Soil erosion and changes in the physical properties of Lithuanian ...

Acta Agriculturae Scandinavica Section B
Soil and Plant Science, 2008; 58: 66
76

ORIGINAL ARTICLE

Soil erosion and changes in the physical properties of Lithuanian Eutric Albeluvisols under different land use systems

˙ 1 & M.A. FULLEN2 B. JANKAUSKAS1, G. JANKAUSKIENE 1

Kaltine˙nai Research Station of the Lithuanian Institute of Agriculture, Varniu˛, Lithuania, and 2School of Applied Sciences, The University of Wolverhampton, Wolverhampton, UK

Abstract The investigations aimed to: 1) evaluate water erosion rates on undulating slopes in Lithuania under different land use systems; 2) study changes in soil physical properties on the differently eroded slopes; and 3) better understand relationships between soil physical properties and soil erodibility. Research data were obtained on loamy sand and clay loam Eutric Albeluvisols located on the undulating hilly relief of the Zˇemaicˇiai Uplands of Western Lithuania. The results of 18 years of water erosion investigations under different land use systems on slopes of varying steepness are presented. Attention is focused on changes in soil physical properties in relation to soil erosion severity. Measured water erosion rates in the field experiments were: 3.2
8.6 m3 ha 1 yr 1 under winter rye, 9.0
27.1 m3 ha 1 yr 1 under spring barley and 24.2
87.1 m3 ha 1 yr 1 under potatoes. Perennial grasses completely prevented water erosion, while erosion-preventive grass-grain crop rotations (67% grasses, 33% cereal grains) decreased soil losses by 75
80% compared to the field crop rotation, containing 17% tillage crops (potatoes), 33% grasses and 50% cereal grains. The grain-grass crop rotation (33% grasses and 67% cereal grains) decreased soil erosion rates by 23
24%. The percentage of clay-silt and clay fractions of arable soil horizons increased, while the total soil porosity and moisture retention capacity decreased with increased soil erosion. Phytocenoses, including sod-forming perennial grasses and grass-grain crop rotations, led to changes in the physical properties of eroded soils; soil bulk density decreased and percentage total porosity and moisture retention capacity increased. The grass-grain crop rotations increased the water-stable soil structure (measured as water-stable soil aggregates) by 11.03 per cent units and sod-forming perennial grasses increased aggregate stability by 9.86 per cent units compared with the grain-grass crop rotation on the 10
148 slope. Therefore, grass-grain crop rotations and sod-forming perennial grasses decreased soil erodibility and thus could assist both erosion control and the ecological stability of the vulnerable hilly-undulating landscape.

Keywords: Aggregate strength, bulk density, moisture retention capacity, soil texture, total porosity, undulating upland topography, water erosion rates.

Introduction Soil erosion is one of the world’s most serious environmental problems, causing extensive loss of cultivated and potentially productive soil and crop yields (Fullen & Catt, 2004; Morgan, 1995; Skoien, 1995). Highly eroded soils tend to have reduced productivity, degraded structure and lower organic matter contents and are poor environments for root growth (Frye et al., 1982; Lindstrom et al., 1994). Water erosion is the main soil degradation process in agricultural areas, that endangers 56% of global arable land and has already eliminated an estimated

430 million hectares from agricultural production, or 30% of total available arable land (Djorovic, 1999). About 1028 million hectares of global soils were moderately to excessively affected by water and wind erosion (Griesbach & Sanders, 1998). The limited availability of soil resources for food production and renewable biotic resources, caused by steady population growth and accelerated soil degradation, may have greater negative impacts on global living conditions than the human-induced greenhouse effect (Eger et al., 1998). Soil erosion is not always due to hostile climates, but can result from

Correspondence: B. Jankauskas, Kaltine˙nai Research Station of the Lithuanian Institute of Agriculture, Varniu˛ 17, LT-75451 Kaltine˙nai, Sˇilale˙ District, Lithuania. Fax: 370 449 57141. E-mail: [email protected]

(Received 10 May 2006; accepted 10 January 2007) ISSN 0906-4710 print/ISSN 1651-1913 online # 2008 Taylor & Francis DOI: 10.1080/09064710701214379

