Effects of strip wise tillage in combination with liming on chemical and physical properties of acidic spruce forest soils after clear cutting

Forest Ecology and Management 180 (2003) 75–83

Effects of strip wise tillage in combination with liming on chemical and physical properties of acidic spruce forest soils after clear cutting V. Geissena,*, R.-Y. Kimb, A. Scho¨ningb, St. Schu¨ttec, G.W. Bru¨mmerb a

El Colegio de la Frontera Sur, Administracion de Correos No. 2, Atasta, Apartado Postal 1042, C.P. 86168, Villahermosa, Tabasco, Mexico b Department of Soil Science, Nussallee 13, 53115 Bonn, Germany c Forstamt Kottenforst, Flerzheimer Allee 121, 53123 Bonn, Germany

Received 12 December 2001; received in revised form 14 August 2002; accepted 1 November 2002 In commemoration of Dr. Hans Gewehr

Abstract We investigated the initial effects of strip wise soil loosening (0–35 cm depth) on soil chemical and physical parameters by using a deeply working rotary cultivator in combination with liming and mixing of the dolomite with the soil material of acidic forests. The investigations took place 8 months after the treatment. pH values and contents of exchangeable Ca and Mg increased significantly at the tilled depth whereas the content of exchangeable Al and easily soluble P decreased. The rate of mineralisation increased at this depth which was shown by a loss of Corg, Ntot and short-term loss of NO3-N. The treatment led to a mobilisation of Mn at the tilled depth. However, the content of exchangeable Pb decreased due to an increased pH value. Below the tillage depth of 35 cm only partly significant changes of exchangeable Mn and NO3-N were found. The total porosity and bulk density at 10–15 and 40–45 cm depths were not significantly different from those in the control plot, but the rate of infiltration increased significantly. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Forest soil; Liming; Nitrate; Strip wise tillage; Soil properties

1. Introduction About 78% of Germany’s forest soils are strongly to extremely acidic with pH values below 4.2 (Veerhoff et al., 1996). Acidic forest soils are characterised by a low supply in exchangeable basic nutrient cations such as Ca and Mg whereas increasing concentrations of exchangeable heavy metals and aluminium are found * Corresponding author. Tel./fax: þ52-993-3511861. E-mail address: [email protected] (V. Geissen).

(Ulrich, 1981; Abrahamsen, 1984; Geissen et al., 1999). The toxic effects of exchangeable aluminium and heavy metals on trees and the edaphon are well known (Kandeler et al., 1996; Veerhoff et al., 1996). In acidic forest soil the biological activity is also strongly reduced (Geissen and Bru¨mmer, 1999). As a consequence, organic layers with partly undecomposed litter are found on mineral soil. Highly acidic soils require countermeasures such as liming. In the past 10–15 years the surfaces of many forest soils in Germany were limed with dolomite. The

0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(02)00601-1

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effects of these treatments on soil chemical parameters have been described by several authors (e.g. Kreutzer et al., 1991; Scho¨ ning et al., 1997; Geissen et al., 1999). They conclude that the effects on the organic layers are mainly positive, i.e. increasing pH, increasing contents of Ca and Mg and reduced contents of exchangeable Al and heavy metals. On the other hand liming often induces a higher mineralisation and consequently increases the danger of leaching of nitrate or heavy metals (Geissen, 2000; Nilsson et al., 2001). Depending on the thickness of the organic layer the applied dolomite leaches with a delay of several years into deeper layers of the mineral soil (Wenzel, 1989; Marschner, 1990; Arnold and van Diest, 1993; Geissen et al., 1999). Furthermore, the lime applied is often neutralised in the organic layer even before it reaches mineral soil horizons. This phenomenon is particularly prevalent in spruce forests with thick organic horizons (Kreutzer et al., 1991). Another severe problem in forest soils is compaction which is often caused by the use of heavy machinery. This strongly reduces infiltration and leaching rate and also root growth (Schulte-Karring, 1992). The discussion on how to solve the problems of acidification and compaction is very controversial (Benecke, 1992; Horn and Lebert, 1992). Some authors favour cultivation to loosen compact, acidic soils in combination with liming to improve soil structure and pH in deeper layers (Schulte-Karring, 1992; Schu¨ ler, 1994). Other authors take the opposite view and favour a preservation of the natural soil profile. Since 1990 different methods of melioration have been developed (Schneider et al., 1997). All these methods are based on a deep loosening of soils in combination with liming and mixing of the dolomite with the soil material. At the same time the organic layers are worked into the mineral soil. These treatments are proposed for deforested areas. However, the kind and intensity of melioration treatments differ considerably. Schulte-Karring (1992) proposes to till and loosen the whole surface area, Schu¨ ler (1994) suggested a strip wise tillage so as to reduce negative effects such as leaching of nitrate, Al and heavy metals as well as mineralisation of organic carbon. Furthermore, in the case of strip wise tillage the organic layer as the main habitat of soil fauna and flora is only partly destroyed. The negative effects are often very strong in the initial phase, that means in the first year following

the treatment. Therefore, this study concentrates on the initial effects of strip wise tillage in combination with liming and mixing of the dolomite with the soil material on soil chemical and physical properties of acidic and partly compact Stagnic Alisols.

