Tracing N, K, Mg and Ca released from decomposing biomass to new tree growth. Part II: A model system simulating root decomposition on clearfell sites

The decomposing roots of harvested trees are a potential source of nutrients for new trees on both conventional and whole-tree harvested clearfell sites. Roots contain significant reservoirs of nutrients, but little is known about the magnitude and rate of their release. The aim of this study was to use stable isotope techniques in a model system to trace nutrients released by decomposing roots. Labelled biomass was obtained by growing Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings with a generous or poor nutrient supply containing elevated ¹⁵N, ⁴¹K, ²⁶Mg and ⁴⁴Ca. Labelled trees were re-potted in sand and in two contrasting soils types to remove them from the enriched isotope supply. After re-potting, the labelled above-ground biomass was harvested, removed and used in a separate study described previously (Part I of II). In the study described here (Part II of II), new Sitka spruce seedlings were planted alongside the labelled root systems. A full destructive harvest was undertaken after one growing season. Enriched ¹⁵N, ⁴¹K, ²⁶Mg, and ⁴⁴Ca were recovered in the new seedlings in both sand and soils. The elevated amounts of ¹⁵N, ⁴¹K, ²⁶Mg and ⁴⁴Ca recovered in new seedlings indicate that nutrients released from decomposing roots can make a direct contribution to the growth of new trees on restock sites. The success of this model system will provide guidance for the application of similar techniques in field experiments.     

Intensive culture of European black alder in central Indiana, U.S.A.: Biomass yield and potential returns to farmers

Growing interest in woody biomass for energy in the midwestern U.S. will require information on species and site productivities. We investigated 3, 6 and 14 year yields of the nitrogen-fixing tree species. European black alder, at three spacings on a marginally productive soil in central Indiana, U.S.A. The highest yield was 10 Mg ha⁻¹ yr⁻¹ at age three at the closest spacing of 0.5 × 1 m. Other spacings and ages provided smaller yields. Fertilization with phosphorus and potassium only provided a response in the initial 3 year rotation. Whole-tree and stem-only harvests removed varying levels of nutrients from the site. However, on these marginally productive sites where N and sometimes P are limiting, sustainable harvesting could be maintained due to the nitrogen-fixing capability of this species and the effects of N fixation on P availability. Preliminary economic analyses indicated that growing biomass on farms could be profitable, but only with farm or forestry program cost-sharing assistance. Where establishment expenses could be reduced by wider spacings, the use of seed rather than seedlings, or farmer-substituted labor, returns to the farmer were competitive with row-crop and timber production.     

Biomass and nutrient removal by willow clones in experimental bioenergy plantations in New York State

The development of short-rotation intensive cultural (SRIC) willow systems as a source of bioenergy and bioproducts is growing in the northeastern and midwestern United States. Important data for sustainable management such as nutrient removal and nutrient use efficiency in willow bioenergy plantations is lacking. This study reports wood biomass production, annual removal of nutrients, and nutrient use efficiency in experimental plantings of SRIC willow and poplar at Tully, New York. Effects of clone, fertilization, irrigation, planting density, and harvest cycle were analyzed.

Annual biomass production of 15–22 dryMg/ha removed 75–86, 10–11, 27–32, 52–79 and 4–5 kg/ha/year of N, P, K, Ca and Mg, respectively. For all the variables studied, the responses depended on clone. Fertilization and irrigation increased rates of nutrient removal by means of increased biomass production. Unlike planting density, harvest cycle significantly affected rates of nutrient removal and nutrient use efficiency. For clone SV1 (Salix dasyclados), an irrigated and fertilized planting with a density of 36,960 trees/ha harvested on a 3-year rotation had the highest biomass production and nutrient use efficiency, and the lowest rates of nutrient removal. The annual harvest cycle had the lowest nutrient use efficiency and the highest annual removal of nutrients suggesting that this choice would be most appropriate for biomass crops that are to be used as buffer strips to manage nutrient runoff from agricultural fields. An appropriate choice of clone, planting density, and harvest cycle could tailor the rates of nutrient removal and nutrient use efficiency to match the objective of the planting.     

