Norman Peinemann

Black carbon in grassland ecosystems of the world.

[1] Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific δ 13 C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14 C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13 C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m -2 ) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.

Soil organic matter particle size fractions in soils of the semiarid Argentinian pampas

Because the level of organic matter in soils can reflect the intensity of soil utilization, the present study was carried out with the aim of elucidating the precise effects of different soil management practices on total organic matter and its particle size fractions in soils of the semiarid pampa region. Surface samples of 52 entic Haplustolls under three different uses (24 under continuous cropping, 18 under rotation with grass leys and 10 virgin soils) were analyzed in terms of clay, total organic matter content and organic matter particle size fractions. The obtained data show that organic matter fractions differ according to particle size distribution and the prevailing soil management system. Stable organic matter content ( 100 μm) is strongly influenced by the type of soil management utilized.

THE IMPACT OF SINGLE TREES ON PROPERTIES OF LOESS‐DERIVED GRASSLAND SOILS IN ARGENTINA

The effect of single-tree influence areas on the physicochemical properties of the soil surface mineral horizon (0–18 cm) was studied in three stands of Pinus radiata D. Don introduced into Sierra de la Ventana, Argentina, grasslands 50 yr ago. Soil samples were taken at distances of 0, 1, and 2 m in transects from the tree to the periphery of the crown. Adjacent grassland soils with mollic epipedons were used as controls. Soil alteration was found to be highest near the trunk, with clear evidence of acid hydrolysis of primary silicates; the epipedon close to the trunk was classified as umbric rather than mollic. Decreasing values of pH, Ca, and exchangeable Mg, and increasing values of exchangeable H and Al, and also of fulvic acid-complexed Al, were registered from the grassland toward the axes of the trees. The soil properties analyzed fall into a distinctive spatial pattern of radial symmetry around each individual tree, with systematic and predictable variations, thus confirming the validity of the concept of “single-tree influence circles” for the study area. Each stand of P. radiata generates a patch of soil alteration within the undisturbed habitat matrix; the internal structure of these patches shows a radial pattern of different polypedons spatially and genetically associated with the inner ring of bark litter and the outer ring of leaf and twig litter. The present work shows that the introduction of P. radiata triggered changes in the evolutionary trend of the soils of such magnitude as to be reflected at the highest taxonomic level in soil taxonomy.

Soil degradation related to overgrazing in the semi-arid southern caldenal area of Argentina

The aim of the present study is to determine quantitatively the magnitude of the structural changes that occur in the soil during the degradation process affecting natural grassland in the semi-arid ecosystem of the southern area of the District of the Caldén, Argentina. Topsoil horizons show a reduction in depth from 20 cm in ungrazed sites to 16 cm in grazed sites, mainly as a consequence of soil compression caused by animal hooves. Bulk density values in the first 5 cm of the profile in grazed sites are approximately 27% higher than those in ungrazed sites. Total porosity values in the top few centimeters are, on average, 17% lower in grazed sites, primarily due to the collapse of macropores (>50 μm) and larger mesopores (50-9 μm). Water retention curves for the three depths in the different patches reflect the changes in pore space distribution. Grazing causes a sharp increase in mechanical impedance-an average increment of 210% over ungrazed values in the first 10 cm of soil. There are marked differences in the degree of aggregation in grazed sites compared with ungrazed sites. The former show a lower quantity and density of roots in the top few centimeters of the profile. Changes are also evident in average root diameter as a result of vegetation substitution brought on by overgrazing. The lack of significant differences in soil physical properties in areas subject to different grazing intensities underscores the gravity of the problem caused by animal traffic, which poses a serious threat to the conservation and recovery of the grazed patches.

Management discriminant properties in semiarid soils

The physical properties of coarse-textured soils in semiarid regions often deteriorate with use. We hypothesized that the changes in the physical properties of the soil were related to the cropping systems employed. Surface samples of 52 Entic Haplustolls under three different uses (24 under continuous cultivation (C), 18 under rotation with grass leys (R), and 10 virgin soils (V)) were analyzed for clay, silt, organic matter and water content, bulk density, compaction and aggregate stability. Data were analyzed statistically using principal components, canonical variables, and discriminant functions. A satisfactory segregation of the soils according to discriminant properties (coarse organic matter, aggregate stability, and susceptibility to compaction) was obtained. The model developed satisfactorily classified the soils under different uses (100% R, 83% C and 88% V). Principal component analysis also showed that bulk density, compaction, and wet aggregate stability are related to organic matter content. We conclude that, in the studied region, the lower the ratio of organic matter to clay + silt content, the more severe the physical deterioration of the soils.

