Soil-solution chemistry in a coniferous stand after adding wood ash and nitrogen

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  • Soil-solution chemistry in a coniferous stand afteradding wood ash and nitrogen

    Eva Ring, Staffan Jacobson, and Hans-rjan Nohrstedt

    Abstract: Wood-ash applications have been proposed to promote the long-term sustainability of forest production at in-creased harvest intensities. Effects of wood-ash and nitrogen (N) application on soil-solution chemistry were studied for9 years following application in a coniferous stand in Sweden. Crushed, self-hardened wood ash was applied at 3, 6, and9 Mgha1 alone, the lowest dosage both with and without 150 kg Nha1. Pelleted wood ash (3 Mgha1) and N werealso applied alone. The soil solution was sampled by suction cups at 50 cm depth. The crushed, self-hardened ash readilydissolved in water, as reflected in increased soil-solution concentrations of sodium and sulphate. Significant (p < 0.05)elevations were also found for potassium, calcium, aluminum, and total organic carbon. Vanadium, chromium, manga-nese, nickel, copper, zinc, arsenic, and lead were not significantly affected by the ash treatments, but cadmium tendedto increase in the treatments with ash alone. From the fourth year onwards, the pH of the soil solution was loweredand the aluminum concentration raised in the plots given 9 Mg crushed ashha1. Fertilization with N alone temporarilyincreased concentrations of inorganic N, cadmium, aluminum, and zinc and decreased the pH. The crushed ash gener-ally had longer lasting effects than N fertilization.

    Rsum : Des applications de cendre de bois ont t proposes afin de promouvoir la durabilit long terme de laproduction forestire avec des intensits accrues de rcolte. Les effets de lapplication de cendre de bois et dazote (N)sur la chimie de la solution de sol ont t tudis durant les neuf annes suivant lapplication dans un peuplement rsi-neux en Sude. La cendre broye autodurcissante a t applique seule aux taux de 3, 6 et 9 Mgha1; le plus faibledosage a t appliqu seul mais aussi avec 150 kg Nha1. De la cendre granule (3 Mgha1) et N ont aussi t appli-qus seuls. La solution de sol a t chantillonne avec des coupes tension 50 cm de profondeur. La cendre broyeautodurcissante sest rapidement dissoute dans leau comme lindiquaient les concentrations accrues de sodium et sul-fate dans la solution de sol. Des augmentations significatives (p < 0,05) ont aussi t observes pour potassium, cal-cium, aluminium et carbone organique total. Les concentrations de vanadium, chromium, manganese, nickel, cuivre,zinc, arsenic et plomb nont pas t significativement affectes par les applications de cendre mais cadmium avait ten-dance augmenter avec les applications de cendre seule. partir de la quatrime anne, le pH de la solution de sol adiminu et la concentration de aluminium a augment dans les parcelles traites avec 9 Mg de cendre broyeha1. Lafertilisation avec N seul a temporairement augment les concentrations de N inorganique, de cadium, aluminium et zincet a diminu le pH. La cendre broye a gnralement eu des effets plus long terme que la fertilisation avec N.

    [Traduit par la Rdaction] Ring et al. 163


    Biofuels from forest fellings are renewable energy sources,the use of which is consistent with Swedish energy policyand national environmental quality objectives regarding cleanair. The extraction of biofuels from forests sometimes im-plies increasing the harvesting intensity, which may nega-tively affect the long-term sustainability of forest productionand cause unwanted environmental effects. For instance, whole-tree harvesting, that is, the harvesting of all abovegroundparts, poses a greater threat to the long-term sustainability of

    forest production than conventional stem harvesting, whichleaves the logging residues on site, because it increases theamounts of nutrients that are removed (Weetman and Webber1972; Mlknen 1976).

    The burning of forest biofuels produces large amounts ofalkaline ash, which contain most of the inorganic nutrientsand metals, that have accumulated in the trees. Nitrogen (N),on the other hand, is volatilized in combustion and is notpresent in the ash. The composition of the ash generated de-pends on the types of biofuel and boiler involved, the pointwhere the ash is collected within the plant (fly ash or bottomash), and whether additional fuels, such as petrochemical oil,are used. To date, most of the ashes produced in Swedenhave been dumped in landfills, a practice that may causenegative environmental effects on a local scale. It has beensuggested that biofuel ash should be recycled instead, that is,returned to forest land, to promote the long-term sustainabilityof forest production and (or) to counteract anthropogenicacidification. In the short term, however, indications of bothincreases and decreases in stem growth have been found afterwood-ash applications (Jacobson 2003). In a Swedish envi-ronmental impact assessment regarding forest biofuels, Egnell

    Can. J. For. Res. 36: 153163 (2006) doi:10.1139/X05-242 2006 NRC Canada


    Received 17 June 2005. Accepted 12 October 2005.Published on the NRC Research Press Web site at on 25 January 2006.

