ARTICLE

Effects of previous nitrogen fertilization on soil-solution chemistry afterfinal felling and soil scarification at two nitrogen-limited forest sitesEva Ring, Lars Högbom, and Gunnar Jansson

Abstract:Nitrogen (N) fertilization and soil scarification are commonmeasures used in commercial forestry in the boreal zone. Thisstudy was performed to investigate how previous N fertilization in two N-limited Scots pine (Pinus sylvestris L.) stands affected thesoil-solution chemistry after final felling and also to determine the effect of subsequent soil scarification. Nitrogen had been appliedto studyplots at different intervals, resulting in total applications of 0, 450, 900, or 1800kgN·ha−1. Soil-solution sampleswere collectedbefore andafterwhole-treeharvestingof theP. sylvestris stand, fromundisturbed soil andalso afterharvesting fromsoil below furrows,tilts, and areas between furrows created by disc trenching. After harvesting, the K+ concentration was lower at higher N fertilizationintensities. No overall effect on the N concentrations was detected. Electrical conductivity and the concentrations of Na+, K+, Mg2+,Ca2+, Cl−, NO3

−–N, total N, and total C were all affected by soil scarification. The highest concentrations of these variables were foundbelowtilts and the lowest concentrationsbelow furrows. Theexperimentwas repeated, at a lowermonitoring intensity, at a sitewherethe previous total N application amounted to 0 and 450 kg N·ha−1. Here the NO3

−–N concentration responded to disc trenching in asimilar way to that observed in the main experiment. The study shows that previous N fertilization of N-limited forest does notnecessarily affect the soil-solution chemistry significantly after whole-tree harvesting.

Résumé : La fertilisation en azote (N) et le scarifiage du sol sont des traitements couramment utilisés dans les forêts commer-ciales de la zone boréale. Cette étude visait a examiner comment une fertilisation en azote réalisée avant la coupe de deuxpeuplements de pin sylvestre (Pinus sylvestris L.) pauvres en N influençait les caractéristiques chimiques de la solution du sol aprèsla coupe finale et a déterminer les effets du scarifiage qui a suivi. L'azote a été appliqué dans des parcelles expérimentales adifférents intervalles, ce qui a produit des applications totales de 0, 450, 900 ou 1800 kg N·ha−1. Des échantillons de solution dusol ont été prélevés avant et après la récolte par arbre entier des peuplements de pin sylvestre, dans des sols non perturbés etaussi après la coupe au fond, sur la crête et entre les sillons créés par le scarifiage. Après la coupe, la concentration en K+ était plusfaible aux endroits où l'intensité de la fertilisation en N était forte. Nous n'avons pas détecté d'effet général sur la concentrationen N. La conductivité électrique et les concentrations en Na+, K+, Mg2+, Ca2+, Cl−, NO3

−–N, N total et C total ont toutes étéinfluencées par le scarifiage du sol. Les plus fortes concentrations de ces variables ont été observées sous la crête des sillons et lesplus faibles concentrations au fond des sillons. L'expérience a été répétée, avec un suivi moins intense, sur une station où lesapplications de N total avant la coupe correspondaient a 0 et 450 kgN·ha−1. Dans ce cas, la réaction de la concentration enNO3

−–Nau scarifiage par sillon était similaire a celle observée dans l'expérience principale. Cette étude montre que la fertilisation en Nréalisée avant la coupe de forêts pauvres en N n'influence pas nécessairement beaucoup les caractéristiques chimiques de lasolution du sol a la suite d'une récolte par arbre entier. [Traduit par la Rédaction]

IntroductionNitrogen (N) fertilization has been used in commercial forestry

for several decades (inter alia Swedish Forest Agency 2012). Be-sides increasing tree growth, N fertilization affects soil and waterboth in the short term and sometimes over a longer term. In ameta-analysis, N application was found to accelerate the leachingof K+, Mg2+, and Ca2+ over time periods less than 5 years (Lucaset al. 2011). Temporary decreases in pH and elevated concentra-tions of NO3

−, NH4+, Al, Zn, and Cd have been recorded in soil

solution after application of 150 kg N·ha−1 (Ring et al. 2006), indi-cating increased leaching of these elements. In the longer term,the incorporation of fertilizer N into the soil (Melin and Nômmik1988) may affect the N-leaching rate after final felling, as sug-gested by Tamm et al. (1974), who studied a fertilized spruce forestgrowing on old arable land before and after clearfelling (Tammand Popovi=c 1974). Final felling alone has been shown to increaseN leaching (Gundersen et al. 2006), but previous N fertilizationmay increase this further. An elevated NO3

− leaching typicallyincreases the leaching of base cations and Al (inter alia Aber et al.

1989). Increased concentrations or leaching rates of NO3− have

been reported after harvesting at two low-productivity forestsites, from study plots that had previously been treated withNH4NO3 amounting to a total of 730 kg N·ha−1 or more, with someadditional nutrients (Ring 1996; Berdén et al. 1997). At the siteexamined by Ring (1996), the NO3

− concentration in the soil solu-tion tended to increase with increasing levels of N application,coinciding with decreasing C:N ratios in the mor layer (Nohrstedt1990). In contrast, NO3

− leaching after final felling of a high-productivity spruce stand was reportedly lower from previouslyurea-fertilized plots than from unfertilized plots; this seemed tobe related to a difference in ground-vegetation biomass (Ring et al.2003). Ground vegetation has been found tomitigate soil-solutionNO3

− concentrations in other studies (Gundersen et al. 2006). Atanother also high-productivity site, the soil-solution concentrationsof NO3

− were not significantly different in plots that had receivedhigh loads of urea prior to harvesting compared with unfertilizedplots (Ring et al. 2001). These studies indicate that the postfellingeffects ofN fertilization onN leaching are influencedby the fertilizer

Received 10 September 2012. Accepted 18 February 2013.

E. Ring, L. Högbom, and G. Jansson. Skogforsk, The Forestry Research Institute of Sweden, Uppsala Science Park, SE-751 83 Uppsala, Sweden.

Corresponding author: Eva Ring (e-mail: eva.ring@skogforsk.se).