Effect of clay minerals and organic matter on the cation exchange capacity of silt fractions.

The cation exchange capacity (CEC) and specific surface properties were investigated in four particle-size fractions < 50 μm from three loess (one Kastanozem and two Phaeozems), a holocene (Fluvisol) and a basalt soil (Nitisol) before and after destruction of organic matter. Particle-size fractions were separated by sedimentation after chemical and physical dispersion of the soil samples. Illite, amorphous minerals, mixed layers, smectite and kaolinite were the predominant clay minerals. They were detected in all size fractions. The CEC increased with increasing organic matter contents and this effect was more pronounced in coarser fractions. The organic matter content per unit surface area was two or three times larger in coarse silt than in clay, irrespective of the soil type.

A rapid method for estimating the carbon concentration of fulvic acids

Abstract A simple method was developed for estimating the carbon concentration of fulvic acid from soil extracts at pH 2. Visible absorbance (410 nm) was measured in 20 samples of fulvic acids from different regions of Argentina. Linear regression analysis of absorbance as a function of carbon concentration yielded a high correlation coefficient (r = 0.983∗∗). The proposed method is expected to be useful in assessing changes in organic matter content as a result of different tillage systems, erosion, plant residues, etc.

Provisional site quality evaluation for coniferous plantations in Sierra de la Ventana, Argentina

Provisional forest site classes were established for the most widely planted conifers in a temperate, hilly zone of Argentina. Growth data were obtained from 72 unmanaged stands. Aleppo pine (Pinus halepensis Mill.) was studied on 22 sites, Monterey pine (Pinus radiata D. Don.) on 20 sites, and deodar (Cedrus deodara (Roxb) Loudon) and Italian or common cypress (Cupressus sempervirens f. hprizontalis (Mill.) Voos) on 15 sites each. Site index, regarded as the height of dominants at the base age of 25 years, was determined by using stem analysis. Site indices as well as yields were higher for the species of genus Pinus, particularly for P. radiata followed by Cedrus deodara and Cupressus sempervirens, respectively. Data from stem analysis pointed out that the mean annual increments in the stands did not culminate even at the age of 30 years.

Comparative effects of sodium and potassium salts on the physicochemical conditions of soils

Abstract Though it is commonly held that sodium (Na) rather than potassium (K) salts affect soil properties, in some treatmets the opposite has been found to be the case. The present paper describes soil trials carried out to determine changes in organic matter and colloidal content, pH, cation exchange capacity, and exchangeable cations as a consequence of leachings with Na and K salts. It was possible to classify salts into weakly and strongly alkaline according to their effect on soil properties. On the basis of the effect of K on soil properties, it is concluded that this salts should be included in soil salinity classifications.

PHOSPHORUS CONTENT IN SOIL IN RELATION TO FULVIC ACID CARBON FRACTION

The fulvic acid fraction is considered an important constituent of soil organic matter and is sensitive to management regimes and tillage impact. Both humic acids (HA) and fulvic acids (FA) are able to form metal complexes which bind appreciable amounts of phosphate or phosphorus (P) species. The aim of the present study is to evaluate the fulvic acid carbon content of agricultural soils in Argentina and to explore the possible relationship between acid carbon (FC) content and the level of available P in the soil. A total of 74 surface samples of Hapludolls and Haplustolls covering areas with decreasing levels of annual rainfall were analyzed. It was found that soils with FC content >5.5 g kg−1 exhibited available P levels >30 mg kg−1, whereas available P levels <20 mg kg−1 were related to FC contents <4.0 g kg−1. Soils with high FC content thus currently have adequate P without supplementing it in the form of fertilizer. A more meaningful relationship is found between the FC fraction and available P than between P status and total organic carbon of soil.