2. Material and methods 2.1. Experimental site The study was conducted in the Kottenforst near Bonn (West-Germany). The test site is located on a plain, about 160 m a.s.l. Stagnic Alisols are typical soil types. The parent material is loess over terrace material of the Rhine river. According to the German classification system these soils are called ‘‘Pseudogley’’ with following horizons: L (7–5 cm), Of (5– 3 cm), Oh (3–0 cm), Ah (0–1 cm), Aeh (1–7 cm), Sew (7–17 cm), Sw (17–80 cm), Sd (>80 cm). The typical humus form is rawhumus like moder (Rohhumusartiger Moder) (AG Boden, 1994). The 80 years old spruce forest on this site was limed in 1988 by helicopter with 3 t ha1 dolomite. In January 1996 clear felling of the forest was carried out. 2.2. Treatment In October 1996 a strip wise tillage of the site with a rotary cultivator was carried out (cf. Schu¨ ler, 1994) and liming with 23 t ha1 dolomite in the strips, which corresponds to 3 t ha1 dolomite for the whole area. The strips were 30 cm wide and they were cultivated to a depth of 35–40 cm. The dolomite was mixed with the soil material within this depth using the rotary cultivator. An area of 2 m between the strips was left untreated. Therefore, only 13% of the total area was cultivated. In April/May 1997 deciduous trees were planted on the prepared strips. 2.3. Sampling and soil analysis In June 1997, after the planting of deciduous trees, soil samples were taken for the analysis of chemical parameters in two tilled strips (S1, S2) and in the untreated area between them (control strip C). In total we took 48 soil cores for chemical analysis with a split tube sampler (5 cm diameter) at depths of up to 1 m,

V. Geissen et al. / Forest Ecology and Management 180 (2003) 75–83 Table 1 Soil parameters and analytical methods Parameter

Methods

pH Corg, Ntot NO3

0.01 M CaCl2 CNS-Analyser Extraction with 0.01 M CaCl2 (Houba et al., 1986) Extraction with 1 M NH4NO3 (Zeien and Bru¨ mmer, 1991) Extraction with 0.5 M NH4Cl (Tru¨ by and Aldinger, 1989) Tru¨ by and Aldinger (1989) Extraction with aqua regina

NH4NO3-extractable fraction (Mn, Pb) NH4Cl-extractable fraction (Ca, Mg, Al, P) CECe Total content (Ca, Mg, P, Al, Mn, Pb) Density, porosity

Hartge and Horn (1992)

i.e. 16 individual cores per strip. We divided them into different depths of 0–10, 10–20, 20–35, 35–50, 50–75 and 75–100 cm. Four samples of each depth were combined to form one mixed sample so that we received four mixed samples per depth and strip, i.e. 72 mixed samples in total. Then the following parameters were measured: pH(CaCl2) value, content of Corg and Ntot, content of the exchangeable fraction and total content of Ca, Mg, P, Al, Mn and Pb (Table 1). Due to favourable soil moisture conditions we took the samples for soil physical analysis in October 1997.

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Eight soil sample rings (100 cm3) were inserted at two soil depths (10–15, 40–45 cm) in each of the two tilled strips and in the untreated control strip. We analysed the density and porosity of the samples (Table 1). In addition to that the infiltration rate at a depth of 10 cm was measured using a double ring infiltrometer. This measurement was carried out with four replications. 2.4. Statistics We used ANOVA followed by the multiple t-test to find out significant differences between the soil parameters of the tilled and the control strips on a significance level of P < 0:05. We calculated the losses of Corg, Ntot and NO3-N in the meliorated strips by taking the differences of the C and N contents between the control and the treated strips.

3. Results 3.1. Soil chemical parameters Soil tillage in combination with liming led to significant increases of the pH(CaCl2) values in the upper 35 cm of the soil (Fig. 1a). At the same time the Al

Fig. 1. pH(CaCl2) (a) and Al proportion (%) (b) of the effective CEC (b) in the tilled and limed strips (S1, S2) and the control strip (C) at different soil depths (tilled depth: 35 cm); significant differences between the strips (P < 0:05): a < b.