396

Can. J. For. Res. 43: 396–404 (2013) dx.doi.org/10.1139/cjfr-2012-0380 Published at www.nrcresearchpress.com/cjfr on 17 April 2013.

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regime and site productivity. However, since the studies currentlyavailable represent only a few site-productivity classes and fertilizerregimes, further investigations are needed.

Soil scarification following the final felling of previouslyN-fertilized stands has the potential to affect N leaching, since asubstantial part of the N applied at fertilization is retained in thesoil (Nohrstedt 1990). Soil scarification, by disc trenching, mound-ing, or other mechanical methods, creates different types of soildisturbance; for instance, it exposes mineral soil and inverts,mixes, and buries the organic layer below a layer of mineral soil.This affects the flows of nutrients and water and the vegetationdevelopment within the patches of soil that have been disturbed(Johansson 1994; Smolander et al. 2000; Palviainen et al. 2007;Tanskanen and Ilvesniemi 2007). For instance, higher NH4

+ con-centrations have been recorded in water collected from belowtilts than below furrows (Piirainen et al. 2007). The combinedeffect of such soil disturbances on nutrient leaching to surfacewater is still unclear, as is the impact of previous fertilization.

Assessing the contributions of individual forestry measures orinteractions within a series of consecutive measures requireslong-termfield experiments, often extending over several decadesin boreal forests. The present study was initiated to examine howprevious N fertilization of two Pinus sylvestris L. (Scots pine) standsaffected the soil-solution chemistry after final felling; in addition,the effect of disc trenching after felling was investigated. Twofield experiments located in N-limited ecosystems were consid-ered: of these one was monitored more intensively. Results fromearlier investigations at these sites have been presented byNohrstedt (1988, 1989, 1998), Högbom and Nohrstedt (2000), andJacobson and Pettersson (2001, 2010). A soil study conducted 1 yearbefore harvesting at one of the sites showed that the C:N ratio ofthe mor layer decreased with increasing total N load, whereas theconcentrations and contents of N and exchangeable Mg2+ and Pincreased (Ring et al. 2011). The concentration and content of ex-changeable K+ decreased in the mor layer and in the upper min-eral soil with increasing N load. In the present study, weinvestigated the soil-solution chemistry before and after final fell-ing, focusing on the period after final felling. We suggest thatafter final felling and soil scarification, the soil solution NO3

−

concentration is themain driver for effects on soil-solution chem-istry. Thus, our main hypotheses were

1. The NO3−–N concentration following final felling increases

with increasing N fertilization intensity. The increase is nega-tively related to the C:N ratio in the mor layer.

2. The effects of disc trenching are more pronounced with in-creasing N-fertilization intensity. In disc-trenched areas, theNO3

−–N concentration in soil solution is highest below tilts,then in areas between furrows, and then below furrows.

Materials and methodsThe study was performed at two field sites in Sweden, 165 Hag-

fors (60°00=N, 13°42=E) and 132 Nissafors (57°24=N, 13°37=E), here-after referred to by the location name alone. The experimentswere established on podzolized soil in P. sylvestris stands growingon a gentle slope with sandy-silty till (Hagfors) or a sandy sedi-ment (Nissafors). The site-quality class was 5.9 m3·ha−1·year−1 atHagfors and 5.5 m3·ha−1·year−1 at Nissafors. Annual precipitationaverages 671 mm in the Hagfors area and 853 mm in the Nissaforsarea, and the annual mean air temperatures are 3.5 and 5.4 °C,respectively (Alexandersson and Eggertsson Karlström 2001). AtHagfors, the precipitation during the study period was about800 mm in 2006, 730 mm in 2007, 790 mm in 2008, 840 mm in2009, and 740 mm in 2010. During May to November of theseyears, i.e., when most of the soil-solution samples were collected,precipitation varied between 480 and 730 mm. The precipitationin July of 2009 was exceptionally high: 260 mm compared with

the 30-year mean of about 80 mm (Alexandersson and EggertssonKarlström 2001). The annual mean air temperature was highest in2008 (5.9 °C) and lowest in 2010 (2.3 °C). In the Nissafors area, theannual precipitationwas 870mmin2006, 940mmin2007, 1040mmin 2008, and 800 mm in 2009 (data from a nearby recording stationoperated by the Swedish Meteorological and Hydrological Institute).The annual mean air temperature ranged from 6.2 to 7.1 °C. Thedeposition of inorganic N was about 6–9 kg N·ha−1 in both studyareas (http://www.krondroppsnatet.ivl.se/).

Experimental designTheHagfors andNissafors experiments were established in 1981

and 1977, respectively, to study the effects on stem-wood growthof different N-fertilization regimes, with andwithout the additionof other nutrients. The observed increases in stem-wood growthagreed with expected values (Pettersson 1994; Jacobson andPettersson 2010). Both experiments used a randomized block de-sign with three replicates of each fertilizer regime. Study plotswere 30 m × 30 m, except for one block at Nissafors that had25 m × 25 m plots. Each study plot was divided into two equallysized parts to which either scarification or no scarification treat-ment was randomly assigned (Fig. 1).

From Hagfors, the control (0N) and three out of six fertilizerregimes were included in the present study and, from Nissafors,the control and one out of five regimes. At Hagfors, the fertilizerapplication started in 1981. Ammonium nitrate (NH4NO3) was ap-plied at a rate of 150 kg N·ha−1 (150N) at 8-, 4-, or 2-year intervalsresulting in total applications of 450 kg N·ha−1 (450N), 900 kg N·ha−1

(900N), and 1800 kg N·ha−1 (1800N), respectively. At the time ofeachN application, 1 kg B·ha−1 was also added. From 1991 onwards,the commercial fertilizer Skog-CANwas used, containing NH4NO3

and dolomite (27% N, 5% Ca, 2% Mg, and 0.2% B). The study plotsrepresenting the 1800 N regime had received varying amounts ofother nutrients (for further details see Ring et al. (2011)). At Nissa-fors, the plots in blocks 1 and 2 were fertilized with 75 kg N·ha−1·year−1 in 1977 and 1978, whereas the plot in block 3 was fertilizedsix times with 25 kg N·ha−1 in 1977. In 1984 and 1989, a singleapplication of 150N was made to each plot, with the addition of20 kg P·ha−1 in 1989. Thus, the total application amounted to450 kg N·ha−1. More details regarding the experiments are pro-vided by Ring et al. (2011).

