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The objectives of this study were to estimate biomass production in commercially grown short rotation coppice willow in Denmark and to investigate effects of site and management factors on willow yield. Biomass production assessed by non-destructive sampling on 296 plots from 25 plantations was analyzed using a mixed model approach. Average production in the stands varied between 2.4 and 15.1 odt ha−1 year−1, and average second rotation growth (8.2 odt ha−1 year−1) was significantly higher than first rotation growth (6.5 odt ha−1 year−1). Annual production was significantly correlated with clone, soil texture, soil drainage, fertilization, weeds, rotation number, and shoot age. Further, interactions between clone and soil drainage as well as between clone and soil texture were significant, indicating the importance of a site-specific choice of clones.

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. 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.

Short rotation coppice (SRC) willow is often regarded as one of the most promising crops to increase biomass production and thereby meet the growing demand for renewable energy. This study is based on the hypotheses that biomass production of SRC willow responds positively to increasing doses of nitrogen, and that similar biomass production response can be achieved by use of mineral fertilizer, sewage sludge and animal manure. A 2-year experiment was established with the clone Tordis grown on a sandy soil in northern Jutland, Denmark. The experiment included mineral fertilizer, sludge and manure, and treatments of different doses up to 360 kg nitrogen ha−1. The fertilization led to a modest but significant increase in biomass production. The largest production of 11.9 oven dried tons/ha/year was obtained for the application of 60 kg nitrogen ha−1 annually. Higher doses did not lead to increased biomass production; in fact, production seemed to decline with increasing fertilization application (not significant). We found no difference in production between different types of fertilizers. The limited response of the fertilization may be caused by a high fertility of the soil due to former agricultural fertilization. The number of sagging shoots increased significantly with increasing nitrogen dose. Short rotation coppice (SRC) willow is often regarded as one of the most promising crops to increase biomass production and thereby meet the growing demand for renewable energy. This study is based on the hypotheses that biomass production of SRC willow responds positively to increasing doses of nitrogen, and that similar biomass production response can be achieved by use of mineral fertilizer, sewage sludge and animal manure. A 2-year experiment was established with the clone Tordis grown on a sandy soil in northern Jutland, Denmark. The experiment included mineral fertilizer, sludge and manure, and treatments of different doses up to 360 kg nitrogen ha−1. The fertilization led to a modest but significant increase in biomass production. The largest production of 11.9 oven dried tons/ha/year was obtained for the application of 60 kg nitrogen ha−1 annually. Higher doses did not lead to increased biomass production; in fact, production seemed to decline with increasing fertilization application (not significant). We found no difference in production between different types of fertilizers. The limited response of the fertilization may be caused by a high fertility of the soil due to former agricultural fertilization. The number of sagging shoots increased significantly with increasing nitrogen dose.

Ambitious targets for reducing emissions of carbon dioxide have created a demand for renewable sources of energy. Short rotation coppice (SRC) willow has the potential for meeting part of this demand. In this study, an experiment including four commercial clones of willow grown on two different soil types in northern Denmark is reported. Annual biomass production was estimated after the first and second growing season in the first rotation using a non-destructive method and total biomass production was measured by harvesting of the willow after the second growing season. The non-destructive method showed a large increase in annual biomass production from the first to the second growing season. Based on the harvested willow, average annual biomass production of the four clones ranged from 5.2 to 8.8 odt ha−1 yr−1 with a significant effect of both soil type and clone. The interaction between clones and soil types was also significant, indicating that different clones may be better suited for different soil types. On average, estimates of annual biomass production obtained by non-destructive estimation exceeded those obtained by destructive methods by 1.2 odt ha−1 yr−1. This bias indicates a need to revise commonly used methods for assessment of biomass production in SRC willow.

Harvest of forest biomass for energy production may lead to a significant export of nutrients from the forest. Ash spreading and recycling of nutrients from wood chip combustion to the forest has come into focus as a means for counteracting the nutrient export. This study was carried out to examine the retention of various elements in the different ash fractions and utilise the nutrient recovery to evaluate the fertiliser quality of the examined ash. The mass and element flux of wood chips, bottom ash, cyclone fly ash and condensation sludge at Ebeltoft central heating plant was studied over a four day period in spring 2005. On average, 19 ton wood chips (dry weight) were combusted each day. The combustion of the wood chips produced 0.70% ash and sludge (dry weight). The ash and sludge dry matter was distributed as 81% fly ash, 16% bottom and residual grate ash and 3% sludge solid phase. Substantial amounts of nutrients were retained in the fly ash (P, Ca, Mg, Mn and Cu have a recovery higher than 60% and K, S and Fe have a recovery higher than 30%). The recovery of elements in the bottom ash was smaller. The added recovery of the usable fractions of ashes (both fly ash and bottom ash) exceeded 75% for the nutrients P, Ca, Mn and Mg. Both these ash fractions should be considered for fertilisation.

