Effects of Cutting Phenology (Non-dormant Versus Dormant) on Early Growth Performance of Three Willow Clones Grown Under Different Weed Treatments and Planting Dates

To assess the effects of cutting phenology on early growth performance of three willow clones grown under different weed treatments and planting dates, freshly harvested (non-dormant) and cold-stored (dormant) cuttings from willow clone Tora, Jorr, and Olof were planted in bucket experiment outdoors in central Sweden on five planting dates (May–June 2013) with or without a model weed (spring barley). Non-dormant cuttings sprouted faster than dormant cuttings when planted early in the season. For cuttings planted later in the season, bud sprouting was affected only by willow clone. Aboveground biomass production was affected by cutting phenology, planting date, clone, and weed treatment. When planted on May 3 and May 10, biomass produced from non-dormant and dormant cuttings did not differ, while willows grown from dormant cuttings produced 59% more aboveground biomass than willows grown from non-dormant cuttings when planted on May 24–June 16. Tora produced on average 12% more biomass than Jorr and Olof, and weed competition reduced aboveground biomass production on average with 36%. The ability of willow to suppress weeds (WSA) was 26 (non-dormant cuttings) and 12% (dormant cuttings) higher for willows planted on May 3 compared with WSA of willows grown from cuttings planted later in the season. The ability to tolerate competition from weeds (WT) was 51 and 52% lower for willows grown from non-dormant and dormant cuttings planted late in the season compared with WT of willows planted earlier in the season. We conclude that planting with long-term cold storage of willow cuttings can be replaced with planting freshly harvested cuttings when planting is performed in early season, and that weed competition strongly reduces biomass production. Weed control during the establishment phase is crucial in order to maximize willow biomass production.     

Establishment and Early Growth of Willow at Different Levels of Weed Competition and Nitrogen Fertilization

To evaluate the effects of weed competition and nitrogen fertilization on the early growth performance of willow, cuttings of the clone Tora (Salix schwerinii x S. viminalis) were planted in buckets together with model weeds (spring barley or white mustard) sown 15, 26, and 30 days after willow planting. The buckets were fertilized with 30 or 90 kg N ha^?1. Willow with weeds sown after 15 days produced less biomass and smaller leaf area and had a lower maximum shoot height compared to willow planted without weeds and willow with weeds sown after 26 or 30 days. Fertilization with 90 kg N ha^?1 gave higher willow biomass production in willow with weeds sown after 26 or 30 days. Type of model weed had no effect on willow performance. Weed biomass and maximum shoot height were higher in weeds planted without willows compared to the willow-weed mixtures. A high nitrogen level gave more weed biomass when planted without willows and in the willow-weed mixture with weeds sown after 15 days. We conclude that for the given high density of willow, competition from weeds emerging soon after willow planting had strong effect on early production. Furthermore, if there is a risk of weed infestation, fertilization should be delayed.     

Field Evaluation of Willow Under Short Rotation Coppice for Phytomanagement of Metal-Polluted Agricultural Soils

Short rotation coppice (SRC) of willow and poplar might be a promising phytoremediation option since it uses fast growing, high biomass producing tree species with often a sufficient metal uptake. This study evaluates growth, metal uptake and extraction potentials of eight willow clones (Belders, Belgisch Rood, Christina, Inger, Jorr, Loden, Tora and Zwarte Driebast) on a metal-contaminated agricultural soil, with total cadmium (Cd) and zinc (Zn) concentrations of 6.5 ± 0.8 and 377 ± 69 mg kg^?1 soil, respectively. Although, during the first cycle, on average generally low productivity levels (3.7 ton DM (dry matter) ha^?1 y^?1) were obtained on this sandy soil, certain clones exhibited quite acceptable productivity levels (e.g. Zwarte Driebast 12.5 ton DM ha^?1 y^?1). Even at low biomass productivity levels, SRC of willow showed promising removal potentials of 72 g Cd and 2.0 kg Zn ha^?1 y^?1, which is much higher than e.g. energy maize or rapeseed grown on the same soil. Cd and Zn removal can be increased by 40% if leaves are harvested as well. Nevertheless, nowadays the wood price remains the most critical factor in order to implement SRC as an acceptable, economically feasible alternative crop on metal-contaminated agricultural soils.     

