Darwin W. Anderson

Direct measurement of organic carbon content in soils by the Leco CR‐12 carbon analyzer

Abstract A straightforward procedure is described for soil organic carbon (C) measurement in soil samples that may contain carbonates by using the Leco CR‐12 Carbon Analyzer. At a temperature of 840°C, a measured oxygen flow of 3.6 L min‐1, lancing flow of 1.0 L min‐1, soil organic C content can be directly measured on 0.20 to 0.40 g of samples, which have previously been ground to pass 40‐mesh sieve, for most medium‐ and fine‐textured soils. The organic C is combusted and measured within 2 min. A larger sample size of up to 2.5 g is suggested for sandy soils of low organic C content.

Landscape-scale changes in indicators of soil quality due to cultivation in Saskatchewan, Canada☆

Quantitative assessments of the impact of agricultural practises on soil quality have been hindered by the lack of basic spatial units for designing landscape-scale research projects. This paper builds on the relationship which has been demonstrated to exist between small (5 m by 5 m) slope segments and soil distribution in order to define larger landform element complexes in till landscapes of southern Saskatchewan, Canada. Distinctive pedogenic regimes are associated with these complexes. These complexes were then used to stratify the landscape at four conterminous sites with different cultivation histories and to assess changes in indicators of soil quality. Soil redistribution (as assessed by 137Cs redistribution) has had a major impact on these landscapes. The shoulder and level summit complexes have experienced continued high rates of soil loss. The shoulder complexes have lost 55% of their original soil organic carbon (a loss of 64 mg ha−1) over 80 years and 70% of this loss is attributable to net soil export from these positions. The portions of the footslope complexes dominated by Orthic Black Chernozemic soils initially act as sediment deposition sites in the first 22 years of cultivation, but ultimately this soil is removed from these positions and a moderate decline in soil quality occurs. The Gleysolic-dominated portions of the footslopes and the level depressional complexes occupy 15% of the landscape and are the major long-term sediment depositional sites; the biochemical indicators of soil quality (soil organic carbon and total soil nitrogen) show a major and beneficial increase in these positions.

Origin and rate of pedogenic carbonate accumulation in Saskatchewan soils, Canada

Abstract Limited information is available about inorganic carbon stocks in the boreal regions. The objective of this study was to determine the amount and accumulation rate of pedogenic carbonate (PC) in soils of the boreal grassland and forest regions of Saskatchewan, Canada. The storage of pedogenic carbonate increases from 134 kg m−2 in semiarid grassland (Brown soils) in the southwest to 165 kg m−2 in the northeast, under forest (Gray soils), within the time decreasing from 17,000 years in the southwest to 11,500 years in the northeast. The rate of pedogenic carbonate accumulation likewise increases from 8.3 to 14.3 g m−2 year−1 in the same direction. The results show that the soils of the prairies and forests have sequestered 1.4 times more C in the form of pedogenic carbonates than as organic matter. Stable carbon isotope values of pedogenic carbonate decreases from southwest to northeast. This is consistent with decreasing representation of C4 plants in the vegetation in the same direction. The rate of pedogenic carbonate accumulation increases with increasing annual precipitation. This suggests that the rate-limiting factor to precipitate with CO2 is Ca in the boreal region of Canada. Silicate weathering is more significant in Luvisols (Alfisols), suggesting that they may be most effective in truly sequestering additional amount of C in the soil.

Effects of cultivation and erosion on soils of four toposequences in the Canadian prairies

Abstract This study evaluates the effects of cultivation and topography on soil properties. Four toposequences (one uncultivated and three cultivated since 1910, 1930 and 1961) were sampled and their horizon depths, bulk densities, soil losses, organic carbon (C), total nitrogen (N), and total phosphorus (P) contents compared. Thin sola and A horizons with relatively high bulk densities and low amounts of organic matter, total N and total P at upper slope positions on cultivated fields indicated maximum erosional activity. Organic matter, total N and total P contents were increased in areas of deposition at lower landscape positions, whereas the thickness of the sola and A horizons increased and bulk density decreased. Substantial reductions in N, in excess of the amount removed by grain and straw, occurred with continuing cultivation. Lower slopes lost less N on a percent basis but absolute losses were greater than on upper slopes. Long term P fertilization maintained total P in the A Horizon of cultivated toposequences at levels similar to the thicker A horizon of the Native toposequence. Losses of P from non-eroded sites were comparatively less than losses of C or N. If the cultivated toposequence as a whole is considered, the largest C losses were due to mineralization in lower slope areas and were more than double the amounts lost by erosion at upper slope areas. In upper slope areas mineralization accounted for the largest portion of total C lost in the early years of cultivation, whereas erosion accounted for the largest portion in later years.