The tree stands, including stems, tops, and branches, were har-vested in 2006; in March at Hagfors and in early May at Nissafors.Soil scarification was performed by disc trenching in May 2006using amachine equippedwith two rotating discs at the rear. Fourdifferent subplot treatments were identified, namely, no scarifi-cation (in the nonscarified part of the main plot) and, in the disc-trenched part, furrows, tilts, and areas between two furrows,hereafter referred to as “between furrows” (Fig. 1). The scarifica-tion at Hagfors was deeper than at Nissafors (Table 1). At bothsites, the study plots were replanted with 1.5-year-old container-ized P. sylvestris seedlings in late May to early June 2006. Unlike atHagfors, the Nissafors experiment was fenced in June 2006, toavoid browsing on the planted seedlings by large wild herbivoressuch as deer and moose.

Soil-solution chemistrySoil solution was collected from the lower B or upper C horizon

using ceramic suction cups (type P80, CeramTec AG, Germany)(Fig. 1). Each cup was installed at an angle of approximately 75°and connected to a 1 L glass bottle.

Before harvesting (inMay 2005), three cupswere installed in thepart of each main plot, representing the 0N, 450N, and 900Nregimes, that was not to be scarified (Fig. 1). Soon after harvestingand disc trenching, another three cups were installed in this part(in late May to early June 2006). At the same time, nine cups wereinstalled in the scarified part of each plot; three cups below fur-rows, three cups below tilts, and three cups in the area between

Ring et al. 397

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furrows (Fig. 1). These cups were installed in the center of eachsubplot treatment. In addition, three cups were installed in thenonscarified part of each main plot representing the 1800N re-gime at Hagfors.

For sampling, a suction of 75 cbar was generated, and soil-solution samples were collected, on average, 3 days later. Beforeharvest (in late October tomid-December 2005), soil-solution sam-ples were collected on two (Hagfors) or three (Nissafors) occasionsand chemically analyzed. These samples were collected about8 years (in the 450N regime) or 4 years (in the 900N regime) afterthe last N application at Hagfors, and 16 years after the last appli-cation at Nissafors. After harvest and disc trenching, soil solutionwas collected on 23 occasions at Hagfors in the period 2006–2010,and on 10 occasions at Nissafors in the period 2006–2009. Twoadditional samplings were undertaken at Hagfors in late Augustand October 2011 to establish whether the NO3

−–N and NH4+–N

concentrations remained at low levels.The samples collected before harvest at Nissafors were pooled

plotwise before analysis of NO3−–N only, whereas the samples

collected after harvest were analyzed individually for pH andNO3

−–N. One-third of the potential number of samples from Nis-safors collected after harvesting were missing or contained toosmall a volume (<50 mL). This was probably because of the well-drained sandy soil.

The chemical analyses of 18 variables in the Hagfors sampleswere performed on composite samples. These were prepared inthe laboratory by combining equal sample volumes retrievedfrom each of the three cups representing the same subplot treat-ment: nonscarified soil with cups installed either before (one sam-ple) or after (one sample) harvesting, furrows (one sample), tilts

(one sample), and the area between furrows (one sample). Of thetotal number of composite samples, 84% originated from all threecups, 13% from two cups, and 3% from one cup.

Electrical conductivity was measured using a conductivity me-ter equipped with a conductivity electrode. The pH was measuredpotentiometrically at 20 ± 2 °C using a combination pH electrode.Elemental concentrations of Na+, K+, Mg2+, Ca2+, Al, Mn, Cd, andZn were determined by inductively coupled plasma-mass spec-trometry with an ICP-MS-DRC during the first study years andlater by ICP-AES. Concentrations of Cl−, F−, NO2

−–N, NO3−–N, and

SO42––S were determined by anion chromatography. Ammonium

(NH4+–N) was measured by flow injection analysis (FIA). Total N

(TN) was also determined by FIA after oxidation to NO3− using

alkaline peroxodisulfate. Total C (TC) was determined using a TOCanalyzer. The samples collected in 2011 were only analyzed for pH,anions, and NH4

+–N.

StatisticsThe soil-solution chemistry data collected after final felling and

soil scarification were analyzed with the following mixed linearmodel, using the MIXED procedure in SAS/STAT version 9.2 TSLevel 2M3 (http://www.sas.com):

[1] yijklm � � � �i � �j � dij � �k � (��)ik � �l � (��)il

� (��)kl � (���)ikl � (���)ijl � (���)ijl � eijklm

where yijklm is the concentration, electrical conductivity, or pH ofthe soil solution; � is the overall mean; �i is the fixed effect of Nregime i, where i = 0N, 450N, or 900N for the Hagfors data, andi = 0N or 450N for the Nissafors data; �j is the fixed effect of theblock, where j = 1, 2, or 3 for both sites; dij is the random effect ofthe interaction between the N regime and the block (i.e., themain-plot effect); �k is the fixed effect of sampling time k, where kis the time since scarification; (��)ik is the fixed effect of the inter-action between the N regime and sampling time; �l is the fixedeffect of scarification, where l = no scarification, furrows, tilts, orbetween furrows; (��)il is the fixed effect of the interaction be-tween theN regime and scarification; (��)kl is the fixed effect of theinteraction between scarification and sampling time; (���)ikl is thefixed effect of the interaction between the N regime, scarification,and sampling time; (���)ijl is the random effect of the N regime,scarification, and the block; and eijklm is the residual term, wherem = 1 or 2 (number of samples per subplot).

Fig. 1. Schematic outline of the study plots. Suction cups installed in the forest before harvesting are represented by open triangles and cupsinstalled after harvesting and disc trenching by solid triangles. A cross section of disc-trenched soil is given to the right, showing three typesof soil disturbance investigated in this study. Suction cups were installed at a depth of 40–45 cm (lower broken line) from the original uppermineral soil surface (upper broken line).

Table 1. Average measurements, with standard deviations in paren-theses, of the furrows, tilts, and areas between two furrows created bydisc trenching.