Genotype identity has a more important influence than genotype diversity on shoot biomass productivity in willow short‐rotation coppices

Willow (Salix spp.) short‐rotation coppice is commercially grown to produce lignocellulosic biomass to meet renewable bioenergy demands. Most commercial willow coppices are grown in stands of a single genotype, but biomass productivity may be greater in mixed communities, and the productivity in mixed communities may depend on the specific genotypes involved. We assessed the biomass production of four different Salix genotypes (“Björn,” “Jorr,” “Loden,” “Tora”) grown without additional nutrient fertilization during one cutting cycle at three locations in Europe (Uppsala in Sweden, Rostock and Freiburg in Germany) in plots of pure and mixed communities. We evaluated (i) the effect of genotype diversity on shoot biomass productivity, including the evidence for complementarity and selection effects; (ii) the influence of individual genotypes on mixed community productivity; and (iii) the productivity of individual genotypes in response to pure vs. mixed culture. Mean shoot biomass production after the first cutting cycle decreased in the order Rostock (8.7 Mg ha^?1) > Freiburg (6.9 Mg ha^?1) > Uppsala (5.7 Mg ha^?1), with values similar to those for other nonfertilized willow stands after the first growth cycle. Consistently across all three locations, increasing genotype diversity did not significantly affect shoot biomass production. Using Bayesian statistics, the addition of the genotypes “Jorr” and “Loden” was predicted to enhance shoot biomass production, while “Tora” and “Björn” are more likely to reduce shoot biomass production in mixed communities. In addition, we found evidence for a negative selection effect due to the genotype “Tora” performing better in mixed than in pure communities in two of the sites (Freiburg, Uppsala). In conclusion, our results imply that increasing genetic richness has no negative effect on productivity and that there is a potential to design site‐specific genotype mixtures of short‐rotation coppice promoting both high genetic diversity and high biomass production.     

Impact of Nitrogen Fertilization to Short-Rotation Willow Coppice Plantations Grown in Sweden on Yield and Economy

A fertilization trial was carried out in established short-rotation willow coppice (SRWC) plantations of two bred varieties of willow (Salix spp.; "Tora" and "Jorr") at five sites in central Sweden between 2008 and 2010. Mineral nitrogen was applied at four different rates: No fertilization (Control), 160 kg nitrogen ha^?1 as a single dose after harvest (Economy), 60–100–60 kg nitrogen ha^?1 in year 1–2–3 (Normal), and 160 kg nitrogen ha^?1 year^?1 in years 1–3 (Intensive), using a randomized block design with four replicates. The yield response (biomass increase per kg fertilizer nitrogen) was 65, 67 and 46 kg kg^?1 in the Economy, Normal and Intensive treatments, respectively. The results from the fertilization trial were used for economic calculations of different fertilization strategies given varying costs for fertilization and marginal value of the increased yield (price received for wood chips minus the costs for harvest and transportation of wood chips to a district heating plant). Comparative calculations were made based on data from a previous fertilization trial during the first cutting cycle of old, non-bred varieties. The calculations showed positive net present values of fertilizing bred willow varieties given a realistic fertilization response and a price for wood chips close to the market price for forestry-based wood chips in Sweden.     

Growth Response of Coyote Willow (Salix exigua) Cuttings in Relation to Alluvial Soil Texture and Water Availability

A common approach to re‐establishing cottonwood–willow habitat along regulated rivers is through installing dormant, rootless cuttings, yet there is little published information exploring floodplain characteristics that optimize growth of southwestern riparian willows planted in this manner. The goal of this project was to evaluate relationships between growth attributes of Salix exigua and soil texture and soil water availability. Monitoring plots were established in five willow swales planted with dormant S. exigua cuttings along the banks of the Middle Rio Grande in central New Mexico. Data analysis revealed significantly higher aerial cover, height, and stem density for S. exigua plants installed in plots with intermediate levels (15–25%) of fine textured soils distributed through the soil profile. Similar relationships were found in relation to soil water availability. Regression analysis of percent fines and available water at different depth increments provided limited explanation of variability in willow growth attributes at different plots. Findings indicate that S. exigua plants established from cuttings can achieve heights and aerial cover values similar to naturally established willow bars if the floodplain soil profile contains intermediate levels of fine textured soils and the maximum depth to groundwater is within 1.5 m of the ground surface. Where sites are dominated by coarse sand, S. exigua growth may be improved if maximum depth to groundwater is within 1 m of the ground surface.     