Energy trade-offs between intensive biomass utilization, site productivity loss, and ameliorative treatments in loblolly pine plantations

Loblolly pine plantations are the most important source of forest products in the US and the slash remaining after conventional harvest represents a significant potential source of bioenergy. However, slash removal in intensive harvests might, under some circumstances, reduce site productivity by reducing soil organic matter and associated nutrients. Two complimentary studies in the Gulf Coastal Plain of the southeastern US were designed to test whether harvest intensity (level of biomass removal) could have a negative long-term impact on site productivity. Harvesting tree crowns in addition to the merchantable bole had a negative impact (18%) on pine biomass accumulation by age 7–10 years on 15 of 19 research blocks. Sites at risk of harvest-induced reductions in productivity were relatively unproductive prior to harvest and had low soil phosphorus (P) concentrations. Intensive harvesting, fertilization, and chemical control of non-crop vegetation were all energy efficient; the additional biomass energy gained through these practices was two-orders of magnitude greater than the energy needed to conduct the activities. Harvest of slash for bioenergy in the Gulf Coastal Plain of the southeastern US has the potential to reduce productivity on infertile soils, but fertilization has the potential to restore and even improve productivity on those sites in an energy-efficient way.     

Breakeven price of biomass from switchgrass,big bluestem,and Indiangrass in a dual-purpose production system in Tennessee

The objective was to determine the breakeven price for switchgrass (SG) (Panicum virgatum L.), a mix of big bluestem (Andropogon gerardii Vitman) and Indiangrass (BBIG) (Sorghastrum nutans L. Nash), and a combination of SG and BBIG (SG/BBIG) produced under three harvest treatments. Two-harvest treatments included a forage harvest at early boot (EB) and at early seedhead (ESH) plus a biomass harvest at fall dormancy (FD). The third harvest treatment was a single biomass harvest at FD. Mixed models were used to determine if there were differences in yield, crude protein, and nutrient removal for each of the native warm-season grass (NWSG) treatments at each harvest. The EB plus FD harvest system would be preferred over the ESH plus FD harvest system for all NWSG treatments. BBIG was the only NWSG treatment with a breakeven price for biomass that decreased with an EB harvest. For all three NWSG treatments, a producer would be better off harvesting once a year for biomass than twice for forage and biomass. The cost of harvesting and replacing the nutrients for the forage harvest was greater than the revenue received from selling the forage.     

Biomass system model estimates of short-rotation hardwood production in Hawaii

By coupling a short-rotation, intensive-culture (SRIC) biomass production model with a geographical information system and database, potential biomass supply (dry Mg) and delivered cost ($(dry Mg)⁻¹) of three promising tropical hardwoods, Eucalyptus grandis, E. saligna, and Leucaena leucocephala, were estimated at all locations identified as potentially available for tree plantations on the island of Maui. Analyses were performed at two scales-island-wide (10⁵ ha order of magnitude) for general land-use planning, and specific-site (10² ha order of magnitude) for field-level recommendations. The results are presented as yield and delivered cost maps and biomass supply curves for the entire island, and as management strategies depicted graphically as functions of growing space and rotation age that provide least-cost biomass feedstocks delivered from two specific field sites to a designated bioconversion facility on Maui. The methodology is a cost- and time-efficient means to provide useful information to land owners and other decision makers contemplating SRIC forestry as an alternative land use.     

Seasonal dynamics of nutrient accumulation and partitioning in the perennial C4-grasses Miscanthus × giganteus and Spartina cynosuroides

Seasonal variation in the accumulation and partitioning of nitrogen, phosphorus and potassium was determined in both the above-ground and below-ground dry matter of the potential energy crops Miscanthus × giganteus and Spartina cynosuroides. It is desirable from both economic and environmental perspectives that such crops should exhibit a high nutrient use efficiency and minimal nutrient losses to the environment. The N, P and K concentrations in the above-ground dry matter, at final harvest, were 5.0, 0.6 and 12.0 mg g⁻¹ respectively in M. × giganteus and 3.0, 0.4 and 1.0 mg g⁻¹ in S. cynosuroides. Both species exhibited the high N-use efficiency expected of C₄ plants. Nitrate leaching was negligible. At the end of the growing season, nutrients were translocated to the rhizomes and, in the case of M. × giganteus, recycled to the soil in shed leaves. Consequently the nutrient content of the crop offtake was low. It was calculated that the N, P and K requirements of a M. × giganteus crop producing an above-ground harvest of 1.5 kg m⁻² dry matter would be 9.2, 1.3 and 20.4 g m⁻² respectively. The corresponding nutrient requirements for S. cynosuroides would be 7.5, 1.7 and 8.8 g m⁻². Except for the K requirement of M. × giganteus, the N, P and K demands of both species were less than those of typical graminaceous crops, including maize.     

