Soluble OC Research Articles

Pine Chip and Poultry Litter Derived Biochars Affect C and N Dynamics in Two Georgia, USA, Ultisols

Some biochars produced by pyrolysis of biomass have the potential to sequester C and enhance nutrient supplies in agricultural soils. A 28-day lab incubation was used to assess the potential effects of biochars derived from pine chips (PC) or poultry litter (PL) applied at five application rates (0, 22.5, 45.0, 67.5, and 90 Mg ha−1 equivalent). Biochars were applied to two acidic Ultisols, a Cecil sandy loam and a Tifton loamy sand, found in Georgia, USA. Cumulative basal soil respiration was measured over the 28-day incubation. Other soil properties measured before and after incubation were soil pH, total soil organic carbon (SOC), total soil N, soluble organic C (OC), soil mineral nitrogen (NH4+-N and NO3−-N), and microbial biomass C (MBC). Before incubation, addition of both PC and PL biochars increased soil pH, total SOC, and C:N ratio in both soils. Addition of the PL biochar increased total soil N, soluble OC, and NO3−-N in both soils, MBC in Tifton soil, and NH4+-N in Cecil soil. Addition of the PC biochar decreased NO3−-N in Cecil soil but increased it in Tifton soil. After the 28-day incubation, averaged across soils, pH increased in the 22.5 Mg ha−1 PC and 22.5 and 67.5 Mg ha−1 PL treatments, total SOC declined in the 45 and 67.5 Mg ha−1 PC treatments, and the C:N increased in soil controls and decreased in the 67.5 Mg ha−1 PC treatment. In Cecil soil, the MBC declined in PL treatments except at 90 Mg ha−1, and NH4+-N declined in the 90 Mg ha−1 PC treatments. In Tifton soil, MBC increased in the 45 Mg ha−1 PL treatment, and NH4+-N increased in all but the 22.5 Mg ha−1 PL treatments. Total N and NO3−-N did not change with incubation. Basal respiration was not affected by biochar, thought it was generally greater in Cecil than Tifton soil. Net SOC loss and the initial increase in soluble OC and MBC indicated potential C priming from adding both biochars. Increased NH4+-N with time in Tifton PL treatments indicated potential N priming. In Cecil soil, the PC biochar may have immobilized NH4+-N, but PL biochar likely supplied it. In Tifton soil, PC biochar appeared to be generally inert, but PL biochar supplied soluble OC and NH4+-N, although it might have inhibited nitrification.

Changes in Soil Biochemical Properties in a Cedar Plantation Invaded by Moso Bamboo

Moso bamboo (Phyllostachys edulis) is one of the widely growing bamboo species in Asia. Because of its fast growth and aggressive rhizomes, it is reported to invade other forests and reduce the biodiversity of forest ecosystems. To determine the changes in soil nutrient conditions due to moso bamboo invasion, this research measured the difference in soil labile carbon (C) and nitrogen (N) contents in a Japanese cedar (Cryptomeria japonica) forest invaded by moso bamboo in central Taiwan. The content of soluble organic C (SbOC), measured by both KCl and hot-water extraction methods, was lower in bamboo than cedar soils. This observation agreed with the finding that the more easily decomposed SbOC could be lost with bamboo invasion. In addition, both SbOCKCl and SbOCHW contents were positively correlated with microbial biomass C content, so the decreased labile organic C content in bamboo soils may reduce microbial biomass production. Principal component analysis revealed soil organic C content (total organic C, SbOC and acid-hydrolysable C) as the most important soil parameter affected by the bamboo invasion, followed by microbial biomass N and NO3− contents in soils. The soil quality index model also agreed with the degraded soil quality with bamboo invasion. In conclusion, the invasion of moso bamboo reduced the C and N pools in bamboo soil and degraded the overall soil quality.