Carbon Sequestration in Fine Roots and Foliage Biomass Offsets Soil CO2 Effluxes along a 19-year Chronosequence of Shrub Willow (Salix x dasyclados) Biomass Crops

Previous greenhouse gas (GHG) assessments for the shrub willow biomass crops (SWBC) production system lacked quantitative data on the soil CO₂ efflux (F_c). This study quantifies the mean annual cumulative F_c, the C sequestration in the above- and belowground biomass, and the carbon balance of the production system. We utilized four SWBC fields, which have been in production for 5, 12, 14, and 19 years. Two treatments were applied: continuous production (CP)—shrub willows were harvested, and stools were allowed to regrow, and tear-out (TO) (crop removal)—shrub willows were harvested, and stools were sprayed with herbicide following spring, crushed, and mixed into the soil. Mean annual cumulative F_c were measured using dynamic closed chambers (LI-8100A and LI-8150). Across different age classes, the mean cumulative F_c ranged from 27.2 to 35.5 Mg CO₂ ha^?1 year^?1 for CP and 26.5 to 29.3 Mg CO₂ ha^?1 year^?1 for TO. The combined carbon (C) sequestration of the standing above- and belowground biomass, excluding stems, ranged from 50.6 to 94.8 Mg CO₂ eqv. ha^?1. In the CP treatment, the annual C sequestration in the fine roots and foliage offsets the annual cumulative F_c. Across different age classes, C balances ranged from ?21.5 to ?59.3 Mg CO₂ ha^?1 for CP and 26.5 to 29.3 Mg CO₂ ha^?1 for TO. The GHG potential of SWBC is about ?36.3 Mg CO₂ eqv. ha^?1 at the end of 19 years, suggesting that the SWBC system sequesters C until termination of the crop.     

Willow production during 12 consecutive years—The effects of harvest rotation,planting density and cultivar on biomass yield

Willow biomass produced in short rotation coppice systems can potentially be used as biomass feedstock in Europe, the United States and Canada. However, most researchers focus on data from the first harvest rotation only, whereas multiple rotations have been rarely investigated. The aim of this study was to evaluate the effect of cultivar (5), planting density (12,000–96,000 cuttings/ha) and harvest rotation (annual, biennial, triennial) on willow biomass yields during 12 consecutive years in northern Poland. Every experimental factor and the interactions between factors significantly impacted willow yields. Biomass yield was highest in the triennial harvest rotation (13.3 Mg ha^?1 year^?1), 15.9% lower in the biennial rotation and 26.9% lower in the annual rotation. The highest average yield (14.6 Mg ha^?1 year^?1) was noted at a planting density of 24,000 cuttings/ha, and yields were 9.3%–46.0% lower at the remaining densities. Cultivar UWM 095 had the highest average yield (13.0 Mg ha^?1 year^?1), whereas the yield of the remaining cultivars was 4.6%–32.4% lower. During the 12‐year period, yields were higher after the first harvest in annual, biennial and triennial harvest rotations. This above implies that high biomass yields can be obtained after the first harvest rotation if willows are cultivated on fertile soils at higher planting density, well managed and coppiced after the first year. However, yields are unlikely to be higher in successive harvest rotations, and they can even be lower, but more stable than in the first harvest rotation.     