Subplot treatment Measurement Hagfors (m) Nissafors (m)

Furrows Depth 0.17 (0.041) 0.062 (0.028)Width 0.70 (0.091) 0.63 (0.072)

Between furrows Width 0.72 (0.087) 1.2 (0.061)Tilts Height 0.21 (0.039) 0.13 (0.048)

Width 0.63 (0.079) 0.57 (0.10)

Note: The measurements were made in 2006, in May at Hagfors and in No-vember at Nissafors, at the locations of the suction cups. Hence, 27 measure-ments for each subplot treatment were made at Hagfors and 18 measurementsat Nissafors.

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The interdependence of repeated measurements was estimatedby applying a spatial covariance structure to model residuals(�2tikl), in which the interdependence of sampling occasions ()declines with increasing time interval (tikl). The denominator de-grees of freedom for the tests of fixed effects were estimatedaccording to the containment method. Differences between least-squares means, adjusted for multiple comparisons according toTukey, were used to test whether treatment effects were signifi-cantly different. To analyze the interactions with time, the sliceoption was used to determine the sampling occasions that exhib-ited effects of either N regime or scarification. Furthermore, thecombined effect of scarification (�l) was analyzed according toModel 1, where l = no scarification or scarification; the latter in-cluded all data collected in the scarified part, i.e., from furrows,tilts, and between furrows. However, to produce results that coulddemonstrate plausible effects on groundwater chemistry, the lat-ter analysis requires that each soil disturbance type covers similarproportions of the regeneration area and that percolation ratesremain largely unaffected.

To be able to evaluate the effect of all N regimes at Hagfors,including the 1800N treatment, a modified version of Model 1,referred to as Model 2, was applied to the data collected only fromthe nonscarified parts of the study plots. Model 2 was the same asModel 1 but without all effects including scarification.

In the ANOVAs, concentrations below the limits of chemicaldetection were allocated values equivalent to half these limits. Inthe Hagfors data set, collected after harvesting during 2006– 2010,all or nearly all (>98%) concentrations of Ca2+, Mn, Na+, Zn, TN,Cl−, SO4

2––S, and TC were above or at the limit of chemical detec-tion. The percentages of concentrations below the limit of detec-tion were 6% for K+, 4% for Mg2+, 39% for Al, and 39% for NO3

−–N.In the Nissafors data set, collected after harvesting during 2006–2009, 9% of the NO3

−–N concentrations were below the limit ofchemical detection. Statistical significancewas defined as p< 0.05.

Logarithmically transformed concentrations were generallyused in the ANOVAs, since this improved the normal distributionof residuals.The least-squaresmean (lsm)concentrationspresented arereconverted from least-squares means based on logarithmicallytransformed concentrations (lsmlog10), correcting the values for log-arithmic bias according to lsm � 10lsmlog 10�residual/2 (cf. Baskerville1972). However, the least-squares means presented graphically wereobtained by running Model 1 or 2 using untransformed values.

Results

Before harvestingNo statistically significant effect of previous fertilization (0N,

450N, or 900N regimes) was detected using Model 2 for the soilsolution collected below the P. sylvestris stand at Hagfors (in No-vember and December of 2005); the only significant effect was ofsampling time (�k) for the concentrations of Na+, Ca2+, and TC. Nosamples were collected from the plots representing the 1800Nregime. When data from all treatments and both samplings wereincluded (n = 18), the median pH was 5.1 and the median concen-trations were 2.0 mg Na+·L−1, 0.49 mg K+·L−1, 0.39 mg Mg2+·L−1,0.53 mg Ca2+·L−1, <0.05 mg Al·L−1, 2.6 mg Cl−·L−1, 1.0 mg SO4

2––S·L−1, <0.1 mg NH4

+–N·L−1, <0.05 mg NO3−–N·L−1, 0.14 mg TN·L−1,

and 4.6 mg TC·L−1. In the soil solution below the P. sylvestris standat Nissafors, the NO3

−–N concentration was below 0.05 mg·L−1 inall samples collected in late October to mid-December 2005.

After harvesting and disc trenchingAfter harvesting and disc trenching, more than 96% of the con-

centrations of F−, Br−, and NO2−–N were below their limits of

chemical detection, i.e., <0.2 mg F−·L−1, <0.2 mg Br−·L−1,and <0.1 mg NO2

−–N·L−1, and 90% of the concentrations of NH4+–N

were below 0.1 mg·L−1. The Cd concentration was determined only

in the samples collected in 2006 and 2007. In 98% of these sam-ples, the concentration was ≤0.1 �g Cd·L−1.

Hagfors 0N, 450N, and 900NTo test how the combined samples that did not include samples

from all three cups affected the statistical results, Model 1 wasapplied after excluding all data originating from only one or twosuction cups. The p values obtained were similar, or indicated thesame effect, as those based on the entire data set with the excep-tions of pH and Cl− (Table 2). However, when comparing the plotsby eye of the least-squares means for pH and Cl−, respectively,between the different data sets (cf. Fig. 2), there was no majordifference in the results.

Only the K+ concentration was affected by the N regime (�i)according to Model 1 (Table 2). The K+ concentration was lower(p = 0.02) in the 900N treatment than in the 0N treatment. Aneffect of the N regime was indicated for the Mg2+ and Zn concen-trations (p < 0.08, Table 2); the Mg2+ concentration tended to behigher in the 900N regime than in the 450N regime, whereas theopposite appeared to be the case for the Zn concentration. Aninteraction between the N regime and sampling time was foundfor six variables (Table 2). The TN concentration for 2006–2010exhibited a temporal pattern similar to that for NO3

−–N concen-tration. The NO3

−–N concentration in the 0N, 450N, and 900Nregimes started to rise, from nearly zero, during the first growingseason following harvest, continuing through the second year(Fig. 2). Thereafter, the concentrations progressively decreased inthe 0N and 900N regimes, whereas in the 450N regime the con-centration remained higher than the other regimes until the lastsampling in 2010, when the concentrations were similar in all Nregimes. This pattern was also apparent in August and October2011 (data not shown). However, when all N regimes (0N up to1800N) were analyzed according to Model 2, the interaction withsampling timewas found early in the study andwasmanifested asan elevation in NO3

−–N concentration in the 1800N regime. Thus,different responses were observed. The increased levels in the450N regime (Fig. 2) seem to have been caused by the high con-centrations recorded below tilts; the mean concentration belowtilts in the 450N regime varied between 2.6 and 5.5mg NO3

−–N·L−1

during August, 2008 and August 2010.A difference in pH or electrical conductivity between N regimes

was found on two occasions. The temporal pattern for the concen-trations of K+ and Cl− was similar among N regimes, but the con-centrations in the 450N and 900N regimes were generally lowerthan in the 0N regime (Fig. 2). The Cl− concentration decreasedprogressively over time, reaching about 20% of the concentrationmeasured soon after harvesting by the end of the study.

