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

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<ul><li><p>Soil-solution chemistry in a coniferous stand afteradding wood ash and nitrogen</p><p>Eva Ring, Staffan Jacobson, and Hans-rjan Nohrstedt</p><p>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 &lt; 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.</p><p>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 &lt; 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.</p><p>[Traduit par la Rdaction] Ring et al. 163</p><p>Introduction</p><p>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</p><p>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).</p><p>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</p><p>Can. J. For. Res. 36: 153163 (2006) doi:10.1139/X05-242 2006 NRC Canada</p><p>153</p><p>Received 17 June 2005. Accepted 12 October 2005.Published on the NRC Research Press Web site at on 25 January 2006.</p><p>E. Ring,1 S. Jacobson, and H.-. Nohrstedt.2 Skogforsk,Forestry Research Institute of Sweden, Uppsala Science Park,SE-751 83 Uppsala, Sweden.</p><p>1Corresponding author (e-mail: address: Swedish Research Council for Environment,Agricultural Sciences and Spatial Planning (FORMAS),Box 1206, 111 82 Stockholm, Sweden.</p></li><li><p>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</p><p>+) may increase the formation ofammonia (NH3) because of the high pH of the ash.</p><p>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.</p><p>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</p><p>aluminum (Al), sulphate (SO42), and nitrate (NO3</p><p>), 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.</p><p>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.</p><p>Materials and methods</p><p>Site descriptionThe 249 Riddarhyttan experimental site is located on a</p><p>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</p><p>and the stand was thinned before the experiment was estab-lished.</p><p>Experimental designTen treatments were tested in a randomized block design</p><p>with three blocks. The results from eight of these treatmentsare reported here (Table 1). Study plots sized 22 m 22 mwere laid out with similar tree basal area and number ofstems per hectare. The blocking was largely based on a prin-cipal components analysis of soil-solution chemistry sampledon two occasions before treatment, but moisture conditionsand some site factors were also taken into consideration. Therandomization within blocks was not complete, which mighthave affected the results from the statistical analyses to someextent. Some plots deviated from the general pattern. The</p><p> 2006 NRC Canada</p><p>154 Can. J. For. Res. Vol. 36, 2006</p><p>Treatment AbbreviationMoisture correctionof dosage (%)</p><p>Control Control 3 Mg crushed, self-hardened ashha1 3Cr 256 Mg crushed, self-hardened ashha1 6Cr 259 Mg crushed, self-hardened ashha1 9Cr 253 Mg pelleted ashha1 3Pel 10150 kg Nha1 N 150 kg Nha1 + 3 Mg crushed, self-hardened ashha1 (simultaneous application) N + Cr 25 (crushed ash)150 kg Nha1 + 3 Mg crushed, self-hardened ashha1 (N applied 1 month before ash) NbeforeCr 25 (crushed ash)</p><p>Note: Two treatments with organic pellets were included in the experimental design but excluded from the present paper. The dosages of ash pellets re-fer to dry masses. Nitrogen (N) was applied as NH4NO3 with some dolomite and boron.</p><p>Table 1. Studied treatments at the 249 Riddarhyttan experiment.</p></li><li><p>treatment regarded as being of the least potential interest, Napplied 1 month before 3 Mg crushed, self-hardened ashha1</p><p>(NbeforeCr), was therefore applied to the most deviant plots.The ash and N were applied manually between 27 and 30September 1995. In treatment NbeforeCr, the N fertilizerwas applied on 1 September.</p><p>Wood-ash characteristicsThe crushed, self-hardened ash originated from the com-</p><p>bustion of fuel consisting of (on average over the season)75% biofuels, 23% petrochemical oil, and 2% pine oil atASSI Kraftliner in Pite, northern Sweden. Bark accountedfor about 50% of the biofuels and logging residues and by-products from sawmills for the remainder. The ash was piledand left to self-harden for about 1 month. It was then crushedand sieved through a 10 mm mesh. A laboratory dry-sievinganalysis of the ash showed that the length of over 60% (bymass) of the ash particles exceeded 2.0 mm. Wet sieving anda simple leaching test revealed that a large proportion of theash was readily soluble in water. According to an X-ray dif-fraction analysis (Siemens D-5000, PSD-detector, 40 kV,20 mA), the crushed, self-hardened ash consisted of Na2SO4,K3Na(SO4)2, Na2SO410H2O, CaCO3, and traces of SiO2,among which the sulphates dissolve readily in water.</p><p>The pelleted ash originated from combustion at the Ortvikenpulp plant. It was pelleted by IKAB AB, Iggesund, including8%10% pine oil as a binding agent. The pellets dissolvedquite readily in water according to the leaching test alreadymentioned but less readily than the crushed, self-hardenedash. The pellets consisted mainly of SiO2, CaCO3, and MgO,but Ca2Al2SiO7, NaAlSi3O8, KAlSi3O8, and probably KCland Fe2O3 were also present.</p><p>Generally, the contents of major elements in the two ashesapplied at experiment 249 were comparable with those ofother wood fuel ashes (n = 121156) as compiled by Steenariand Lindqvist (1997). Compared with these ashes, the crushedash was high in sodium (Na) and sulphur (S), whereas thepelleted ash was rather high in Al (Table 2). Compared withthe ash pellets, the crushed ash had higher concentrations ofNa, potassium (K), S, boron (B), barium (Ba), nickel (Ni),lead (Pb), and vanadium (V) and lower concentrations of Al,iron (Fe), silicon (Si), C, arsenic (As), and mercury (Hg).The high concentrations of Ni and V in the crushed ash wereprobably due to the cocombustion of petrochemical oil. TheN fertilizer was NH4NO3 (27.2% N) with some dolomite andB supplied as colemanite (Table 2).</p><p>Soil-solution samplingSix suction cups were installed in each study plot: three</p><p>Teflon cups (type PRENART Super Quartz supplied byPRENART Equipment ApS, and threeceramic cups as backups. Since the Teflon cups worked ade-quately, the results presented refer solely to the soil solutionsthat they retrieved. The Teflon and ceramic cups in each plotwere installed alternately at fixed cardinal points in a circlewith a diameter of about 6 m at approximately 0.5 m depthin the mineral soil and at an angle of 6070 to the soil sur-face. The sampling depth corresponded to the lower B or up-per C horizon. The Teflon cups were installed in a slurry ofwater and quartz flour that consisted of 99.5% SiO2, 0.15%Al2O3, 0.035% Fe2O3, and 0.05% TiO2 according to the</p><p>manufacturer. The sampled soil solutions were collected in1 L glass flasks, which were buried at 0.5 m depth up to 1 maway from the suction cups. To speed up equilibration withthe soil, the cups were sampled and the collected soil solu-tions were discarded twice. All but one of the Teflon cupswere installed 27 weeks before the sampling commenced,corresponding to 3.5 months prior to the treatments.</p><p>During sampling, a suction of 7080 kPa was applied bymanual pumping and the soil-solution samplers were left tofill for 35 days. The soil-solution samples were collected inacid-washed plastic flasks in the early p...</p></li></ul>


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