Phytoremediation of groundwater contaminated with pesticides using short-rotation willow crops: A case study of an apple orchard

The occurrence of pesticides in groundwater represents an important health issue, notably for population whose drinking water supply source is located in agricultural areas. However, few solutions have been considered with regard to this issue. We tested the efficacy of a vegetal filtering system made of shrub willows planted at a high density (16,000 plants ha^?1) to filter or degrade pesticides found in the groundwater flowing out of an apple orchard. Ethylene urea (EU), ethylene thiourea (ETU), tetrahydrophthalimide (THPI), atrazine, and desethylatrazine were monitored in the soil solution in willow and control plots over one growing season. ETU and atrazine concentrations were lower in the willow plots relative to the control plots, whereas desethylatrazine concentration was higher in the willow plots. No significant difference was detected for EU and THPI. Furthermore, pesticide concentrations displayed complex temporal patterns. These results suggest that willow filter systems can filter or degrade pesticides, notably ETU and atrazine, and could be used for phytoremediation purposes. Yet, this potential remains to be quantified with further studies using experimental settings allowing more estimation in time and space.     

In-situ phytoextraction of Ni by a native population of Alyssum murale on an ultramafic site (Albania)

Ultramafic outcrops are widespread in Albania and host several Ni hyperaccumulators (e.g., Alyssum murale Waldst. &; Kit.). A field experiment was conducted in Pojske (Eastern Albania), a large ultramafic area in which native A. murale was cultivated. The experiment consisted in testing the phytoextraction potential of already installed natural vegetation (including A. murale) on crop fields with or without suitable fertilisation. The area was divided into six 36-m² plots, three of which were fertilised in April 2005 with (NPK + S). The soil (Magnesic Hypereutric Vertisol) was fully described as well as the mineralogy of horizons and the localisation of Ni bearing phases (TEM-EDX and XRD). Ni availability was also characterised by Isotopic Exchange Kinetics (IEK). The flora was fully described on both fertilised and unfertilised plots and the plant composition (major and trace elements) and biomass (shoots) harvested individually were recorded. The soil had mainly two Ni-bearing phases: high-Mg smectite (1.3% Ni) and serpentine (0.7% Ni), the first one being the source of available Ni. Ni availability was extremely high according to IEK and confirmed by Ni contents in Trifolium nigriscens Viv. reaching 1,442 mg kg^?1 (A new hyperaccumulator?). Total biomass yields were 6.3 t ha^?1 in fertilised plots and 3.2 t ha^?1 in unfertilised plots with a highly significant effect: fertilisation increased dramatically the proportion of A. murale in the plots (2.6 t ha^?1 vs. 0.2 t ha^?1). Ni content in the shoots of A. murale reached 9,129 mg kg^?1 but metal concentration was not significantly affected by fertilisation. Phytoextracted Ni in total harvest reached 25 kg Ni ha^?1 on the fertilised plots. It was significantly lower in unfertilised plots (3 kg Ni ha^?1). Extensive phytomining on such sites could be promising in the Albanian context by domesticating already installed natural populations with fertilisation.     

Profitability of Willow Biomass Crops Affected by Incentive Programs

The economics of willow biomass crops are strongly influenced by yield, production, and harvesting costs and the delivered price for biomass. Under current management practices, willow biomass crops with yields of 12 oven-dried metric tons (odt)?ha^?1 year^?1 and a delivered price of $60 odt^?1 have an internal rate of return (IRR) of about 5.5 %. Yields below 9 odt ha^?1 year^?1 have an IRR <0 %. We examined the impact of different incentive programs on the returns from willow biomass crops and the hectares or tons of willow biomass supported across a range of yields. Incentive programs examined included establishment grants (EG), annual payments (AIP), low cost startup loans, and matching payments offered by two existing programs, the Conservation Resource Program (CRP) and more recently the Biomass Crop Assistance Program (BCAP). EGs covering 75 % of the establishment costs provide high returns for growers on medium to high-productivity sites. Stand-alone AIPs with payments of $124 ha^?1 year^?1 paid over 5–15 years had little impact on profitability for growers but were costly for a funding agency. Low-cost loans with an interest rate of 2–4 % are one of the least expensive approaches ($1.3–6.6 odt^?1) and improve profitability for medium- and high-yielding (8–16 odt ha^?1 year^?1) sites. A matching payment incentive providing $50 per odt delivered was the only individual incentive approach that made low-yielding sites (6 odt ha^?1 year^?1) profitable but was costly per odt compared to other incentives. Current CRP incentives made willow profitable across all productivity scenarios. The BCAP program generates higher profits for all productivity scenarios but comes at a higher cost. Effective financial incentives need to be well designed and monitored so that the target audience is reached and the intended policy goals are attained.     