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proportions of the exchangeable cations were significantly reduced from an average of 88 to 35% (Fig. 1b). The mineral soil of the untreated control strip C was highly acidic with pH values of <4.0, whereas pH values in the tilled strips (S1, S2) were between 4 and 5. In S1 the pH values exceeded the critical value of 4.5 for mobilisation of Al (Geissen et al., 1999) down to a depth of 35 cm and in S2 down to a depth of 10 cm. Below the tilled strata no significant differences between the control strip and the cultivated strips were observed (Fig. 1a and b). The effective cation exchange capacity increased in the treated depth of S1 and S2. However, the values remained smaller than 10 mmolc kg1 and the effect was not significant due to the fact that the increase of the variable charge between pH 4 and 5 is only small. The amount of NH4Cl-extractable supply of Ca and Mg increased significantly at a depth of 0–35 cm in the strips S1 and S2 (Table 2). The Ca supply in this zone can be characterised as medium/high and the Mg supply as high (AK Standortskartierung, 1996) whereas the Ca and Mg supply in the control strip was low even after including the contents in the organic layers in the calculation. However, liming led to a reduction of available P. Consequently, the supply of plant available P in the root zone of the tilled strips S1 and S2 was significantly lower than in the untreated control strip (Table 2). We also investigated the Corg and Ntot losses in the loosened strips compared to the untreated control area. Table 2 Supply of NH4Cl-extractable Ca, Mg and P (kg ha1) in the tilled strips (S1, S2) and the control strip (C) in top soil (0–35 cm); significant differences between the strips (P < 0:05): a < b < c Strip

Ca

Mg

P

S1 x s

3204 b 698

1358 b 289

3.8 a 0.5

S2 x s

2386 b 624

1020 b 292

3.9 a 0.5

C without Of, Oh x s

403 a 24

213 a 17

5.4 b 0.1

C including Of, Oh x s

494 a 26

237 a 18

10.7 c 1.1

We observed Corg losses in the loosened zone of S1 and S2 of 36 and 34 t ha1 and Ntot losses of 2.1 t ha1 (Table 3). Furthermore, the content of NO3-N was significantly lower (12.9 kg ha1 (S1) and 12.8 kg ha1) in the loosened zone of the treated strips S1 and S2 than in the control strip. However, only 13% of the whole area were treated. Therefore, the losses referred to the whole area were only 4.7 (4.4) t ha1 Corg and 0.27 t ha1 Ntot. At a depth below 35 cm there were no significant differences of Corg and Ntot between the control strip and the treated strips. However, we observed in S1 a significantly higher content of NO3-N at a depth of 75–100 cm as compared to the control strip C. Also in S2 the content of NO3-N was higher at this depth, but the difference was not significant. The total content of Mn was very high in the organic layers of the untreated control strip (Fig. 2a). Since the mobility of Mn increases already at pH < 5:7 (Hornburg and Bru¨ mmer, 1993) the content of exchangeable Mn was also very high in these layers with values of 508 mg kg1 (Of) and 271 mg kg1 (Oh) (Fig. 2b). The treatment only induced significant increase in total Mn contents in the layer of 0–10 cm in S1 and S2. At the other depths the total Mn content showed a very heterogenious picture. In both treated strips, the content of exchangeable Mn significantly increased at a depth of 20–35 cm. In S1 the content of exchangeable Mn was also significantly higher at a depth of 75–100 cm. As previously described a significantly higher content of NO3-N was also observed at the depth of 75–100 cm. The content of total Pb exceeded the precautionary value for Pb in loamy soils of 70 mg kg1 (Federal Soil Protection and Contaminated Sites Ordinance (BBodSCHV), 1999) only in the organic layers and in the depth of 0–10 cm in the control strip (Fig. 3a). A mixing of the Pb enriched organic layers with the mineral soil also led to an enrichment of total Pb across the whole tilled depth. However, in the treated strips S1 and S2 the content of Pb did not exceed the precautionary values. In the tilled strips S1 and S2 the content of exchangeable Pb was significantly lower than in the control strip, especially at a depth of 0–10 cm (Fig. 3b). While the trigger value for exchangeable Pb of 3.5 mg kg1 (Soil Protection Act, 1993) was exceeded at the 0–10 cm depth of the control strip, it was not exceeded in the tilled strips.