The area of broadleaved forests is projected to increase in Denmark as well as in the rest of Europe. However, studies of the N leaching response to elevated N deposition have focused on coniferous stands and considerable uncertainty still remains on whether broadleaved and coniferous forests respond differently to elevated N. We studied N input–output relations for eight stands intensively monitored during 2002–2005 and literature data for 37 additional stands which together formed a comprehensive dataset on Danish forests including 26 broadleaved stands and 19 coniferous stands. Nitrate leaching was significantly higher in first generation stands on former arable land with mineral soil C/N ratios 10–15, but both low and high rates were observed independent of the N input. A net N loss was observed in some of these stands even though they are in the aggrading phase and accumulate N in the biomass. Broadleaved stands had significantly lower throughfall N deposition than coniferous stands and this seems to be the main process where forest type exerts an influence on the N cycle. Lower soil C/N ratios offset the effect of throughfall N deposition and thus N leaching did not differ between the two forest types. The best regression models for prediction of nitrate leaching included throughfall N deposition and C/N ratio, but only a minor part of the variability was explained. The C/N ratio of the upper mineral soil was more generally applicable than that of the organic layer. The N retention of the soil was reasonably well predicted above a C/N ratio of 25, but below this threshold the importance is not known. We suggest focusing future efforts on quantifying the relative retention functions (sink strength) of the vegetation and the soil organic matter to improve the predictions of N retention and N leaching.

Canopy litterfall is a significant pathway for return of nutrients and carbon (C) to the soil in forest ecosystems. Litterfall was studied in five even-aged stands of Norway spruce, Sitka spruce, Douglas-fir, European beech and common oak at three different locations in Denmark; two sandy sites, Ulborg and Lindet in Jutland, and one loamy site, Frederiksborg on Zealand. Litterfall was collected during three years from 1994 to 1996 in all five species and during six years from 1994 to 1999 in Norway spruce, Sitka spruce and European beech. The average total litterfall was in the range of 3200–3700 kg ha −1 yr −1 and did not differ significantly among tree species. There were no significant differences in total litterfall among sites during the short period, but during the longer period the richer site Frederiksborg had significantly higher total and foliar litterfall amounts compared to the more nutrient-poor sites Lindet and Ulborg. There were close relationships between foliar and total litterfall suggesting that foliar litterfall can be reliably estimated from total litterfall. Beech and oak bud scale litter was significantly related to foliar litterfall. The amount of branch and twig litter was significantly higher in oak than in other tree species. The average foliar litterfall was well related to the annual volume increment. The relationship differed markedly from previously reported relationships based on global litterfall data suggesting that such relationships are better evaluated at the regional level. Nutrient concentrations and fluxes in foliar litterfall were not significantly different among the five tree species. However, there was a significant effect of site on most nutrient concentrations of the three litterfall fractions, and foliar fluxes of P, Ca and Mn were all significantly highest at Frederiksborg and lowest at Ulborg. The similarity in litterfall inputs to the forest floor under these five tree species suggested that previous reports of large variability in forest floor accumulation should primarily be attributed to differences in litter decomposition.

The mass balance of cadmium in forest ecosystems was parameterized. Soil pH is the main variable controlling retention of Cd in the soil and, hence, determines whether Cd is leached from the system or not. However the extent to which root uptake and biomass accumulation of Cd, or the return of Cd to the soil as internal cycling, influences forest Cd balances is unknown. Also unknown is whether these fluxes might counteract Cd leaching from forest soils. The objective of this study was to compare the Cd mass balance of two contrasting oak forest ecosystems, one grown on an acid sandy soil and one on a near-neutral loamy soil. The oak forest ecosystem grown on the acid sandy soil was a source of Cd with an input flux from deposition of 64 microg Cd m(-2) yr(-1), which was only 30% of the output flux with seepage water (175 microg Cd m(-2) yr(-1)). The oak forest ecosystem on the loamy soil acted as a sink for Cd, with an input flux (92 microg Cd m(-2) yr(-1)) 8.4 times higher than the output flux (11 microg Cd m(-2) yr(-1)). Biomass accumulation was 46% and 74% of root uptake on the sandy and the loamy soil, respectively, indicating that biomass accumulation, if harvested, will reduce the net return to the soil and hence the potential amount of Cd prone for leaching.

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. 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.