Composition, Stand Structure, and Biomass Estimates of “Willow Rings” on the Canadian Prairies

Many small wetlands are scattered across the Canadian Prairies. These wetlands are often surrounded by a ring of phreatophytic shrubs, of which willows are the dominant genus. Even though many of these willow rings are currently degraded, due to the lack of disturbance factors such as prairie wild fires and bison herds, they are still of great value as a biomass resource without carbon debt. Our study had the objectives to (1) study the distribution of five native willows (Salix bebbiana, Salix discolor, Salix eriocephala, Salix interior, and Salix petiolaris) in 12 willow wetland communities in relation to a moisture gradient and (2)examine the effects of age of the willow ring on biomass potential, stand structure, and species distribution. Annual biomass production ranged from 1.9 to 16.2 odt ha^?1 year^?1 for the 12 sites that were between 9 and 34 years old. Current standing biomass for the 12 willow rings with a total area of 1.5 ha was estimated at 239.2 odt. With age, stand structure changed from multiple small-diameter stems to fewer large-diameter stems, and at the same time the species distribution shifted from one dominated by S. petiolaris to one being dominated by S. discolor. Additionally, the sympatric willows showed a distribution along a moisture gradient, with S. eriocephala, S. interior, and S. petiolaris in moist locations and S. bebbiana and S. discolor in drier locations.     

Yield of willow (Salix spp.) grown in short rotation coppice mixtures in a long‐term trial

Salix spp. genotypes were grown in random intimate mixtures comprising 5, 10, 15 and 20 components at 3 planting densities (10 000, 15 000 and 20 000 cuttings ha^?1). Planted in 1994/95, plots were harvested every 3 years in 1998/99 (previously reported), 2001/02, 2004/05 and 2007/08. Each individual stool in both mono‐ and mixture plots was weighed. The total yield from mixture plots was consistently higher than the mean of the components in mono‐plots and with only limited exceptions higher than the yield of any of the individual components grown in mono‐plots. This occurred despite the loss of a number of disease‐susceptible genotypes. When a stool died the remaining plants were able to colonise the vacant space and compensate for the loss. There was no clear benefit in increasing the number of components from 10 to 15 or 20 although host diversity is considered to be an important contributor to the effectiveness of a mixture both in disease reduction and yield enhancement. It is argued that the use of Salix spp. mixtures is highly advantageous, even in the absence of any disease pressure, and that mixtures increase the sustainability of a willow plantation.     

Greenhouse Gas Potentials of Shrub Willow Biomass Crops Based on Below- and Aboveground Biomass Inventory Along a 19-Year Chronosequence

Shrub willow biomass crops (SWBC) have been developed as a biomass feedstock for bioenergy, biofuels, and bioproducts in the northeastern and midwestern USA as well as in Europe. A previous life cycle analysis in North America showed that the SWBC production system is a low-carbon fuel source. However, this analysis is potentially inaccurate due to the limited belowground biomass data and the lack of aboveground stool biomass data. This study provides new information on the above- and belowground biomass, the carbon–nitrogen (C/N) ratio, and the root/shoot (R/S) ratio of willow biomass crops (Salix × dasyclados [SV1]), which have been in production from 5 to 19 years. The measured amounts of biomass were: 2.6 to 4.1 odt ha^?1 for foliage, 4.9 to 10.9 odt ha^?1 for aboveground stool (AGS), 2.9 to 5.7 odt ha^?1 for coarse roots (CR), 3.1 to 10.2 odt ha^?1 for belowground stool (BGS), and 5.6 to 9.9 odt ha^?1 for standing fine root (FR). The stem biomass production ranged from 7.0 to 18.0 odt ha^?1?year^?1 for the 5- and 19-year-old willows, respectively. C/N ratios ranged from 23 for foliage to 209 for belowground stool. An average R/S ratio of 2.0, calculated as total belowground biomass (BGS, CR, and FR) plus AGS divided by annual stem biomass, can be applied to estimate the total belowground biomass production of a mature SWBC. Based on AGS, BGS, and CR and standing FR biomass data, SWBC showed a net GHG potential of ?42.9 Mg CO₂ eq?ha^?1 at the end of seven 3-year rotations.     

