic matter -SOM, total N and NO3-N) and biological (microbial biomass and activity) soil characteristics, and b) quantity and chemical quality of soybean residues in monoculture and soybean-corn rotation. Research was conducted at Manfredi INTA Experimental Station in semi-arid, central Argentina(31°49' S and 63°46' W). Soils under no-tillage system had higher SOM and total N content compared with control (conservation tillage with chisel plow) in soybean monoculture and soybean-corn rotations. The observed difference increased with time (10 and 20% at 5 and 10 years, respectively). Nitrate content, and microbial activity and biomass showed high variability in the measurement periods, depending on climatic condition at the sampling date. Stubble cover was greater in the corn-soybean rotation with corn as preceding crop (2473.9 g m-2) than in soybean monoculture (1035.7 g m-2)). The stubble non-identifiable fraction was very significant in all treatments (ranging between 2-10 t ha-1), which would favor new surface organic soil formation. The soybean-corn rotation with soybean as preceding crop showed the lowest values in all chemical parameters, particularly in soluble compounds (nitrate, ammonium and soluble carbon). Contrarily to what is usually assumed, our results suggest that nutrient release from long-term stubble may become a significant nutrient source for the crops. Therefore, this nutrient source should be considered when evaluating crop fertilization requirements. [ABSTRACT FROM AUTHOR]