Chemical diversity and incubation time affect non-additive responses of soil carbon and nitrogen cycling to litter mixtures from an alpine steppe soil

The mechanisms of litter-mixing effects on soil carbon (C) and nitrogen (N) cycling in alpine ecosystems remain inconclusive. In this study, we employed a four-month litter-mixing experiment to examine the relationship between litter chemical diversity, incubation time and litter-mixing effects on soil C and N fluxes from an alpine steppe ecosystem in Northern Tibet. Litter mixtures caused predominantly non-additive effects on soil C and N fluxes, with more synergistic effects for carbon dioxide (CO2)/nitrous oxide (N2O) emissions while more antagonistic effects for soluble organic C (SOC), total inorganic N (TIN), microbial biomass C (MBC) and urease activity (UA). Litter-mixture would largely increase the fluxes of CO2, N2O emission and SON, while decrease SOC, TIN, MBC and UA concentration. We calculated six chemical diversity indices, and found litter chemical diversity correlated with the strength of litter-mixing effect on soil C and N, but the indices we chose may be influenced our understanding of the relationship. Our results also showed that models including the chemical diversity indices and incubation time generally gave better explanation on variations of litter-mixing effects. This work demonstrated a general relationship between litter chemical diversity and non-additive responses of soil C and N cycling, and suggested that incubation time is an important factor in understanding the litter-mixing effects.

Structural characterization of charcoal size-fractions from a burnt Pinus pinea forest by FT-IR, Raman and surface-enhanced Raman spectroscopies

Charcoal is mainly composed by aromatic C but is characterized by several degrees of aromaticity, which complicate its identification and quantification in natural environments by conventional analyses. Charcoal is an almost ubiquitous component of soil, although often occurring in minor amounts. Hence, there is a great interest in studying the charcoal structure and understanding the behavior of charcoal in soils. In soil, it has been demonstrated that the chemical structure of charcoal is also dependant on its particle-size. In this paper we have applied infrared, normal Raman, SERS and SEF spectroscopies to study four size-fractions of charcoal (>2 mm, 2–1 mm, 1–0.5 mm and <0.5 mm) and their alkaline extracts from a burnt Pinus pinea forest. Second derivative FT-IR in agreement with the normal Raman spectroscopy have given information about the size of aromatic rings and the nature of substituted groups in size-fractions of charcoal. Carbon cluster size progressively decreased in the smallest fractions suggesting that higher graphitization and crystallization occurred in the coarsest fraction (>2 mm). The presence of organic N was well evidenced by the vibration of iso-cyanate and cyanamide groups in the fractions. This result is of great environmental importance because N may be immobilized in form of stable molecules like N-heterocyclic poliaromatic structures, and so persists in soils. The soluble organic C (SOC) extracted from charcoal size-fractions did not differ from the bulk charcoal in terms of IR and Raman spectra. Instead SERS and SEF provided further information regarding the ratio between the aromatic component and the aliphatic cross-linking one in studied fractions.

Stabilisation of HF soluble and HCl resistant organic matter in sloping tropical soils under slash and burn agriculture

Soil organic matter (SOM) stabilisation on tropical sloping land can be influenced by slash burning and erosion processes. However, information on the behaviour of potentially stable components of organic matter on burned sites is scarce. This study is focused on organic matter soluble after demineralisation of the samples with hydrofluoric acid (HF soluble) and organic matter remaining after hydrolysis with hydrochloric acid (HCl resistant), which are both part of the potentially stabile OM fraction in tropical soils. The objective was to examine their contribution to carbon stabilisation along a toposequence of soil profiles sampled in a small cultivated catchment in Northern Laos with slash burning as common agricultural practice. Bulk soil as well as residues after acid hydrolysis using HCl have been analysed for chemical composition and mean residence time of SOM. The tropical soils showed similar amounts of HF soluble and HCl resistant OC, representing between 20 and 60% of the total OC of the soils. OC stabilisation at the sites is chiefly determined by mineral interactions as shown by the good correlations of the clay and the HF soluble OC contents with 14C activity. Analysis of the chemical structure by solid state 13C nuclear magnetic resonance spectroscopy ( 13C CPMAS NMR) showed that aromatic carbon contributes substantially to HCl resistant organic matter. The 14C activity of the hydrolysis residue was lower compared to the untreated soil, reaching a 14C age of around 1000 years B.P. in B horizons. This is consistent with the observation that chemical recalcitrant black carbon, produced by slash burning, may remain on site for a long time, once it is incorporated into the mineral soil.