Scarification affected electrical conductivity and the concentra-tions of Na+, K+, Mg2+, Ca2+, Cl−, NO3

−–N, TN, and TC (Table 2).Generally, the concentration or electrical conductivity was lowestbelow furrows and highest below tilts (Table 3, Fig. 3). Further-more, the conductivity and the concentrations of Na+, K+, Cl−, TN,and TCwere lower below furrows comparedwith undisturbed soil(no scarification). An interaction between scarification and sam-pling time was detected for 11 variables (Table 2). For Mn, therewas also an interaction between the N regime and scarification.Temporal development differed among the studied variables(Fig. 3). After about 1.5 years, the K+ concentration below furrowswas lower than the concentrations in the other scarification treat-ments. The SO4

2––S concentration started to exhibit differencestowards the end of the study, with the highest concentrationsbelow tilts and the lowest below furrows. The same pattern wasfound during the two samplings in 2011. The NO3

−–N and TNconcentrations exhibited elevated levels below tilts during thelatter part of the study (Fig. 3). In nonscarified soil, the NO3

−–Nconcentration appeared to exceed the concentrations below fur-rows and in areas between furrows late in the study. In August of2011, the highest NO3

−–N concentration (0.5 mg N·L−1) was found

Ring et al. 399

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thecon

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−1),w

hereas

Table 2. p values according to the mixed ANOVA (Model 1) performed on the soil-solution chemistry data collected after harvesting and disc trenching at Hagfors (2006–2010) and Nissafors(2006–2009), including the nitrogen (N) regimes 0N, 450N, and 900N at Hagfors and 0N and 450N at Nissafors. “time” refers to sampling time (i.e., time since scarification).

Factor

Hagfors Nissafors

Electricalconductivity pH* Na+ K+ Mg2+ Ca2+ Al Mn Zn Cl−* SO4

2––S* NO3−–N* TN TC H+ NO3

−–N

N regime 0.41 0.72 0.30 0.024 0.076 0.76 0.50 0.75 0.064 0.13 0.15 0.45 0.46 0.88 0.92 0.32N regime×time <0.0001 <0.0001 0.092 <0.0001 0.89 0.83 0.53 0.80 0.15 0.029† 1.0 0.0004 0.0005 0.95 0.78 0.058Scarification <0.0001 0.46 <0.0001 <0.0001 <0.0001 0.0003 0.39 0.83 0.31 <0.0001 0.18 0.0033 0.0004 0.0016 0.0005 0.0003Scarification×time <0.0001 0.27‡ <0.0001 <0.0001 <0.0001 0.0004 0.68 0.0090 0.61 <0.0001 0.0032 <0.0001 <0.0001 0.0066 <0.0001 <0.0001N regime×scarification 0.26 0.21 0.70 0.54 0.79 0.41 0.11 0.029 0.46 0.60 0.87 0.24 0.15 0.26 0.61 0.66N regime×scarification×time 0.62 1.0 0.26 0.90 0.76 1.0 0.39 1.0 0.83 0.97 0.84 0.065 0.48 0.71 0.0017 0.064Time <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001 <0.0001Block 0.11 0.42 0.67 0.50 0.028 0.12 0.34 0.14 0.30 0.99 0.11 0.093 0.31 0.15 0.52 0.92

Note: Sixteen percent of the data from Hagfors was derived from one or two cups instead of three cups.*Similar p values were also obtained when including the data from the two samplings performed in 2011.†In the ANOVA including only combined samples from three cups, the p value was 0.67.‡In the ANOVA including only combined samples from three cups, the p value was 0.0073.

Fig.2.Least-squ

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the K+ concentration was lower (0.88 mg·L−1) in scarified soil thanin undisturbed soil (1.2 mg·L−1). There was an interaction betweenscarification and sampling time for electrical conductivity andalso for the concentrations of Na+, Mg2+, Ca2+, Mn, Cl−, SO4

2––S,NO3

−–N, TN, and TC. A high Mn concentration in nonscarified soilwas recorded in July 2009, when precipitation was exceptionallyhigh.

Hagfors 1800NWhen examining data only from the nonscarified part of the

plots representing the 0N, 450N, 900N, and 1800N regimes, aneffect of the N regime was detected with respect to pH and to theconcentrations of K+ and Mn. The pH in the 1800N regime waslower than in the 450N regime. The K+ concentration in the 1800Nregime was lower than in all the other N regimes. The mean K+

concentration for the study period was 1.3 mg·L−1 in the 0N,1.1 mg·L−1 in the 450N, 0.95 mg·L−1 in the 900N, and 0.21 mg·L−1 inthe 1800N regime. Finally, the Mn concentration in the 1800Nregime was higher than the concentrations in the 450N and 900Nregimes. An interaction with sampling time was found for electri-cal conductivity and for the concentrations of Na+, K+, Mg2+, Cl−,NO3

−–N, and TN. There was an effect of block on electrical con-ductivity, pH, and the concentrations of Al, Mg2+, Mn, and Zn, andall variables showed an effect of sampling time.

Nissafors 0N and 450NAs for the Hagfors data, no effect of N regime could be detected

for the NO3−–N concentration, whereas scarification did have an

effect (Table 2). The concentration below tilts exceeded the con-centration in all other subplot treatments (Table 3). The NO3

−–Nconcentration (Fig. 4) developed in a similar way over time as atHagfors (Fig. 3). For theH+ concentration, therewas an interactionbetween the N regime, scarification, and sampling time. Such aninteraction was also indicated for NO3

−–N.