Organic carbon and sulphur compounds in wetland soils: insights on structure and transformation processes using K-edge XANES and NMR spectroscopy

Abstract X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectroscopy were used in combination to characterize organic carbon structures in a series of wetland soils in Saskatchewan, and XANES spectroscopy was also used to examine sulphur speciation in the soils. The organic C contents of most of the wetland soils are consistently higher by a factor of two to five times compared to adjacent well-drained soils. NMR analyses indicate that the organic matter in the wetland soils consists of predominantly aliphatic structures such as carbohydrates and long chain poly(methylene) units which are refractory structures found in plant waxes. The poly(methylene) structures have a significant capacity to sorb nonpolar organic molecules. The phenolic OH and carboxyl group content of the wetland soils studied is an additional significant factor in their sequestering ability for heavy metals or pesticides. Carbon XANES spectroscopy shows that the surface (∼10 nm) layer of particulate organic matter has a structure dominated by aromatic, carbohydrate and carboxylic acid-like material apparently derived from partially degraded lignin and cellulose polymers which are adsorbed onto clay minerals. The aliphatic structures remaining in this surface layer are probably recalcitrant (poly)methylene units. At a depth of ∼100 nm, the aliphatic content significantly increases suggesting the presence of more labile structures. The presence of these more labile aliphatic compounds may be due to slow decomposition rates in the wet, often cool environments present and to the protective action of the more refractory components in the surface ∼10 nm of the organic matter. Drying of the wetlands, either by draining or as a result of climate change, is likely to result in the rapid decomposition of these labile organic structures releasing carbon dioxide. Our data indicate that the preservation of the organic carbon compounds in these soils is a result of their presence as surface adsorbed layers on the soil mineral particles. The soils contain three different classes of sulphur compounds: reduced organic sulphur such as sulphides, low valent oxidized sulphur such as sulphoxides, and high valent oxidized sulphur such as sulphonate and sulphate. Of these, reduced sulphur species constitute between one-third and two-thirds of the total. Sulphonate structures comprise between a fifth and a third of the total. Sulphates exhibit a wide variation in content, and sulphoxides are either not detected or are present to a lesser extent (

Soil organic structures in macro and microaggregates of a cultivated Brown Chernozem

Abstract The chemical composition of soil organic binders and their role in aggregate stability is largely unknown. The purpose of this study was to characterize soil organic matter (SOM) in soil macro and microaggregates by pyrolysis field ionization mass spectrometry (Py-FIMS). In comparison with a wheat-fallow (WF) rotation, a continuous wheat (CW) system stored more organic C, maintained a greater proportion of water stable macroaggregates > 250 μm and was characterized by greater molecular diversity of SOM. The highest concentration of molecular ions in all aggregate fractions were carbohydrates, lignin monomers, N compounds, and alkylaromatics (each representing from 9 to 15% of total detected molecular ions). Lipids, lignin dimers and sterols were the least abundant (each representing from 0.3 to 4% of total detected molecular ions). Linear regression models showed that the proportion of water stable macroaggregates was correlated with the concentration of lignin dimers (r = 0.98), sterols (r = 0.94), alkylaromatics (r = 0.94) and lipids (r = 0.90). Chemical classes of organic compounds were not correlated with the proportion of water stable microaggregates.

Early stages of soil formation on glacial till mine spoils in a semi-arid climate

Abstract Strip-mining and the construction of spoil banks composed of unweathered, clay loam textured, moderately calcareous glacial till has provided a model system for studying soil formation in the semi-arid grasslands of southern Saskatchewan. Revegetation of fresh spoils probably occurred within a year or two and includes many native and introduced grasses and herbs. On spoil banks 28–40 years old soluble salts, particularly sodium salts, had leached to considerable depth. Greater soluble cation contents in the surface horizons, as compared to 2.5–5 or 5–10-cm layers, indicated a cycling of these nutrients by vegetation. Nitrogen has accumulated at a rate of 2.43 ± 0.12 g/m 2 /yr , organic carbon at a rate of 28.2 ± 4 g/m 2 /yr , suggesting that organic-matter levels characteristic of regional soils could be accumulated in 250–350 years. Cation-exchange capacities increased with the accumulation of organic matter. The fractional composition and spectral properties of humic acids indicated that the humus of soils 28 years old was similar to that of the normal, regional soils. Carbonate weathering appears to be quite slow in grassland environments.