Soluble Organic Nitrogen Pools in Forest soils of Subtropical Australia

Soil soluble organic N (SON) plays an important role in N biogeochemical cycling. In this study, 22 surface forest soils (0–10 cm) were collected from southeast Queensland, Australia, to investigate the size of SON pools extracted by water and salt solutions. Approximately 5–45 mg SON kg−1, 2–42 mg SON kg−1 and 1–24 SON mg kg−1 were extracted by 2 M KCl, 0.5 M K2SO4 and water, on average, corresponding to about 21.1, 13.5 and 7.0 kg SON ha−1 at the 0–10 cm forest soils, respectively. These SON pools, on average, accounted for 39% (KCl extracts), 42% (K2SO4 extracts) and 43% (water extracts) of total soluble N (TSN), and 2.3% (KCl extracts), 1.3% (K2SO4 extracts) and 0.7% (water extracts) of soil total N, respectively. Large variation in SON pools observed across the sites in the present study may be attributed to a combination of factors including soil types, tree species, management practices and environmental conditions. Significant relationships were observed among the SON pools extracted by water, KCl and K2SO4 and microbial biomass N (MBN). In general, KCl and K2SO4 extracted more SON than water from the forest soils, while KCl extracted more SON than K2SO4. The SON and soluble organic C (SOC) in KCl, K2SO4 and water extracts were all positively related to soil organic C, total N and clay contents. This indicates that clay and soil organic matter play a key role in the retention of SON in soil.

Aporte de carbono solúvel pelo sistema radicular de arroz e sua influência nos teores de substâncias húmicas de um Latossolo Vermelho-Amarelo

O objetivo deste trabalho foi quantificar a contribuição da deposição de C-orgânico solúvel pelo sistema radicular de arroz e a evolução de CO2, durante 64 dias de incubação, em amostras de um Latossolo Vermelho-Amarelo com adição de glicose e de raízes de arroz coletadas em diversos estádios de crescimento da planta (aos 40, 60, 80, 100, 120 e 140 dias da semeadura). Foi realizado o fracionamento da matéria orgânica humificada para avaliar o efeito da adição de sistema radicular na composição do húmus do solo. A rizodeposição de C-orgânico via exsudatos e, ou, decomposição de tecidos mortos mostrou-se correlacionada com o estádio de desenvolvimento da cultura. A rizodeposição total foi estimada em valores ao redor de 90 g m-2 de C por ciclo da planta. A adição de C via raízes às amostras de solo promoveu intensa mineralização da matéria orgânica preexistente no solo, principalmente nos primeiros dias de incubação, e aumentou o teor de C na fração ácidos fúlvicos do húmus, no final do experimento.

Denitrification Potentials in Restored and Natural Bottomland Hardwood Wetlands

Wetland restoration projects are frequently evaluated by their hydrologic roles and vegetation characteristics, but their success in restoring biogeochemical processes, such as denitrification, is less well known. To determine how restoration of structure affects specific ecosystem processes, denitrification potential, soluble organic C (SOC) concentrations, and soil moisture were measured seasonally over a 1‐yr period in replicated natural bottomland hardwood (BLH) wetlands (NAT), restored BLH wetlands with hydrology reestablished (RWH), and restored BLH wetlands without hydrology reestablished (RWOH). Denitrification potential was significantly higher in NAT wetlands (657 ng N2O‐N g−1 soil h−1) than in RWOH (167 ng N2O‐N g−1 soil h−1) (P = 0.07). Soil moisture was highest in NAT wetlands and lowest in RWOH (P = 0.01), but no differences were measured in SOC concentrations in three out of the four seasons sampled. Because RWOH wetlands exhibited denitrification potentials which were significantly lower than NAT wetland sites, these results demonstrate that a BLH wetland restored without the natural hydrologic regime reestablished will not be a replacement for a natural BLH wetland in terms of biogeochemical processes such as denitrification.