Growth,biomass and petroleum convertible hydrocarbons' yield of Grindelia camporum planted on an alluvial soil (Entisol) of North India and its response to sulphur fertilization

Four-week-old seedlings of Grindelia camporum Greene were planted in a mild calcareous alluvial soil collected from Mahibullapur, in Lucknow district (26° 30′ N latitude–80° 30′ E longitude) in pot culture. The soil, rated sulphur deficient on the basis of available soil sulphur, was fertilized with calcium sulphate to provide sulphur at the rate of 10, 25, 50, and 100 mg kg^?1 soil. Observations on growth (height, branching, leaf area) were recorded periodically. Plants were harvested 26 weeks after transplantation (wat) and measured for biomass and biocrude yields. After harvest, the pot soil was measured for available sulphur using three extractants: 0.15% CaCl₂, 0.5 M NaHCO₃, pH 8.5, and Morgan's extract.The native soil (control) is rated deficient in available sulphur; and availability of sulphur increased with increasing levels of sulphur fertilization. The vegetative growth of plants reached the maximum in response to sulphur amendment at the rate of 50 mg kg^?1 soil 14 weeks after transplantation to pots. At the time of harvest, 26 weeks after transplantation, plants showed best growth and maximum number of capitula and weight, in response to sulphur amendment at the rate of 100 mg kg^?1 soil. Thus, G. camporum showed a higher requirement of sulphur during the reproductive phase than for its vegetative growth and biomass yield. Maximum biocrude yield, both the total and ethyl acetate and methanol extractable fractions, was also obtained when sulphur was applied at the rate of 100 mg kg^?1 soil.     

Social availability of residual woody biomass from nonindustrial private woodland owners in Minnesota and Wisconsin

An important and potentially underused source of biomass that could be utilized in energy production is from nonindustrial private woodlands. We employ the Theory of Planned Behavior to estimate the social availability of woody biomass as a function of landowner behavior intent, landowner characteristics, forest land characteristics, and biomass price on stated willingness to harvest biomass in conjunction with a commercial timber harvest. A mail survey was administered to 1109 nonindustrial private woodland owners in a 26-county region in northeast Minnesota and northwest Wisconsin during the fall of 2009. Using binary logistic regression, we found payment level offered to harvest biomass plays a significant role in landowners' decisions, but that non-monetary factors are also important. Landowner attitudes and opinions regarding soil impacts, aesthetics, and energy independence were important predictors of stated willingness to harvest. Social norms as manifested through the influence of neighbors were also significant. These findings expand existing research and are useful for profiling nonindustrial private woodland owners to identify sustainable sources of biomass to supply a burgeoning bioenergy sector in the Lake States.     

Bio-oils from arid land plants: Flash pyrolysis of Euphorbia characias bagasse

The devolatilization of the bagasse obtained by solvent extraction of dried Euphorbia characias, a bushy plant growing in arid land of the Mediterranean area, was investigated under rapid heating conditions at atmospheric pressure using a bench-scale fluidized bed pyrolyser. Particle heating rates exceeded 10⁴°C s⁻¹. Bagasse was fed continuously at the rate of 6 g h⁻¹ directly into a sand bed fluidized by nitrogen operating in the temperature range of 400°–750°C. The yields of oils, gases and chars are reported. A maximum oil yield of 44% (wt/wt) (moisture free bagasse) was obtained at 500°C. Yields of gases, CO, CO₂, C₁–C₄ hydrocarbons increased with the rise in temperature, reaching a maximum at 750°C. Elemental analyses showed that the composition of oils and chars was dependent on pyrolysis temperature. The nitrogen content is fairly high; an upgrading process could be necessary for its remotion before the use of the bio-oil as combustible. The other characteristics of oils fall in the range of oils derived from other biomass feedstocks. Chars have a high HHV (15.36 MJ kg⁻¹ at 500°C), representing a valuable fuel.     