DiscussionThe concentration of inorganic N is typically low in the soil

solution below boreal and boreonemoral coniferous forests (interalia Ring et al. 2006). The application of N fertilizer (150N) raises theNO3

− concentration in the soil solution for about a year (Ring et al.2006), whereas intensive N fertilization (i.e., 3 × 600 kg N·ha−1) mayalso increase the NO3

− concentration in the longer term (Nohrstedtet al. 1994). In the present study, the concentration of inorganic N inthe soil solution was low before harvesting and no effect of previousfertilization was found.

Final felling typically increases the NO3− concentration in soil

solution and the NO3− leaching rates for some years (Futter et al.

2010). At Hagfors and Nissafors, the NO3−–N concentrations ob-

served in undisturbed soil following final felling were low com-pared with international data (Gundersen et al. 2006), but atsimilar levels to those found in two comparable studies on low- orintermediate-productivity sites in Sweden (Futter et al. 2010). Theharvesting of tops and branches could have contributed to the lowlevels (Staaf and Olsson 1994).

The soil study performed before harvesting revealed that theC:N ratio in the mor layer decreased with increasing intensity offertilization, whereas the concentration and content of N in-creased (Ring et al. 2011). We did not detect an overall effect of theN regime on the soil-solution NO3

−–N concentration at either Hag-fors or at Nissafors, providing no support for our hypothesis thatthe NO3

−–N concentration would increase with increasing fertil-ization intensity and, consequently, at decreasing C:N ratio in themor layer. This contradicts the findings froma similar study in theboreal part of Sweden (Nohrstedt 1990; Ring 1996). There were noapparent differences between the N regimes 0N, 450N, and 900Nas regards to field-layer species composition and total biomassthat could explain the observed results (L. Högbom, personal com-munication, 2012).

After final felling, only the K+ concentration clearly reflectedthe changes in soil chemistry caused by N fertilization recordedbefore harvesting (Ring et al. 2011). There are several possibleexplanations for the low correspondence between preharvest soilchemistry and postharvest soil-solution chemistry. One explana-tion could be that the soil chemistry was measured in the morlayer and in the upper 20 cm of the mineral soil, whereas the soilsolution was collected at a depth of 40–45 cm. At this depth,effects in the upper soil could have been mitigated by biologicaluptake and by low mobility down the profile (for Mg2+, Ca2+, andP). Furthermore, extracting the soil samples with ammonium lac-tate may have released fractions more tightly bound to the soilmatrix than when collecting soil solution using suction cups. ForK+, however, the effect on the soil store of K+ was apparentlystrong enough to affect the soil-solution concentration below themain rooting zone, possibly facilitated by the high mobility of K+

in soil. It is notable that the K+ concentrations before harvestingdid not differ significantly among the N regimes in the soil solu-tion (0N to 900N), but after harvesting, differences did emerge. Ina previous study, increased concentrations of K+, Ca2+, Al, Zn, andCd were detected or indicated during the first 1–2 years after asingle application of 150N (Ring et al. 2006). The results fromHagfors show that the decline in soil-solution K+ concentrationwas more pronounced at increasing application intensity. Thissuggests that K+ had been leached repeatedly in conjunction withapplication of N fertilizer. The reduction in K+ concentration sup-ports the findings of Lucas et al. (2011).

Judging from the number of statistically significant effects(Table 2), scarification affected soil-solution chemistry to a higherdegree than N regime (0N to 900N). Fertilization induces chemicalchanges in the soil, whereas scarification changes the soil profilephysically. The tilts consisted of inverted soil from the furrows,superimposed on the original mineral soil surface (Fig. 1). Thisdecreased the element store in the furrow soil profiles and corre-spondingly increased the store in the tilt soil profiles. The reducedconcentrations of some elements, most notably K+, below furrowscould reflect the removal of the upper soil (Fig. 3).

Since disc trenching increases variations in microtopographyand exposes mineral soil, small-scale hydrology and soil erosioncould be affected. At high precipitation intensities, water and soilparticles could have been transported from at or near the surfaceof the tilts to the furrows. In addition, at greater soil depth thewater flow could have a horizontal component resulting fromgradients inwater content. However, given the sandy soils and thegentle slope at both Hagfors and Nissafors, the water flow is likelyto have beenmainly vertical in the rooting zone of the study plots.Since the soil solution was collected at a fixed depth from the

Table 3. Mean concentrations over the study period calculated by theleast-squares method for the chemical variables that showed a signif-icant response to scarification (�l) in Table 2.

Site Variable UnitNoscarification Furrow

Betweenfurrows Tilt

Hagfors Electricalconductivity

�S·cm−1 20a 15b 21a 27c

Na+ mg·L−1 0.78a 0.49b 0.97a 1.5cK+ mg·L−1 1.1a 0.51b 1.1a 1.1aMg2+ mg·L−1 0.22a 0.21a 0.32b 0.50cCa2+ mg·L−1 0.38a 0.44a 0.45a 0.71bCl− mg·L−1 1.1a 0.81b 1.4c 2.2dNO3

−–N mg·L−1 0.15ab 0.069a 0.12ab 0.28bTN mg·L−1 0.54ac 0.28b 0.42ab 0.78cTC mg·L−1 3.1a 2.2b 2.9ab 3.8a

Nissafors NO3−–N mg·L−1 0.31a 0.13a 0.49a 3.0b

Note: Since no interaction between N regime and scarification was detected,the means presented were calculated using data from all N regimes included inthe analysis. Values on the same row denoted by different letters show a signif-icant difference.

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Fig. 3. Least-squares mean concentrations in soil solution by scarification treatment at Hagfors. “×” indicates a sampling occasion with a significantdifference (p < 0.05) between treatments. Since no interaction between the N regime and scarification was detected, the means presented werecalculated using data from all N regimes included in the analysis. No scarification (- – -), furrows (o), area between furrows (Œ), and tilts (Œ).