Corg (t ha1) S1 Of Oh 0–10 cm 10–20 cm 20–35 cm P 035 cm Loss in the treated strips (13% of the whole area) in a depth of 0–35 cm Loss referred to the whole area in a depth of 0–35 cm 35–50 cm 50–75 cm 75–100 cm P 35100 cm Loss in the treated strips (13% of the whole area) in a depth of 35–100 cm a

Ntot (t ha1)

S2

35.8 a 27.1 b 44.4 b

33.0 a 27.2 b 49.1 b

107 a

109 a

36

34

C 14.7 51.5 56.0 b 11.9 a 8.5 a 143 b

S1

NO3-N (kg ha1)

S2

C

1.5 a 1.1 b 1.8 b

1.4 a 1.1 b 1.9 b

0.6 2.5 2.2 b 0.5 a 0.7 a

4.4 a

4.4 a

6.5 b

S1

S2

2.1 a 2.2 a 2.7 a

2.5 a 2.0 a 2.6 a

2.0 3.4 6.5 b 3.5 b 4.5 b

7.0 a

7.1 a

19.9 b

2.1

2.1

12.9

12.8

0.27

0.27

1.7

1.7

4.7

4.4

6.7 8.7 10.2

8.1 11.0 9.2

5.6 12.1 9.3

0.6 0.9 1.2

0.5 1.5 0.8

0.4 1.3 0.8

3.6 5.4 6.9 b

25.6

28.3

27.0

2.7

2.8

2.5

15.9 b

Ns

a

NS

C

NS

NS

þ9.0

3.9 5.4 4.9 a 14.2 NS

3.5 4.4 4.7 a 12.6 a

V. Geissen et al. / Forest Ecology and Management 180 (2003) 75–83

Table 3 Supply of Corg, Ntot (t ha1) and NO3-N (kg ha1) in the top soil (0–35 cm) and the subsoil (35–100 cm) of the tilled and limed strips (S1, S2) and the control strip (C) as well as the calculated losses of Corg, Ntot and NO3-N in S1 and S2 in comparison with the control strip (values of losses referring to the strips (13% of the total area) and calculated for the total area); significant differences between S1, S2 and C (P < 0:05): a < b

Not significant.

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Fig. 2. Contents of total Mn (a) and NH4NO3-extractable Mn (b) (mg kg1) in the tilled and limed strips (S1, S2) and the untreated control strip (C) at different soil depths (tilled depth: 35 cm); significant differences between the strips (P < 0:05): a < b.

3.2. Soil physical parameters Eight months after the treatment no obvious influence of soil tillage could be observed on total soil porosity and soil density, neither at the tilled depth nor

below (Fig. 4a and b). However, the infiltration rate at a soil depth of 10 cm was significantly higher in the tilled strips than in the control strip (Fig. 5). Moreover, it has to be pointed out that the treatment did not lead to compaction in the layer just below the loosened depth.

Fig. 3. Contents of total Pb (a) and NH4NO3-extractable Pb (b) (mg kg1) in the tilled and limed strips (S1, S2) and the untreated control strip (C) at different soil depths (tilled depth: 35 cm); significant differences between the strips (P < 0:05): a < b.

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Fig. 4. Porosity (%) (a) and density (g cm3) (b) in the tilled and limed strips (S1, S2) and the control strip (C) at two soil depths (10–15, 40– 45 cm); significant differences between the strips (P < 0:05): a < b.

Fig. 5. Infiltration rate in the tilled and limed strips (S1, S2) and the control strip (C) at a depth of 10 cm; significant differences between the strips (P < 0:05): a < b.

4. Discussion The positive effects of liming, loosening and mixing the upper 35 cm of acidic forest soils are an increase of pH, exchangeable Ca and Mg and a decrease of exchangeable Al in the tilled depth. However, also negative ecological effects of the treatments must be considered. According to our data the treatment obviously induced a high mineralisation of organic material, which led to high losses of organic carbon and total nitrogen. Increased mineralisation rates after cultivation of forest soils are also described by Makeschin (1985), Schu¨ ler (1992) and Smolander et al. (2000). The process of mineralisation was sped up by the combination of soil tillage, mixing and liming, which led to an increase in microbial activity. Dolomite application on the soil surface also increases the mineralisation rate (Wiedey, 1991; Geissen et al., 1999; Nilsson et al., 2001). However, the rate is much lower than in cases where liming is combined with a loosening of the mineral soil. Schu¨ ler (1992) and Balcar (1993) also observed extremely high losses of Corg and Ntot after cultivation. However, it has to be pointed out that in our