Biomass power cost and optimum plant size in western Canada

The power cost and optimum plant size for power plants using three biomass fuels in western Canada were determined. The three fuels are biomass from agricultural residues (grain straw), whole boreal forest, and forest harvest residues from existing lumber and pulp operations (limbs and tops). Forest harvest residues have the smallest economic size, 137 MW, and the highest power cost, $63.00 MWh⁻¹ (Year 2000 US$). The optimum size for agricultural residues is 450 MW (the largest single biomass unit judged feasible in this study), and the power cost is $50.30 MWh⁻¹. If a larger biomass boiler could be built, the optimum project size for straw would be 628 MW. Whole forest harvesting has an optimum size of 900 MW (two maximum sized units), and a power cost of $47.16 MWh⁻¹ without nutrient replacement. However, power cost versus size from whole forest is essentially flat from 450 MW ($47.76 MWh⁻¹) to 3150 MW ($48.86 MWh⁻¹), so the optimum size is better thought of as a wide range.

None of these projects are economic today, but could become so with a greenhouse gas credit. All biomass cases show some flatness in the profile of power cost vs. plant capacity. This occurs because the reduction in capital cost per unit capacity with increasing capacity is offset by increasing biomass transportation cost as the area from which biomass is drawn increases. This in turn means that smaller than optimum plants can be built with only a minor cost penalty. Both the yield of biomass per unit area and the location of the biomass have an impact on power cost and optimum size. Agricultural and forest harvest residues are transported over existing road networks, whereas the whole forest harvest requires new roads and has a location remote from existing transmission lines. Nutrient replacement in the whole forest case would make power from the forest comparable in cost to power from straw.     

Brash bale production on a clear-felled farm forest and comminution of bales to a biomass energy fuel

Utilising logging residues (termed brash in the UK) for energy production has become a focus for energy providers since the development of specialist baling machinery to improve the logistical and financial potential of this material. To explore a farm-scale operations scenario, brash from a mixed conifer, temperate zone forest was baled and chipped with commercial machinery to produce fuel-grade woodchip. Clear-fell logging procedures presented a range of brash configurations to facilitate baling machinery to produce compacted, tied, regular sized bales. Average hourly bale production and fresh weight tonnage output was 28 ± 2 bales/h and 12.4 t/h respectively. Extraction of bales and stacking along access road verges achieved an average 24 ± 2 bales/h. Woodchipping output averaged 11.8, 13.7 and 13.0 green t/h respectively for whole bale, log only and bale-log composite woodchip. Chipping production efficiency was affected by bale condition, handling and machinery performance but chiefly by site transport accessibility and logistical planning. The average total cost of in-farm delivered fuel quality woodchip product from brash bales was £25.22 (€29.67) per green tonne. Brash bale chips contained more than double the percentage of fines <6.3 mm compared to round log woodchips and also had significantly higher gross energy and nutrients content. Brash bale moisture content was observed to fluctuate widely and nutrients and energy content reduced during the 3-yr monitoring period. In conclusion, the combination of equipment and the confined production scenario was a viable process that provided fuel-grade woodchip at relatively low cost.     

Biomass and energy production in Casuarina equisetifolia plantation stands in the degraded dry tropics of the Vindhyan plateau, India

Two age groups of Casuarina equisetifolia (Forst.) plantation stands in the Renukoot forest division of the Vindhyan plateau were investigated over the span of three years for total and component biomass, annual net primary production, energy storage and annual net energy fixation. A high range of biomass (44–81 t ha⁻¹) was recorded in a densely populated stand at ages 5–7 years in comparison to a sparsely populated stand at ages 8–10 years. The contribution of the hole component gradually increased with increasing diameter class while foliage and branch components had a large proportion of biomass in the lower diameter classes. Maximum litterfall occurred in May and foliage litter contributed 87–95% of total litterfall. The energy content and storage in component parts were higher than some other promising tree species for energy plantation in the dry tropics. Production estimates of 19–29 t ha⁻¹ yr⁻¹ showed that the performance of Casuarina is good for dry tropical conditions. The biomass accumulation ratio and production efficiency showed a significant positive and negative (logarithmic) relationship, respectively with plantation age. The energy conserving efficiency of the 5-year old stand was more than twice that of the 8-year old stand.     

Harvest schedule to fill storage for year-round delivery of grasses to biorefinery

Number of annual harvest days is a critical variable in the scheduling of year-round delivery of grasses to a biorefinery. It defines the number of harvest machines required and the size of satellite storage capacity. An increase in both these parameters increases capital cost and thus the average delivered cost of biomass for year-round operation. The objective of this study was to determine the impact (number of harvest machines required and storage capacity required) of several harvest scenarios for switchgrass (Panicum virgatum). Calculations were done for a database of potential production fields within a 48-km radius of Gretna, Virginia. Four harvest scenarios were chosen ranging from short, October–December to extended, July–March. The extended harvest required only 33 round balers while the short (October–December) harvest required 64; consequently, capital cost for extended-harvest balers was only 51% of the baler capital cost for the short season. Maximum required storage capacity was 75% of the total annual harvest for the short season and 44% for the extended season. Capital cost to build storage was reduced by 41% by selecting the extended harvest season.     