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original soil surface (Fig. 1), disc trenching affected the soil depthabove the suction cups and, as a result, may have influenced theaccumulated surface area of soil particles in contact with perco-lating water, the water residence time, and water content. Thiscould help explainwhy the highest concentrations were generallyfound below tilts and the lowest below furrows. In addition, therate of decomposition is greater within tilts compared with non-scarified soil (Lundmark-Thelin and Johansson 1997), which couldaffect soil-solution chemistry. In a study from Finland, dissolvedorganic carbon (DOC) and NH4

+–N in water collected below theupper B horizon were found to be higher below tilts than belowfurrows created by disc trenching (Piirainen et al. 2007). Similarresults were found for TC in the present study (Table 3). Piirainenet al. (2007) concluded that rapid recovery of ground vegetationand low N deposition counteracted nutrient leaching. At Hagfors,the vegetation recovery in all subplot treatments was very slow.The recovery increased in the order furrows, tilts, and undis-turbed soil (L. Högbom, personal communication, 2012).

After a period with unusually high precipitation, the Mn con-centration peaked in some plots at Hagfors in the late summerand autumnof 2009. In situmeasurements of thewater content inthe soil (E. Ring, personal communication, 2012) indicated that thesoil was periodically saturated, or close to saturated, during thistime. This could have changed the redox conditions in some plots,leading to more Mn in the soil solution.

In the present study, the suction cups had to be installed afterdisc trenching to allow us to position the cups under the differentsubplot treatments and avoid physical damage to the apparatusduring disc trenching. Although the first samples or sample werediscarded, the early observations could have been affected by theinstallation. A graphical examination of the results indicates thatthe TC concentration was elevated in some study plots (cf. Fig. 3).Nevertheless, all data were included in the analyses, partly be-cause no effect of installation could be detected statistically whencomparing the suction cups installed in nonscarified soil beforeand after final felling. Furthermore, when suction is applied to thesuction cups, the horizontal water flow is probably enhanced andwater from the adjacent subplot treatment could have been redi-rected to the target subplot treatment. However, given the widthsof the different subplot treatments and the central location of thecups (Fig. 1), we assume that the soil solution collected reflects theeffect of the subplot treatments to a large degree.

ConclusionsContrary to our hypothesis, the NO3

−–N concentration did notincrease with increasing N fertilization intensity despite the re-corded changes in soil chemistry (Ring et al. 2011). The N leachingrates in conjunction with fertilizer application before final fellingwould have provided valuable information, especially since theapplication intervals differed among N regimes. The harvesting oflogging residues is likely to have contributed to the low NO3

−–Nconcentrations, but how and to what degree remains unclear.Thus, the present study shows that previous N fertilization ofN-limited coniferous forest does not necessarily significantly af-fect most of the major constituents in the soil solution afterwhole-tree harvesting; however, important questions related toharvest intensity, short-term leaching, and N regime remain un-answered. Finally, the similar response to disc trenching at thetwo study sites indicates that the findings from this study could berepresentative of the effects of disc trenching at other N-limitedconifer forests located on well-drained mineral soils in the borealand hemiboreal zones.

AcknowledgementsThe authors wish to thank land owners Bergvik and Stora Enso

(Hagfors) and Sveaskog (Nissafors) for hosting the experimentsand for adapting their procedures to accommodate the experi-mental design. We wish to acknowledge the many people whohavemade this study possible, both during the course of the studyand the preceding 25 years when the experiments were estab-lished and maintained, in particular Lars-Åke Dahl, ThomasHjerpe, Hagos Lundström, Sten Nordlund, Ove Nyberg, and ToreSöderkvist. The chemical analyses were performed by the SoilScience Laboratory of the Department of Forest Ecology and Man-agement, Swedish University of Agricultural Sciences. The studywas financed by grants from The Swedish Research Council forEnvironment, Agricultural Sciences and Spatial Planning, Skog-forsk's framework program, and Future Forests, a multidisci-plinary research program supported by the Foundation forStrategic Environmental Research, the Swedish Forestry, theSwedish University of Agricultural Sciences, Umeå University, andSkogforsk.

ReferencesAber, J.D., Nadelhoffer, K.J., Steudler, P., and Melillo, J.M. 1989. Nitrogen satura-

tion in northern forest ecosystems. BioScience, 39(6): 378–386. doi:10.2307/1311067.

Alexandersson, H., and Eggertsson Karlström, C. 2001. Temperaturen och ned-erbörden i Sverige 1961–1990: Referensnormaler – utgåva 2. Swedish Meteo-rological and Hydrological Institute SMHI Meteorologi 99, Norrköping.

Baskerville, G.L. 1972. Use of logarithmic regression in the estimation of plantbiomass. Can. J. For. Res. 2(1): 49–53. doi:10.1139/x72-009.

Berdén, M., Nilsson, S.I., and Nyman, P. 1997. Ion leaching before and afterclear-cutting in a Norway spruce stand — Effects of long-term application ofammonium nitrate and superphosphate. Water Air Soil Pollut. 93(1–4): 1–26.doi:10.1023/A:1022167013669.

Futter, M.N., Ring, E., Högbom, L., Entenmann, S., and Bishop, K. 2010. Conse-quences of nitrate leaching following stem-only harvesting of Swedish for-ests are dependent on spatial scale. Environ. Pollut. 158(12): 3552–3559. doi:10.1016/j.envpol.2010.08.016.

Gundersen, P., Schmidt, I.K., and Raulund-Rasmussen, K. 2006. Leaching of ni-trate from temperate forests — Effects of air pollution and forest manage-ment. Environ. Rev. 14(1): 1–57. doi:10.1139/A05-015.

Högbom, L., and Nohrstedt, H.-Ö. 2000. Effects of re-application of nitrogenfertilizer on forest soil-water chemistry, with special reference to cadmium.Skogforsk Rep. 2.

Jacobson, S., and Pettersson, F. 2001. Growth responses following nitrogen andN–P–K–Mg additions to previously N-fertilized Scots pine and Norway sprucestands onmineral soils in Sweden. Can. J. For. Res. 31(5): 899–909. doi:10.1139/x01-020.

Jacobson, S., and Pettersson, F. 2010. An assessment of different fertilizationregimes in three boreal coniferous stands. Silva Fenn. 44(5): 815–827.

Johansson, M.-B. 1994. The influence of soil scarification on the turnover rate ofslash needles and nutrient release. Scand. J. Forest Res. 9(1–4): 170–179. doi:10.1080/02827589409382828.

