pedon

Chilean volcanic soils are known to contain large amounts of organic matter (OM) and amorphous (e.g., allophanic) clay. Here, we test the hypothesis that Al, rather than clay content and climatic conditions, is the most important factor for OM levels in volcanic soils. This was achieved by compiling a total of 225 pedons from two national-wide datasets of south-Central Chilean soils sampled in the first 20 cm depth. All selected soils are of volcanic origin, previously under native Nothofagusforest and now used as pasture or arable land. The relationships between soil organic C (from now soil C) and environmental and soil characteristics (clay-allophane, Al content) were analysed by simple and multiple linear regression analyses. Soils classify as Alfisols, Andisols, Inceptisols and Ultisols. Al was extracted by KCl (Al k), acid ammonium acetate (Al a) and acid ammonium oxalate (Al o). The simple regression models showed that Al a correlated best (R 2 = 0.52) with soil C variations for the four soil orders studied, while Al k (R 2 = 0.08) and Al o (R 2 = 0.17) were poorly correlated in all soils types. Especially in Inceptisols, Al a was highly correlated with soil C (R 2 = 0.88). Clay content, and hence allophanic content, was poorly correlated with soil C (R 2 = 0.14), as was the mean annual precipitation (R 2 = 0.21) and temperature (R 2 = 0.15). These patterns were supported by the multiple regression analyses. Results therefore support the idea that Al is the principal factor for immobilization of OM in acid volcanic soils. As ammonium acetate extractable Al at pH 4.8 correlated well with OM, and as this is a rarely used method to interpret pedogenic processes, this extraction method warrants further attention.

Chilean volcanic soils are known to contain large amounts of organic matter (OM) and amorphous (eg, allophanic) clay. Here, we test the hypothesis that Al, rather than clay content and climatic conditions, is the most important factor for OM levels in volcanic soils. ...

Land use and soil management affects soil organic carbon (SOC) pools, chemical composition of stabilized SOC fractions, and the depth distribution. No-till production of corn (Zea mays L.) is a recommended management practice that reduces soil losses and increases SOC concentration, but the scientific knowledge of the mechanisms of C sequestration and protection is scanty. Therefore, the objective of this research was to compare the SOC pool, C pool in fine roots, and chemically separated C fractions with depth in three pedons from the same soil series: (i) meadow converted from no-till corn in 1988 (Meadow), (ii) continuous no-till corn since 1970 (NT); and (iii) continuous no-till corn with beef cattle manure since 1964 (NTm) at the North Appalachian Experimental Watershed near Coshocton, Ohio. The SOC pool (Mg ha − 1) from 0-69 cm was the highest in NTm (76.2) and progressively smaller in NT (49.3) and Meadow (46.6) pedons. The SOC concentrations and pool sharply decreased with depth, but were always more in NTm than NT soil. Fine root C pool (Mg ha − 1) was much larger in the pedon with perennial vegetation (Meadow, 1.28) than in those under corn (NT, 0.21; NTm, 0.09). The pool of chemically separated C fractions and their depth distribution varied depending on the separation technique. The amounts of C preferentially bound to soil minerals in 0-69 cm depth were comparable among pedons, as indicated by treatment with HF to release mineral-bound SOC. The NTm pedon had a larger pool of recalcitrant non-hydrolyzable C (58.4 Mg ha − 1), as indicated by HCl treatment. The Meadow pedon stored the smallest pool (3.4 Mg ha − 1) of oxidisable C, as was indicated by treatment with disodium peroxodisulfate (Na 2 S 2 O 8). The relationship between chemically separated C fractions and turnover time of SOC at depth, however, warrants further studies. Nevertheless, the results indicate that no-till corn with added manure has a high potential for C sequestration by increasing the size of the SOC pool in the subsurface horizons.

Scope of the journal The primaryintentionof the joumal is to stimulatewide interdisciplinary cooperationand understand-' ing amongworkers in the differentfields of pedology.Therefore, the joumal tries to bring together papers from the entire field of soil research, rather than to emphasize any one subdiscipline. Interdisciplinary work shouldpreferablybe focused on occurrenceand dynamiccharacterizationin space andtimeof soilsin the field.