Shrub Willow (<Emphasis Type="Italic">Salix</Emphasis>) Biomass Crop Performance on Five Sites Over Two Rotations in Michigan,USA and the Implications of Adequate Field Testing to Commercial Producers

Fifteen varieties of willow (Salix) hybrids were observed in a replicated study on five diverse sites in Michigan during the establishment year and over two subsequent 3-year rotations. Sixty-one percent of the total variation in yield observed was due to environmental factors, 11% was due to genetic factors, and the remainder was unexplained. Biomass yield over 6 years ranged from 50.5 oven-dry Mg ha^?1 at one site to 22.9 oven-dry Mg ha^?1 at another. Warmer and wetter sites tended to produce more biomass than colder drier sites, but correlations between yield and other edaphic and climatic factors were less clear. High-yielding varieties tended to be taller, but survival and number of stems per stool were uncorrelated with yield. A cohort of elite varieties selected based on test-wide performance produced up to 26% more biomass than randomly chosen varieties. Cohorts of elite varieties selected based on performance in local tests did better, producing up to 31% more biomass than randomly chosen varieties. Because of ranking changes, selections made after two rotations outperformed those made after only one rotation by as much as 9%. Adequately tested planting stock has the potential to increase the financial return to a willow energy farmer by nearly $100 ha^?1 year^?1. This will multiply rapidly as willow is planted on some of the 700 million hectares of retired cropland in the USA. The nominal cost of breeding and field testing willow energy crops can be easily justified as we proceed to the envisioned billion-ton bioeconomy.     

Fertilization of SRC Willow,II: Leaching and Element Balances

Short rotation coppice (SRC) willow is an emerging cropping system in focus for production of biomass for energy. To increase production, the willow is commonly fertilized, but studies have shown differing effects of fertilization on biomass production, ranging from almost no response to considerable positive effects. Focus has also been on replacing mineral fertilizer with organic waste products, such as manure and sludge. However, the effect on biomass production and environmental impact of various dosage and types of fertilizer is not well described. Therefore we studied the environmental impacts of different doses of mineral fertilizer, manure and sewage sludge in a commercially grown SRC willow stand. We examined macro nutrient and heavy metal leaching rates and calculated element balances to evaluate the environmental impact. Growth responses were reported in a former paper (Sevel et al. “Fertilization of SRC Willow, I: Biomass Production Response” Bioenergy Research, 2013). Nitrogen leaching was generally low, between 1 and 7 kg N ha^?1 year^?1 when doses of up to 120 kg N ha^?1 year^?1 were applied. Higher doses of 240 and 360 kg N ha^?1 as single applications caused leaching of 66 and 99 kg N ha^?1 year^?1, respectively, indicating N saturation of the system. Previous intensive farming including high doses of fertilizer may be responsible for a high soil N status and the high N leaching rates. However, moderate fertilization input could not compensate P and K exports with the biomass harvest. No elevated leaching of heavy metals was observed for any fertilization treatments and more cadmium than applied with the fertilizer was removed with the biomass from the system.     

Stress tolerance of five willow clones after irrigation with different amounts of landfill leachate

Short-rotation willow (Salix sp.) coppice, a commercial crop grown for energy purposes, is used for phytoremediation of landfill leachate in Sweden. However, the leachate's chemical composition can cause plant damage mainly due to high NaCl and NH4 concentrations. A pot experiment was conducted in order to quantify the growth responses of five different willow clones ("78-183", "Jorr", "Loden", "Olof", "Tora") to irrigation with different leachate mixtures (corresponding to 240, 180, and 120 mg Cl l(-1)) and to assess the applicability of leaf length and leaf fluctuating asymmetry as stress indicators. A series of plant traits (shoot, root and leaf dry weight, leaf area, leaf length and leaf fluctuating asymmetry) were measured. The irrigation with leachate resulted in reduced relative growth rates but there were no clear differences between the different concentrations. The clones "Jorr" and "Loden" performed best in terms of differences in relative growth rate between control and leachate treatments. Leaf length appeared to be a useful stress diagnostic tool for use in situ showing a high correlation to growth, whereas fluctuating asymmetry showed no such correlation. Higher N, lower P and higher Na concentrations in plant stems treated with leachate than control plants were observed.     