Microbial nitrogen transformations in earthworm burrows

Earthworms play an active role in soil nitrogen cycling. Past research has shown that earthworm castings are enriched in NO 3 − and NH 4 + and show a high potential for microbial nitrification and denitrification. Little information is available on microbial populations and N transformations in the 1–2 mm thick soil lining of earthworm burrows (the drilosphere). We measured nitrifying bacterial populations, denitrifying bacterial populations, nitrification rates and denitrification rates of drilosphere and nondrilosphere soils. These measurements, in addition to measurements of NO 3 − concentration, NH 4 + concentration, soluble organic-C, pH and water content, were performed on drilosphere material from laboratory microcosms inoculated with Lumbricus terrestris L. and on drilosphere material collected from earthworm burrows in long term no-till plots. The drilosphere soil was enriched in NO 3 −, NH 4 + and soluble organic C and these soils had elevated populations of nitrifying and denitrifying bacteria relative to nondrilosphere soil. Drilosphere soil also had higher nitrification and denitrification rates. We postulate that earthworm-derived C and N deposited in the drilosphere facilitates the enrichment of N-transforming bacterial populations and that the elevated N-transformation rates results in an enrichment of NO 3 − in the earthworm burrow. This phenomenon has the potential for increased downward NO 3 − transport; however, the extent to which this potential is realized is not known.

Soluble Organic Carbon in a Biosolids‐Amended Mollisol

AbstractOrganic matter can be mobilized from many sources and transported in soil by precipitation, snowmelt, and water table fluctuations. Knowledge of the potential fluxes of soluble organic C in different kinds of soil is essential to improve global C budgets. We characterized the soluble and suspendable organic matter in a biosolids‐amended fine, smectitic, mesic Cumulic Vertic Endoaquoll under two vegetation treatments: switchgrass (Panicum virgatum L.) and cottonwood‐poplar hybrid (Populus × euramericana—clone NC‐5326). Soil organic C (OC) that was dispersed in 0.1 mM CaCl2 was fractionated according to molecular weight and polarity using dialysis membranes and XAD‐8 resin chromatography. Under both types of vegetation, addition of biosolids increased the amount of soluble OC (SOC) in the soil, particularly under switchgrass. Biosolids application shifted the molecular‐weight distribution of SOC to lower weights (&lt;14 000 Da). The concentrations of hydrophilic OC fractions exceeded those of hydrophobic OC in all treatments, although biosolids application increased the levels of both fractions. As the rate of biosolids addition increased, the 0 to 5 cm zone yielded smaller concentrations of extractable colloidal organic compounds than the 5 to 25 cm zone, and we attributed this to the high amounts of soluble salts introduced by biosolids application. A sequential extraction experiment showed that large amounts of colloidal organic compounds could be mobilized from the soil only after removal of the soluble salts. Our results suggest that biosolids amendments could increase the mobilization of hydrophilic, low‐molecular‐weight compounds in a soil while at the same time limiting the mobility of organic colloids.