    E. Ring,1 S. Jacobson, and H.-. Nohrstedt.2 Skogforsk,Forestry Research Institute of Sweden, Uppsala Science Park,SE-751 83 Uppsala, Sweden.

    1Corresponding author (e-mail: address: Swedish Research Council for Environment,Agricultural Sciences and Spatial Planning (FORMAS),Box 1206, 111 82 Stockholm, Sweden.

  • et al. (1998) suggested that the effects of increased harvestintensity should be counteracted by recycling wood ash andthat the demand for N can be met by conventional forest fer-tilization with N when necessary. The timing of fertilizationis likely to be crucial when applying combinations of N fer-tilizer and alkaline ash. Simultaneous application of alkalineash and ammonium (NH4

    +) may increase the formation ofammonia (NH3) because of the high pH of the ash.

    Owing to the potentially adverse effects on both the envi-ronment and human health of applying untreated ash to for-ested sites, it must be stabilized before it is applied toforests. The aim of stabilization is to modify the solubility ofthe ash components and the size of the ash particles, that is,to form dense ash-particle agglomerates (Steenari et al. 1999).Diverse methods for doing this have been tested, for instancepelleting, granulation, and self-hardening and crushing (e.g.Ring et al. 1999). Self-hardening refers to the ability of mostash materials to solidify upon the addition of water (Steenariand Lindqvist 1997). In Sweden, self-hardening followed bycrushing has become the most common method for ash sta-bilization in recent years. However, a laboratory leachingtest on self-hardened wood ashes showed that significantproportions of sodium (Na) and potassium (K) were presentas salts in these ashes and were rapidly released from them(Steenari et al. 1999). Steenari et al. (1999) found that thesimulated short-term release of the Na and K salts was notreduced by any of the stabilization methods applied.

    The environmental effects of recycling biofuel ashes needto be fully understood before the practice can be introducedin Swedish silviculture on a large-scale basis. Over the past15 years, there has been extensive research on recyclingbiofuel ashes (e.g. Egnell et al. 1998; Nohrstedt 2001; Saarsalmiand Mlknen 2001; Lundstrm et al. 2003b; Aronsson andEkelund 2004). However, the great variations in ash chemis-try, stabilization methods used, ash dosage, application dates,and climate complicate the generalization of observed ef-fects (cf. Steenari and Lindqvist 1997; Aronsson and Ekelund2004). Nevertheless, some general effects on forest soil pro-cesses of liming and wood-ash application have been recog-nized. Lundstrm et al. (2003b) reviewed a large number ofliming and wood-ash experiments performed in Europeanand North American forests. They concluded that liming orwood-ash application generally increased the leaching of dis-solved organic carbon (C), decreased the pH in the deepmineral soil solution, and increased the concentrations of

    aluminum (Al), sulphate (SO42), and nitrate (NO3

    ), proba-bly as a result of the high ionic strength that they generatedand increased microbial activity. In another review, Aronssonand Ekelund (2004) identified issues related to aquatic eco-systems and their responses to terrestrial ash applications asimportant topics for future research.

    The present study was initiated to study the effects onsoil-solution chemistry of applying a pelleted wood ash at3 Mgha1 and a crushed, self-hardened wood ash at threedifferent dosages (3, 6, and 9 Mgha1), the lowest dosageboth with and without N.

    Materials and methods

    Site descriptionThe 249 Riddarhyttan experimental site is located on a

    forested slope (approximately 10%) in south-central Sweden(5948N, 1530E). The altitude is 180 m a.s.l. A podzolizedsoil profile has developed on the sandysilty to silty mo-raine. The C/N ratio of the mor layer was 31 in the controlplots and the pH (H2O) was 4.0. The uncorrected annual pre-cipitation is on average 728 mm and the annual temperature4.7 C (Alexandersson et al. 1991). During most of the studyperiod, the annual precipitation was slightly (3%10%) lowerthan the long-term average, while in 1996 and 2000, the pre-cipitation was nearly 20% lower and 40% greater than thelong-term average, respectively (data from the Swedish Me-teorological and Hydrological Institute). The site was coveredby a 60-year-old mixed stand of Pinus sylvestris L. and Piceaabies (L.) Karst. The site quality class was 7.7 m3ha1year1

    and the stand was thinned before the experiment was estab-lished.

    Experimental designTen treatments were tested in a randomized block design

    with three blocks. The results from eight of these treatmentsare reported here (