Agronomic characteristics of US 72-1153 energycane for biomass

Biomass production and plant quality vary between plant species and morphological components of a plant. The purpose of this two-part experiment was (1) to study the influence of energycane [Saccharum sp. (L.) ‘US 72-1153’] harvest treatments (6) on dry biomass yield and (2) monitor changes in quantity and quality of plant components with increased plant height. Treatments for Part 1 determined the influence of plant height when harvested at 1.2, 2.5, and 3.7 m, mature stage in October (4.9 m, in flower), mature stage in December (4.9 m, in flower), and additional treatment harvested in October, which received half the total N (168 kg ha⁻¹) on dry biomass yield from 1986 to 1989. Part 2 treatments were to monitor changes in quantity and quality (crude protein and in vitro organic matter digestion) of plant components (green leaf, dead leaf, and stem) at 0.6 m plant height increments to a final height of 4.3 m during 1986 and 1987. Treatments from both parts of the study received 25 kg P ha⁻¹ and 93 kg K ha⁻¹ in one application and 336 kg N ha⁻¹ yr⁻¹ in single or split applications applied prior to growth of each harvest. Plants repeatedly harvested at the 1.2 m height (Part 1) and mature stage produced a 4-year average yield of 10 and 48 Mg ha⁻¹ yr⁻¹ dry biomass, respectively and decreased in dry biomass yield 89% (1.2 m harvest) and 53% (mature harvest) between years 1 and 4. The stem (1986 and 1987) and dead leaf (1986) plant components increased quadratically as plant height increased, and green leaf decreased from 70% (0.6 m) to 17% (4.3 m height). The crude protein concentration decreased 51% (green leaf) and 81% (stem) and in-vitro organic matter digestion decreased 54, 32, and 34% for dead leaf, green leaf, and stem, respectively as plant height increased from 0.6 to 4.3 m. These data indicate that harvest management is an important factor for energycane biomass yield, ratoon-crop success and plant quality if biomass is used as a methane source.     

生物质气化工艺废水特征及预处理实验研究

对生物质气化中试现场产生的废水进行了水质及水量特征分析,针对生物质气化工艺废水固体颗粒含量高、有机物浓度高、难生化降解、废水增量少的特点,采取减压蒸馏及芬顿氧化对生物质气化废水进行预处理。实验结果表明,在85 ~ 90℃、真空度 -0.07 ~ -0.095 MPa减压蒸馏条件下,废水COD、NH₄-N脱除率分别为74.38%、94.46%;在Fe²⁺-H₂O₂体系中,考察了H₂O₂与废水质量比、H₂O₂与Fe²⁺摩尔比、反应时间、H₂O₂浓度对COD、NH₄-N、TOC、TN等的影响,当H₂O₂与废水质量比为8.40%时,可将减压蒸馏蒸出液COD从2.05 × 10⁴ mg/L降至4.11 × 10³ mg/L,NH₄⁺-N从143 mg/L降至11.1 mg/L。     

Nutrients and energy in proleptic branches and leaves of poplar under a short-rotation coppice

Renewable energy is often generated from biomass, produced in short-rotation coppice (SRC) cultures. These cultures are frequently established on former agricultural land with ample availability of plant nutrients as nitrogen, phosphorous, potassium, calcium and magnesium. Nevertheless, little is known about the annual recycling of these nutrients through the leaves, as well as about the amounts that are removed at harvest. We therefore quantified soil nutrient concentrations, as well as nutrient concentrations and the gross calorific value of the proleptic branches and of the leaves of 12 poplar (Populus) genotypes in the second rotation of an operational SRC (with two-year rotations). For the produced leaf biomass, we also quantified the standing energy stock and the nutrient stock of each genotype. After four years the P, K, Ca and Mg soil concentrations had not significantly changed, while the N concentration at 30–60 cm of soil depth had significantly increased. On average, the standing aboveground woody biomass of the 12 genotypes in 2013 was 13.75 Mg ha⁻¹ and the total leaf biomass was 3.54 Mg ha⁻¹. This resulted in an average standing energy stock in the leaves of 64.8 GJ ha⁻¹. Nutrient concentrations were lower in the proleptic branches as compared to the leaves, but the proleptic branches and leaf nutrient concentrations significantly varied among the genotypes.     