Lithuanian Albeluvisols under different management systems land mismanagement and inappropriate policies (Boardman et al., 2003; Fullen, 2003). For example, erosion on UK agricultural land has increased over the last 20 years, with no evidence of significant climatic changes (Boardman, 1992). Soil erosion has considerably worsened in Swaziland over the last 20 years (Morgan et al., 1997). During the last 50 years, erosion has increased about 30-fold in Russia and associated crop production has decreased by 50
60% (Andronikov, 2000). Annual erosion rates on cultivated land vary from 0.1 to 20 Mg ha1 in the UK to 150
200 Mg ha1 in China (Morgan, 1995). Average values of soil erosion rates over large areas are, for both practical and theoretical reasons, to be treated cautiously. The rate of erosion in Europe of 17 Mg ha 1 yr1 or 10 25 Mg ha1 yr1, quoted by several authors, was based on misinterpretation and uncritical use of original field data (Boardman, 1998). Agroecosystems play a key role in promoting biodiversity (Vandermeer et al., 1998); therefore, multi-species agro-ecosystems (sod-forming long term perennial grasses and grass-grain crop rotations) are potential components for both soil conservation and biodiversity strategies. Furthermore, the global dataset of soil erodibility values shows much unexplained variance and a contributory factor is often the limited measurement period (Torri et al., 1997). Therefore, long-term studies are essential to validate potential soil conservation techniques. About 17% of Lithuania’s agricultural land is eroded, increasing to 43
58% in the hilly-undulating regions. Water erosion occurs mostly on arable slopes, as natural vegetation (woods, shrubs and grassland) effectively protects soil from erosion (Jankauskas, 1996). Wind erosion occurs on sandy arable soils mostly near the Baltic coast. Soil erosion severity on the uplands of western Lithuania is due to the combined action of natural (geological) and accelerated soil erosion. Soil erosion rates increased with slope steepness and so natural soil fertility (measured in terms of spring barley yield) decreased by 22, 40 and 62% on slopes of 2
58, 5
108 and 10
148, respectively (Jankauskas & Fullen, 2002). These results demonstrate the need for soil conservation measures on arable land in Lithuania. Therefore, the main aims of these investigations were to: 1) evaluate long-term water erosion rates on the undulating slopes in Lithuania under different land use systems; 2) study changes of soil physical properties on the differently eroded slopes and to understand relationships between physical soil properties and soil erodibility; and 3) evaluate the potential for soil conservation on eroded undulating land. Results from the first and second crop rota-

67

tions (1983
1994) were reported by Jankauskas and Jankauskiene (2003) and this paper presents soil erosion data from three crop rotations (1983
2000).

Materials and methods Study sites Research data were obtained during 1983
2000 from the Kaltine˙nai Research Station of the Lithuanian Institute of Agriculture (KRS of LIA), ˇ emaicˇiai which is located on the southern-central Z Uplands (55834?N, 22829?E). Study sites A, B and C (Figure 1) are on slopes of 2
58, 5
108 and 10
148, respectively. Field trial plot width was 3.6 m and length was 90 m on sites A and C (slopes 2
58 and 10
148) and 40 m on site B (slope 5
108). The narrow plot width was to facilitate mechanical cultivation and sowing in one tractor pass. There were four (trials A and B) or three (trial C) replications of each treatment. These experiments are part of the ‘Core Research Programme of the Global Change and Terrestrial Ecosystem (GCTE) Project’ (GCTE Report, 1997), a component of the ‘International Geosphere Biosphere Programme (IGBP)’. Field experiments were performed on eroded Eutric Albeluvisol sandy loams (FAO-UNESCO, 1994). Soil was differentially eroded along the slopes, being slightly eroded on 2
58 slopes, moderately eroded on 5
108 slopes and strongly eroded on 10
148 slopes, with colluvial deposits on basal slopes. Soil erosion was mainly caused by tillage and water erosion under continuous intensive cropping. The agrochemical properties of Ap horizons (0
20 cm) before field experiments shows topsoils were slightly acidic (pHKCl 5.3
5.8, hydrolytic acidity 94
119 cmol()kg 1), P-deficient (available P 18.3
49.8 mg kg 1), medium rich in K (available K 127.0
146.1 mg kg 1) and contained varying soil organic matter (SOM) contents. The highest percentage SOM was on less eroded 2
58 slopes (2.85%) and lowest on 10
148 slopes (2.08%). For historical reasons, soil analytical techniques were mainly former Soviet procedures (Jankauskas & Fullen, 2002). Therefore analytical results differ from those generated by currently internationally accepted protocols (e.g., USDA), but are consistent with former Soviet protocols (Jankauskas & Jankauskiene, 2003). Currently, efforts are underway to develop transfer functions between Soviet and international systems, and initial results were reported by Booth et al. (2003). Mean annual precipitation in Lithuania is ˇ emaicˇiai 626 mm, with
858 mm on the central Z Uplands and 750
800 mm on the upland fringe.