study only 13% of the whole area was tilled so the losses only occur in the tilled area and are not spread over the whole area. The Corg and Ntot losses calculated for the whole area (treated and untreated) were only 4.7 and 4.4 t ha1 Corg and 0.27 t ha1 Ntot. The ecological problems arising from increased mineralisation have been discussed by several authors (e.g. Schu¨ ler, 1994; Nilsson et al., 2001). The organic C and total N supply can decrease because of plant uptake, leaching processes or gaseous escape (Ballard, 2000). These processes can explain the decrease of NO3-N in the loosened area. Gaseous escape is often observed under humid soil conditions. In acidic forest soils the gaseous form of N is mainly N2O. Escapes of N2O can contribute to global climatic changes. As a significant increase in NO3-N was only observed in the subsoil of one of the tilled strips (S1, Table 3) besides leaching also other processes may be responsible for the calculated N losses. In the redoximorphic soils referred to our study we also consider denitrification and gaseous N2O escapes to be important processes for the observed N losses. However, it is difficult to calculate the proportion of NO3-N taken up by plants and the amount lost by gaseous escape or leaching. Furthermore it has to be pointed out that the observed contents of NO3-N represent short-term observations and further investigations are needed to obtain findings on long-term effects. The increase of NO3-N in the subsoil may be affected by leaching of NO3-N, which can lead to an accumulation in the subsoil as well as in ground water. The treatment led to a decreased content of exchangeable P. The P immobilisation caused by liming has also been described by several other

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authors (e.g. Kreutzer et al., 1991). Most likely it is caused by P occlusion as also observed by Geissen et al. (1999). To overcome this problem we suggest the application of rock phosphate together with dolomite in P deficient soils. The treatment led to increased total contents of Mn and Pb in the tilled and limed strips (Figs. 3a and 4a). Mixing the Mn and Pb rich organic layers with the mineral soil caused this increase. The differences in the total content of Mn in the strips S1 and S2 may be caused by different amounts of Mn concretions which are characteristics of Stagnic Alisols. The exchangeable content of Mn increased in the deeper layers of the treated strips, whereas the exchangeable Pb content decreased in the limed and mixed upper layers. The increase of exchangeable Mn can possibly be put down to an increased total Mn content but can also be attributed to mobilisation and leaching processes triggered off by the treatments. The mobilisation of Mn already starts at pH values of < 5.7, (Hornburg and Bru¨ mmer, 1993). Consequently, the very acidic soil conditions under investigation in our study reveal that pH value was not most important for mobilisation or immobilisation processes of Mn. We assume that mineralisation led to an increased amount of organic acids, which probably caused the mobilisation, and leaching of Mn. This heavy metal mobilisation was also observed by McBride (1989). In contrast to Mn, the exchangeable content of Pb decreased in the tilled strips. This can be attributed to the effect of liming which led to pH values > 4. The mobilisation of Pb strongly depends on soil acidity. The critical pH(CaCl2) value for Pb mobilisation is known to be 3.5 (Hornburg and Bru¨ mmer, 1993). Even though there was an increase in the total content this fact was overweighed by a fixation of Pb due to an increase in the pH value. We observed contradicting results with respect to soil physical parameters. Whereas porosity and bulk density were not influenced by the treatments the infiltration rate significantly increased. This contradiction can be explained by the methods used. Soil porosity and density were mainly investigated in soil aggregates, whereas the investigations of infiltration rates also included the macropores between the aggregates (Hartge and Horn, 1992). Schneider et al. (1997) also observed a significant increase in macropores after tillage with a rotary cultivator.

This study shows the initial short-term effects of strip wise tillage and liming in forest soils. These are the conditions under which trees are planted and start to grow. Further investigations are necessary to obtain information on long-term effects.

5. Conclusions In the initial phase after loosening, liming and mixing of forest soils, i.e. in the first year after the treatment the strongest effects on soil chemical and physical properties occur despite the fact that the process of dissolution of lime is not yet completed. The potential ecological risks such as leaching of heavy metals and nitrate are especially high during this phase because of a highly increased mineralisation rate. The results of our study show that even though the rate of mineralisation strongly increased, the positive effects of the treatment such as increased pH and supply in basic nutrients cations and decreased contents of exchangeable Pb and Al in the treated strips overweighed the negative effects such as loss of C and N and mobilisation of Mn. Leaching of nitrate and Mn into deeper layers was low. Therefore the risk of ground water contamination is small. Furthermore, strip wise tillage reduces the negative effects only to 13% of the whole surface area. Taking into consideration all positive and negative effects of the treatment we recommend the described treatment for acidic forest soils after clear felling. In the treated strips the improved initial soil conditions for the planted trees will probably lead to an advanced growing.

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