Conversion of straw and similar agricultural wastes

Mainly the economic aspects prevent a far more extensive use of biomass, including straw as a fuel in energy supply.

During the latest years several straw fired plants have been put in operation, especially in Denmark, and they have demonstrated that both district heating and combined heat and power (CHP) production based on straw are technically possible.

However, experience has shown that a very precise research and development effort is necessary before the straw fired plants are competitive to traditional plants fired with fossil fuels, as to operational safety and economy.

The R & D activities ought first and foremost to aim at: 1) Reduction of costs connected to all processes from harvest to energy production, 2) wider know-how of the firing and combustion technical characteristics of straw, and 3) environmental conditions, including emissions and ash depositing problems.     

Variability and plasticity of productivity,water-use efficiency,and nitrogen exportation rate in Salix short rotation coppice

Short rotation coppice (SRC) willow plantations may play an important role in the future for biomass production purposes. However, the high planting density schemes combined with the frequent harvests occurring in such plantations could rapidly deplete soil resources. The use of genotypes able to produce greater amounts of biomass by using the least water and nutrients may help mitigating this risk. This study aimed at assessing among six willow genotypes (1) the variability of traits related to productivity (e.g. aboveground dry biomass or stem height), leaf and wood nitrogen (N) contents, N exportation rate and water-use efficiency (WUE) as estimated through bulk leaf carbon isotope discrimination (Δ¹³C), (2) the relationships among traits, and (3) the plasticity of these traits and of the relationships among them across different sites. The six genotypes were grown under SRC at three sites in northern France differing primarily in pedoclimatic characteristics for two years. A significant genotypic variability was found for all traits, except for the N exportation rate. The pedoclimatic context impacted the values of all traits, and the genotypic ranking for traits related to productivity and for Δ¹³C. Δ¹³C was negatively correlated with total shoot dry biomass and/or height irrespective of the site, meaning that the most productive genotypes were also the most efficient to use water. In conclusion, no antagonism was detected between biomass production and WUE. The most productive and most water-use efficient genotypes were the ones responsible for the highest nitrogen removal from the plantation during harvest.     

Carbon dynamics subsequent to establishment of switchgrass

It is necessary to develop new, clean and renewable biofuels to mitigate the greenhouse effect and reduce dependence on nonrenewable fossil fuels. Switchgrass (Panicum virgatum L.) has been chosen by the US Department of Energy as its model herbaceous energy crop in the Southeast due to high yields, low production costs, economic benefits, and little competition from existing enterprises. However, knowledge of its influence on soil carbon (C) dynamics is limited, as no systematic study of soil C dynamics in switchgrass culture has been conducted. Our objective was to determine C dynamics subsequent to switchgrass establishment and the impact of cultural practices (row spacing and harvest frequency) on C biogeochemical characteristics in a sandy loam soil (Typic Paleudult) and a clay loam soil (Typic Hapludult). Results indicated that soil C characteristics changed over time after switchgrass establishment. Carbon mineralization, microbial biomass C, C turnover, and % microbial biomass C in organic C was generally higher approximately 2 years after switchgrass planting than after its initial establishment in a sandy loam soil. Specifically, C mineralization increased by 112 and 254% at depths of 0–15 cm and 15-30 cm, respectively; microbial biomass C increased by 168% in the top 15 cm of soil; and C turnover increased by 116 and 255% at 0-15 cm and 15–30 cm, respectively. Microbial biomass comprised 0.76±0.09% and 0.75±0.19% of soil organic C in 0–15 cm and 15–30 cm depths, respectively, of sandy loam soil, while it made up 1.37±0.22% and 1.11±0.19% of soil organic C in the same soil depths in clay loam soil. Harvesting once resulted in more C turnover than harvesting twice in the sandy loam soil. Linear regression between soil C characteristics and switchgrass root weight, root C, and root nitrogen (N) returned to soil support the conclusion that soil C accumulation is positively related to root input. It appears that switchgrass establishment may have dual benefits as a source of renewable energy and as a means of improving soil quality. However, longer periods of study will be required to elucidate substantial gains in soil quality owing to switchgrass culture.