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B. Jankauskas et al.

Figure 1. Location of the Zˇemaicˇiai Uplands and the long-term field experiments (A, B and C) in Lithuania.

Annual precipitation during the study period was 635
1075 mm. Plots were deep-ploughed, usually in September, and soil was bare up to spring. Total run-off and erosion from the bare soil was measured before the following spring cultivation (usually in mid-April). Plot run-off and erosion were measured regularly after sowing, up to weekly during erosive rains. Measurements were taken from spring sowing (typically late April or early May) to mid-June for cereals and late August for potatoes. General methodological framework Long-term field experimental data were collected on slopes of 2
58, 5
108 and 10
148 since 1983. Four six-course crop rotations were compared. The annual crops are sequentially numbered (1
6). The specific rotations are: a. The field crop rotation, containing 17% tillage crops (potatoes), 33% grasses and 50% cereal grains: 1: winter rye (Secale cereale L.), 2:

potatoes (Solanum tuberosum L.), 3
4: spring barley, 5
6: clover-timothy (CT) mixture (Trifolium pratense L.-Phelum pratense L.). b. The grain-grass crop rotation, containing 33% grasses and 67% cereal grains: 1: winter rye, 2
4: spring barley, 5
6: CT. c. The grass-grain I crop rotation, containing 67% grasses and 33% cereal grains: 1: winter rye, 2: spring barley, 3
6: CT. d. The grass-grain II crop rotation, containing 67% grasses and 33% cereal grains: 1 winter rye, 2: spring barley, 3
6: mixture of orchard grass-red fescue (OF) (Dactylis glomerata L.-Festuca rubra L.). A multi-species mixture of perennial grasses for long-term use which contribute to soil humus formation (sod-forming grasses: g) were grown on 10
148 slopes. The mixture replaced the field crop rotation, as tillage crops are not recommended in Lithuania on slopes 108 (Jankauskas, 1996). The grass mixture consisted of 20% each of common

Lithuanian Albeluvisols under different management systems

69

timothy, red fescue, white clover (Trifolium repens L.), Kentucky bluegrass (Poa pratensis L.) and birdsfoot trefoil (Lotus corniculatus L).

where sx1 ; sx2 ; sxn are individual errors of a single (one year) investigation and n is the number of investigations.

Soil management

Sampling and analytical methods

Soil management and fertilizer treatments were applied in accordance with measured soil properties and standard regional agricultural practice. Before field experiments, soils were limed with one CaCO3 application (according to hydrolytic acidity). Subsequent liming before each crop rotation enabled pH standardization on all investigated slopes. Chemical fertilizer inputs (ammonium nitrate, granulated superphosphate and potassium chloride) were used according to plant requirements and soil properties. Mean annual applications of mineral fertilizers were: N60P28.4K66 (field crops), N50P26.2K58 (grain-grass crops), N70P26.2K66 (grass-grain I crops) and N120P26.2K66 (grass-grain II crops).