Stable carbon isotopes of carbonate pendants from Chernozemic soils of Saskatchewan, Canada

Carbonate pendants are almost pure pedogenic carbonate that formed in an environment that may contain lithogenic carbonates. Pendants were sampled from three Chernozemic soils in Saskatchewan: a Calcareous Black soil of the Oxbow Association (C3 vegetation dominant), an Orthic Dark Brown profile of the Biggar Association, and a transect of four Dark Brown soils of the Amulet Association (both with mixed C3 and C4 vegetation). All the soils were developed from glacial deposits which contain 10 to 20% CaCO3. Pedogenic carbonate is composed of minute crystals in layered clusters about 0.5 to 4 μm in diameter. Lithogenic carbonate pebbles exhibit fine- and close-structured dolomite with large rhombohedral crystals. The δ13C values of the carbonate pendants in the Oxbow soil reflect the range of the δ13C values of the soil organic matter (−25.0 to −26.0‰), with a relatively consistent fractionation factor of +16.5‰. More positive δ13C values (−4.0 to −6.9‰) from the Biggar soil are consistent with the more positive δ13C value of the soil organic matter, as some of the organic matter is derived from blue grama, a C4 grass with a δ13C value of −16.0‰. More positive δ13C values for the Bk horizons of upper location in the Orthic Dark Brown soils suggest a higher proportion of C4 plants today than in the past.

Fine root mineralization, soil organic matter and exchangeable cation dynamics in slash and burn agriculture in the semi-arid northeast of Brazil

Abstract The objective of this study was to understand the causes of crop productivity decline on a soil cultivated by the slash and burn method. The contribution of ashes, fine roots, and soil organic matter (SOM) mineralization to the pool of available nutrients of a nutrient-poor Haplustox of the semi-arid zone of northeastern Brazil was documented. Ashes were the most important input of nutrients to the soil. The burning of the vegetation debris produced 11 Mg ha−1 of ash containing considerable quantities of Ca and K, and some N, Mg and P. The ashes, in general, contained more Ca and Mg, and less N and K, than the estimated requirements of the cassava (Manihot esculenta) crop during the cultivation cycle, whereas the P in ashes was equivalent to the crop P uptake. About 65% of the fine roots from the native vegetation decomposed in the soil during the first rainy season after the slash and burn, contributing Ca, N, and Mg to stores of available nutrients, with limited supply of K and P. The SOM content decreased with cultivation. The losses ranged from 4 to 16%, 6–18%, and 10–20%, for C, N and organic P, respectively. The sum of exchangeable cations, base saturation and pH increased after the burn, whereas the exchangeable Al and Al saturation strongly decreased, promoting better growing conditions for the cassava crop, particularly during the first years of the cultivation cycle. The soil properties reverted to pre-burn conditions within two or three crop years, productivity declined and the field was abandoned to natural fallow.

Cultivation effects on the nature of organic matter in soils and water extracts using CP/MAS 13C NMR spectroscopy

The objective of this study was to examine the chemical structure of the organic matter (SOM) of Oxisols soils in slash and burn agriculture, in relation to its biological properties and soil fertility. The CP/MAS 13C technique was used to identify the main structural groups in litter and fine roots as SOM precursors; to identify the changes on the nature of the SOM upon cultivation and the proportion of labile and stable components; and to identify the nature of the organics present in water extracts (DOC).Carbohydrates were the main structural components in litter whereas components such as carbonyl C, carboxyl C,O-alkyl C and alkyl C were more common in SOM. Phenolic C and the degree of aromaticity were similar in litter and SOM. Cultivation resulted in a small decrease in the relative proportion of carbohydrates in SOM, little change in the levels of O-alkyl C and carbonyl C, but an increase in carboxyl C, phenolic C and aromaticity of the SOM. The level of alkyl C in soil was higher than the level of O-alkyl C, indicating the importance of long-chain aliphatics along with lignins in the stabilization of the SOM in Oxisols. The SOM of Mollisols from the Canadian Prairies differed from the Oxisol, with a generally stronger expression of aromatic structures, particularly in a cultivated soil in relation to a native equivalent. Carbohydrate components were the predominant structures in the DOC, indicating their importance in nutrient cycling and vertical translocations in the Oxisol.