Decreasing Metal Runoff from Poultry Litter with Aluminum Sulfate

AbstractAluminum sulfate [Al2(SO4)3·14H2O] applications to poultry litter can greatly reduce P concentrations in runoff from fields fertilized with poultry litter, as well as decrease NH3 volatilization. The objective of this study was to evaluate metal runoff from plots fertilized with varying rates of alum‐treated and untreated (normal) poultry litter. Alum‐treated (10% alum by weight) and untreated litter was broadcast applied to small plots in tall fescue (Festuca arundinacea Schreb.). Litter application rates were 0, 2.24, 4.49, 6.73, and 8.98 Mg ha−1 (0, 1, 2, 3, and 4 tons acre−1). Rainfall simulators were used to produce two runoff events, immediately after litter application and 7 d later. Both concentrations and loads of water‐soluble metals increased linearly with litter application rates, regardless of litter type. Alum treatment reduced concentrations of As, Cu, Fe, and Zn, relative to untreated litter, whereas it increased Ca and Mg. Copper concentrations in runoff water from untreated litter were extremely high (up to 1 mg Cu L−1), indicating a potential water quality problem. Soluble Al, K, and Na concentrations were not significantly affected by the type of litter. Reductions in trace metal runoff due to alum appeared to be related to the concentration of soluble organic C (SOC), as well as the affinity of SOC for trace metals. Metal runoff from alum‐treated litter is less likely to cause environmental problems than untreated litter, since threats to the aquatic environment by Ca and Mg are far less than those posed by As, Cu, and Zn.

Effect of Chemical Amendments on Ammonia Volatilization from Poultry Litter

AbstractAmmonia (NH3) volatilization from poultry litter results in a buildup of atmospheric NH3 in chicken houses, which is detrimental to both farm laborers and birds. Ammonia loss from litter is detrimental to the external environment because it results in acid rain, as well as low N/P ratios in litter, which increase the likelihood of excessive P runoff into adjacent water bodies. The objectives of this study were to determine the effect of various chemical amendments on NH3 volatilization and selected litter characteristics after 42 d. A laboratory study was conducted using the following amendments: Ca(OH)2 (calcium hydroxide), Al2(SO4)3·18H2O (alum), alum + CaCO3, FeSO4·7H2O (ferrous sulfate), and MLT (Multi‐purpose Litter Treatment, commercial product). Ammonia‐free air was continuously passed through air‐tight chambers containing amended litter and any NH3 volatilized from the litter was trapped in boric acid solutions, which were titrated daily for NH3 content. The study was carried out for 42 d. At this time, the litter was analyzed for pH, electrical conductivity (EC), soluble, organic C (SOC), metals, and soluble and total forms of N and P. The results of this study indicated that the addition of alum to poultry litter dramatically reduces NH3 volatilization (up to 99% less volatilization than controls). Decreases in volatilization resulted in higher total and soluble N in litter, which increased N/P ratios. Several of the compounds studied (particularly alum) were effective in decreasing water‐soluble P levels in litter. Therefore, we are proposing the use of alum as a litter amendment in poultry houses.

Molecular Weight Distribution of Soluble Organics from Laboratory‐Manipulated Surface Soils

AbstractTransfer of organic matter from solid to solution phase is the first step in the redistribution by leaching of organic C and associated elements in forest soil profiles. To examine the effects of disturbances on solubilization of organics, three A horizons and one O horizon were exposed to air drying, waterlogging, addition of urea, addition of ash, and addition of ash in combination with heating at 250 °C. Following incuhation at 20 to 22 °C for 1 to 50 d, soluble organic C (SOC) was extracted with 0.5 mM SrCl2. The SOC was 0.2 to 0.7% of total organic C in controls. Urea and heat‐plus‐ash treatments yielded up to 17 times more SOC than controls, and other treatments yielded up to three times more than controls. Distribution of SOC among molecular‐weight classes, as determined by dialysis, was 21 to 32% in the &lt;3500‐dalton class, 8 to 20% in the 3500 to 14 000‐dalton class, and 47 to 71% in the &gt;14 000‐dalton class. Urea treatment yielded a higher proportion of SOC in the &gt;14 000‐dalton class than in the controls, while air drying resulted in a lower proportion. Both the quantity and quality of soluble organics can be influenced by soil disturbances, but the specific response varies with the type of disturbance.