Soils were sampled before field experiments commenced in autumn 1981 and after every six years (i.e., after each full crop rotation). Representative soil samples (0
20 cm depth) for chemical soil analysis were taken from each field plot using an auger. Some 10
13 samples were taken from each plot, depending on the number of plot replications (10 samples where there were four replications and 13 where there were three replications). The individual samples from three or four replications were combined to form one representative treatment sample. For historical reasons, chemical and some physical soil analytical techniques were mainly former Soviet procedures. Soil reaction (pHKCl) was determined in 1 M KCl soil sample extracts using a calibrated digital pH meter. Hydrolytic acidity was determined in 1 M CH3COONa and soil sample extract (ratio sample:extract, 1:25 for mineral soil) by titrating with 1 M NaOH (Askinazi, 1975). Exchangeable bases were determined by the Kappen-Hilkovic method, which involves hot titration of 0.1 M HCl and soil sample filtrate (ratio sample:extract 1:5) with 0.1 M NaOH (Askinazi, 1975). Ca , Mg  , K, Na  and NH4 concentrations were determined on filtrates. Available P and K were extracted with ammonium acetate-lactate (A-L solution pH 3.7; ratio 1:20). Available P was determined by spectrophotometer and K determined by flame photometry (Egner et al., 1960; Vazenin, 1975; Ginzburg, 1975). Soil organic matter (%) was determined by the Tiurin method (Orlov & Grisina, 1981), which is a wet combustion technique similar to the Walkley-Black method (USDA, 1995). Soil particle size analysis was based on separation of the mineral soil into various size fractions including gravel and coarser material, but the main procedure was applied to the fine-earth (B1 mm) fraction only. Analyses were performed at the Laboratory of the Kaltinenai Research Station of the Lithuanian Institute of Agriculture (LIA) using the particle-size analysis method of N. Kacinskij (Michmanova & Dolgov, 1966), which is commonly used in Eastern Europe. Comparisons of soil texture results by the Kacinskij and USDA methods were reported by Jankauskas and Fullen (2002). Soil sampling for soil bulk and particle density was performed on the mid-slope, when the same crop

Water erosion assessment Water erosion rates were assessed by measuring the length and cross-sectional area of rills to calculate soil loss volume (Zaslavskij, 1983; Watson & Evans, 1991; Chambers et al., 2000). Lost soil volume was calculated using the formula:  
X X X ln pn : n : y; (1) x lp l1 p1 . . . where x volume of erosion rills (m3 ha1); l, l1, . . . ln rill depth (cm); p, p1, . . . pn: rill width (cm, accuracy90.1 cm; n: number of rills on the measured plot width; y: measured plot width (m), and S: sum of nine measurements from selected 1 m length segments located at equal distances on the experimental plot). Data were transformed from m3 ha1 to Mg ha1 using mean soil bulk density (0
5 and 10
15 cm depth) from each site from the three slope segments. Equations relating soil loss to slope gradient were obtained from the mean annual data of 18 years using the ‘Microsoft Graph 97 Chart, Trendline Polynomial’. The significance of differences between treatment means was determined using Fisher’s LSD05 using the procedures of Tonku¯nas (1957) and Dmitriev (1966), which calculate mean errors for investigations of over three years duration (i.e., n3) using the formula: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi sx1 2  sx2 2  :::  sxn 2 (2) sx 9 n

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was grown in all treatments of the field experiment (i.e., on the field of perennial grasses in summer before stubble breaking, when preparing soil for winter rye). Soil samples were taken in rings of known volume and diameter. Samples were collected from 0
5 and 10
15 cm depths; however, the mean results from both depths are presented. Bulk density is the mass of a given volume of dry soil in its natural condition (the mass of the solids and the pore space) and was determined by removing a block of soil from site, allowing no compaction or crumbling. The soil was then dried and weighed and bulk density expressed in grams of oven-dry soil per cubic centimetre (Blake & Hartge, 1986; Motuzas et al., 1996). The particle density of soil is the ratio of the total mass of solid particles to their total volume. Soil volume was determined by the cyclometer method (Blake, 1965; Motuzas et al., 1996). Total soil porosity and moisture retention capacity are calculated from soil bulk density and particle density data (Motuzas et al., 1996). Soil structural stability was analysed using the Savinov-Bakseev method to determine dry and wet aggregate strength by dry and wet sieving (Fedorovskij, 1995). The method involves standard sieves with mesh diameters of 7, 5, 3, 1, 0.5 and 0.25 mm. The handset was used for dry sieving and two electro-motor sieve sets for wet sieving, as such sieving precludes operator influence. Aggregate fractions 1.0, 0.25
1.0 and B0.25 mm were used. Practical experience showed these measures enabled an assessment

m3 ha-1

of soil structure for agronomic purposes. Soil aggregate composition is influenced by crop type and stage, liming and irrigation (Fedorovskij, 1995). Therefore, soil aggregate stability was determined on soil samples taken before disking of grass after each crop rotation course in 1988, 1994 and 2000.