Lucas, R.W., Klaminder, J., Futter, M.N., Bishop, K.H., Egnell, G., Laudon, H., and

Fig. 4. Least-squares mean concentrations of NO3−–N in soil

solution by scarification treatment at Nissafors. “×” indicates asampling occasion with a significant difference (p < 0.05) betweentreatments. Since no interaction between the N regime andscarification was detected, the means presented were calculatedusing data from both N regimes. No scarification (- – -), furrows (o),area between furrows (Œ), and tilts (Œ).

Ring et al. 403

Published by NRC Research Press

Can

. J. F

or. R

es. D

ownl

oade

d fr

om w

ww

.nrc

rese

arch

pres

s.co

m b

y U

nive

rsity

of

Wes

tern

Ont

ario

on

11/1

2/14

For

pers

onal

use

onl

y.

Högberg, P. 2011. A meta-analysis of the effects of nitrogen additions on basecations: implications for plants, soils, and streams. For. Ecol. Manage. 262(2):95–104. doi:10.1016/j.foreco.2011.03.018.

Lundmark-Thelin, A., and Johansson, M.-B. 1997. Influence of mechanical sitepreparation on decomposition and nutrient dynamics of Norway spruce (Pi-cea abies (L.) Karst.) needle litter and slash needles. For. Ecol. Manage. 96(1–2):101–110. doi:10.1016/S0378-1127(97)00040-6.

Melin, J., and Nômmik, H. 1988. Fertilizer nitrogen distribution in a Pinus sylves-tris/Picea abies ecosystem, Central Sweden. Scand. J. Forest Res. 3(1–4): 3–15.doi:10.1080/02827588809382490.

Nohrstedt, H.-Ö. 1988. Studies of soil chemistry in two forest fertilization exper-iments. The Institute for Forest Improvement Rep. 2.

Nohrstedt, H.-Ö. 1989. Phosphorus mineralization in two acid forest floors asaffected by previous nitrogen fertilization. The Institute for Forest Improve-ment Rep. 9.

Nohrstedt, H.-Ö. 1990. Effects of repeated nitrogen fertilization with differentdoses on soil properties in a Pinus sylvestris stand. Scand. J. For. Res. 5(1–4):3–15. doi:10.1080/02827589009382588.

Nohrstedt, H.-Ö. 1998. Residual effects of N fertilization on soil–water chemistryand ground vegetation in a Swedish Scots pine forest. Environ. Pollut. 102(1):77–83. doi:10.1016/S0269-7491(98)80018-3.

Nohrstedt, H.-Ö., Ring, E., Klemedtsson, L., and Nilsson, Å. 1994. Nitrogen lossesand soil water acidity after clear-felling of fertilized experimental plots in aPinus sylvestris stand. For. Ecol. Manage. 66(1–3): 69–86. doi:10.1016/0378-1127(94)90149-X.

Palviainen, M., Finér, L., Laurén, A., Mannerkoski, H., Piirainen, S., and Starr, M.2007. Development of ground vegetation biomass and nutrient pools in aclear-cut disc-plowed boreal forest. Plant Soil, 297(1–2): 43–52. doi:10.1007/s11104-007-9317-2.

Pettersson, F. 1994. Predictive functions for calculating the total response ingrowth to nitrogen fertilization, duration and distribution over time. Skog-forsk Rep. 4.

Piirainen, S., Finér, L., Mannerkoski, H., and Starr, M. 2007. Carbon, nitrogenand phosphorus leaching after site preparation at a boreal forest clear-cutarea. For. Ecol. Manage. 243(1): 10–18. doi:10.1016/j.foreco.2007.01.053.

Ring, E. 1996. Effects of previous N fertilizations on soil–water pH and N concen-trations after clear-felling and soil scarification at a Pinus sylvestris site. Scand.J. Forest Res. 11(1–4): 7–16. doi:10.1080/02827589609382907.

Ring, E., Högbom, L., and Nohrstedt, H.-Ö. 2001. Effects of brash removal afterclear felling on soil and soil-solution chemistry and field-layer biomass in anexperimental nitrogen gradient. In Optimizing nitrogen management infood and energy production and environmental protection. Proceedings ofthe 2nd International Nitrogen Conference on Science and Policy. Anony-mous. The ScientificWorld. pp. 457–466.

Ring, E., Bergholm, J., Olsson, B.A., and Jansson, G. 2003. Urea fertilizations of aNorway spruce stand: effects on nitrogen in soil water and field-layer vege-tation after final felling. Can. J. For. Res. 33(2): 375–384. doi:10.1139/X02-187.

Ring, E., Jacobson, J., and Nohrstedt, H.-Ö. 2006. Soil-solution chemistry in aconiferous stand after adding wood ash and nitrogen. Can. J. For. Res. 36(1):153–163. doi:10.1139/X05-242.

Ring, E., Jacobson, S., and Högbom, L. 2011. Long-term effects of nitrogen fertil-ization on soil chemistry in three Scots pine stands in Sweden. Can. J. For.Res. 41(2): 279–288. doi:10.1139/X10-208.

Smolander, A., Paavolainen, L., and Mälkönen, E. 2000. C and N transformationsin forest soil after mounding for regeneration. For. Ecol. Manage. 134(1–3):17–28. doi:10.1016/S0378-1127(99)00242-X.

Staaf, H., and Olsson, B.A. 1994. Effects of slash removal and stump harvestingon soil water chemistry in a clearcutting in SW Sweden. Scand. J. Forest Res.9(1–4): 305–310. doi:10.1080/02827589409382844.

Swedish Forest Agency. 2012. Swedish statistical yearbook of forestry. SwedishForest Agency, Jönköping, Sweden.

Tamm, C.O., and Popovi=c, B. 1974. Intensive fertilization with nitrogen as astressing factor in a spruce ecosystem. 1. Soil effects. Studia Forestalia Suecica121.

Tamm, C.O., Holmen, H., Popovíc, B., and Wiklander, G. 1974. Leaching of plantnutrients from soils as a consequence of forestry operations. Ambio, 3: 211–221.

Tanskanen, N., and Ilvesniemi, H. 2007. Spatial distribution of fine roots atploughed Norway spruce forest sites. Silva Fenn. 41: 45–54.

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