Species and Genotype Effects of Bioenergy Crops on Root Production,Carbon and Nitrogen in Temperate Agricultural Soil

Bioenergy crops have a secondary benefit if they increase soil organic C (SOC) stocks through capture and allocation below-ground. The effects of four genotypes of short-rotation coppice willow (Salix spp., ‘Terra Nova’ and ‘Tora’) and Miscanthus (M.?×?giganteus (‘Giganteus’) and M. sinensis (‘Sinensis’)) on roots, SOC and total nitrogen (TN) were quantified to test whether below-ground biomass controls SOC and TN dynamics. Soil cores were collected under (‘plant’) and between plants (‘gap’) in a field experiment on a temperate agricultural silty clay loam after 4 and 6 years’ management. Root density was greater under Miscanthus for plant (up to 15.5 kg m^?3) compared with gap (up to 2.7 kg m^?3), whereas willow had lower densities (up to 3.7 kg m^?3). Over 2 years, SOC increased below 0.2 m depth from 7.1 to 8.5 kg m^?3 and was greatest under Sinensis at 0–0.1 m depth (24.8 kg m^?3). Miscanthus-derived SOC, based on stable isotope analysis, was greater under plant (11.6 kg m^?3) than gap (3.1 kg m^?3) for Sinensis. Estimated SOC stock change rates over the 2-year period to 1-m depth were 6.4 for Terra Nova, 7.4 for Tora, 3.1 for Giganteus and 8.8 Mg ha^?1 year^?1 for Sinensis. Rates of change of TN were much less. That SOC matched root mass down the profile, particularly under Miscanthus, indicated that perennial root systems are an important contributor. Willow and Miscanthus offer both biomass production and C sequestration when planted in arable soil.     

Responses of Nondormant Black Willow (Salix nigra) Cuttings to Preplanting Soaking and Soil Moisture

The use of willow cuttings for streambank stabilization is a common practice in riparian ecosystems throughout the United States. Many environmental factors govern the outcome of such planting. However, other factors such as preplanting treatments, planting methods, and physiological status of cuttings (dormant vs. actively growing) may also be crucial in determining the survival of willow cuttings. Actively growing (nondormant) Black willow (Salix nigra) cuttings, 30 cm in length and 1 cm in diameter at the base, were subjected to three soaking treatments (0, 7, and 15 days) prior to planting. Following the initial treatment, cuttings were grown in a greenhouse in pots under three soil moisture regimes (well‐watered but not flooded, permanently flooded, and intermittently flooded). Plant gas exchange, growth, biomass, and survival were measured. Results demonstrated that soaking for 7 days was beneficial to early development of cuttings in the well‐watered (control) soil moisture regime, enhancing percent bud flush and survival significantly. However, 15 days of soaking proved to be detrimental to survival of cuttings irrespective of soil moisture regimes. Results also demonstrated that the beneficial effects of 7‐day soaking were limited to the well‐watered soil moisture regime but not to the flooded or intermittently flooded regimes. Soaking nondormant cuttings may be worthwhile if the planting site is likely to present ample soil moisture but nonflooded conditions to the transplanted cuttings.     

Toxicity of 2,3,5,6-tetrachlorophenol to willow trees (Salix viminalis)

Chlorinated phenols have been intensively investigated from an eco-toxicological point of view, however almost nothing is known about toxicity of tetrachlorophenol (TeCP) to higher terrestrial plants. This article applied the willow tree acute toxicity test to study the toxicity of 2,3,5,6-TeCP to willows Salix viminalis (S. viminalis) at neutral and acidic conditions (roughly pH 7 and 4) with inhibition of transpiration as toxic endpoint. At neutral pH the EC₅₀ was >10 mg L^?1 while the EC₅₀ at acidic conditions was 0.32 ± 0.17 mg L^?1, clearly indicating that toxicity is exerted by the non-ionic chemical fraction. Standard tests running at neutral pH are therefore not capturing the full toxicity of weak acids and bases.