Nutrient Transformations in Sediments as Influenced by Oxygen Supply

AbstractThe oxidation status of sediments greatly affects biogeochemical processes. The objective of this study was to determine the influence of various levels of O2 on nutrient transformations in lake sediments. Decomposition of sediment organic matter was evaluated under varying levels of O2. Bulk sediment samples obtained from a hypereutrophic lake in central Florida were incubated in stirred microcosms at 25°C for 100 d at four O2 levels. The O2 levels were accomplished by bubbling N2 containing 0, 0.2, 2.0, and 20.0% O2 through the stirred suspensions. Redox potential (Eh) measurements indicated that the two highest O2 levels (i.e., 2.0 and 20.0% O2) resulted in oxidizing conditions (Eh &gt; 400 mV), whereas the lowest O2 levels (0 and 0.2% O2) resulted in reduced conditions (Eh &lt; −300 mV). First‐order rate constants calculated based on CO2 evolution were 0.00010, 0.00027, 0.00062, and 0.00068 d−1 for the 0, 0.20, 2.0, and 20.0% O2 levels, respectively. Methane was detected in the sediments incubated under 0 and 0.2% O2 level, with CO2/CH4 ratios of 3.5 and 160, respectively. Accumulation of soluble organic C (SOC) was greater under reduced conditions than oxidized conditions. Ammonium concentrations decreased rapidly in the oxidized treatments, with concurrent increases in NO3‐N concentrations, whereas under reducing conditions NH4‐N concentrations slowly increased. Rates of N mineralization were slightly higher under oxidized conditions. Although the ratio of N mineralized to CO2 evolved was higher at low O2 levels, the amount of N mineralized vs. the sum of C metabolites (CO2 + CH4 + SOC) was relatively constant under all O2 levels (6.7:1). Reducing conditions resulted in a depletion of SO2−4, whereas under oxidizing conditions SO2−4 concentrations increased, probably due to sulfide oxidation. Soluble reactive P concentrations were lower under oxidizing conditions.

Soil Microbial Biomass and Organic Component Alterations in a No‐Tillage Chronosequence

AbstractA no‐tillage (NT) chronosequence that had been continuously cropped to maize (Zea mays L.) for 0, 1, 2, 4, 7, 9, 15, or 20 yr on a Westmoreland silt loam (fine‐loamy, mixed, mesic Ultic Hapludalf) was examined for differences in microbial biomass, and soil organic C, N, P, and S. In the plowzone of the NT sites, biomass‐C, total C (TC), soluble organic C (SOC), total Kjeldahl N (TKN), organic P (OP), and organic S (OS) levels were generally greater in the soil surface (0 to 7.5 cm) layers than in the 7.5‐ to 15‐cm layers. In contrast, biomass‐C under conventional tillage (CT or 0‐yr NT site) in the soil surface layer was ∼50% of that in the 7.5‐ to 15‐cm layer, whereas levels of the organic components were nearly identical. Biomass‐C and organic component levels in the soil surface layers under NT were from 27 to 83% greater than those under CT. Opposite tillage method effects on these properties were usually found for deeper soil layers. Soil organic components, but not biomass‐C, were significantly (p ≤ 0.05) related to years under NT in the soil surface layer. Only biomass‐C was significantly (p ≤ 0.10) related to years under NT in deeper soil layers. When just “typical (i.e., nonmanured, moderate N‐rate)” sites were included in the regression models, only biomass‐C and SOC reservoir contents (total to 45 cm) varied significantly (p ≤ 0.10) with years under NT. Soil biomass‐C reached a maximum (786 kg·ha furrow‐slice−1) in the soil surface layer after only 1 yr under NT, approaching a level nearly equivalent to that under an improved pasture, then equilibrated in about 10 yr to a level approximately 30% greater than that under CT. These observations suggest that continual NT induces a predictable dynamic in soil biomass‐C, but not soil organic components, that is generally insensitive to a range of management differences. As a consequence, management practices designed to improve nutrient use‐efficiency, especially by controlling microbial mineralization/immobilization activity, should not only take into consideration tillage method but years under the tillage method as well.