Results Soil erosion rates under different conditions Only spring barley and perennial grasses were grown every year in these investigations. In the experimental design there were different numbers of spring barley treatments (1
3) per year, which precludes meaningful statistical evaluation of soil erosion data from separate crops in different years. However, there was considerable annual soil loss variability under spring barley on the 5
108 slope (Figure 2). This included low values of 0.5
5.2 m3 ha1 (1992, 1995, 1996, 1997, 1998 and 2000), moderate values of 7.2
12.6 m3 ha1 (1984, 1987, 1988, 1990, 1993 and 1999) and high values of 22.4
72.6 m3 ha1 (1983, 1985, 1986, 1989, 1991 and 1994). The erosion-protection capability of different crops varied. Mean soil losses (1983
2000) under winter rye were 3.2, 6.7 and 8.6 m3 ha1 yr 1 and under spring barley were 9.0, 19.1 and 27.1 m3 ha1 yr1 from slopes of 2
58, 5
108 and 10
148, respectively. Perennial grasses prevented erosion almost completely, with only a small soil loss from

A

120

B

C

mm

P

1200

100

1000

80

800

60

600

40

400

20

200

0

2 0 00

1 9 99

1 9 98

1 9 97

1 9 96

1 9 95

1 9 94

1 9 93

1 9 92

1 9 91

1 9 90

1 9 89

1 9 88

1 9 87

1 9 86

1 9 85

1 9 84

1 9 83

0

Years of investigations 3

1

Figure 2. Soil losses (m ha ) from slopes of different gradient (columns) under spring barley and total precipitation (line). Columns: slopes of A: 2
58 (3.5
8.3%), B: 5
10o (8.3
17.7%) and C: 10
148 (17.7
26.3%). P: total precipitation (mm).

Lithuanian Albeluvisols under different management systems

71

-1

Mg ha

a

b

c

d

0 2.4 -5

9.9

A

2.5

7.5

B 4.9

-10

4.7

C

-15 18

7.2

7.4

23.4

-20 -25 -30

24.9 -35 32.2* A B C

LSD05 : A=0.88; B=1.9; C=1.44 Figure 3. Annual losses of soil due to water erosion under different crop rotations. The columns represent the mean data of 1983
2000 on slopes: A, 2
58; B, 5
108; C, 10
148. Crop rotations: a) field, b) grain-grass, c) grass-grain I, d) grass-grain II. *In accordance with standard agricultural policy in Lithuania potatoes were not grown on the 10
148 slope. The data were calculated by the method of group comparison.

the grass-grain I crop rotation due to poor red clover cover in 1992. Potatoes had least erosion-preventive capability, with mean soil losses from slopes of 2
58 and 5
108 being 8.7 times higher than under winter rye and 3.1 times higher than under spring barley. The erosion-preventative capabilities of different crop rotations under different land use systems varied widely (Figure 3). The mean annual losses of soil under grass-grain crop rotations decreased by 75
80% compared with the field crop rotation, while under the grain-grass crop rotation it decreased by 23
24%. However, even grass-grain crop rotations could not completely prevent water erosion, with mean annual losses of 7.2
7.4 Mg ha1 on the 10
148 slopes.

Changes in soil physical properties Natural soil fertility on the slightly, moderately and severely eroded slopes of the Zˇemaicˇiai Uplands has decreased, as mentioned in the Introduction, due to deterioration of soil physico-chemical properties. The percentage of clay-silt and clay fractions increased, while total porosity and moisture retention capacity decreased in the sequence noneroded, slightly, moderately and strongly eroded soils (Table I). Change of soil physical properties is a slow process; however, there were notable changes of soil dry bulk density under the influence of different land use systems after 18 years (Table II). The highest dry bulk density formed under the field crop

Table I. Dependence of selected soil physical properties on the severity of soil erosion on the arable (Ap) horizon of Eutric Albeluvisols (%) (n4 soil samples). Soil erosion severity Non-eroded Slightly eroded Moderately eroded Strongly eroded LSD05

Clay fraction (B0.001 mm)

Clay-silt fraction (B0.01 mm)

Soil porosity

Moisture retention capacity

11.6a 14.0b 19.1c 31.1d 2.22

24.6a 33.2b 37.4c 44.2d 2.30

28.9a 27.9b 24.8c 22.6d 0.99

42.6a 41.8b 39.3c 37.1d 0.04

Different letters after each number denote statistically significant (pB0.05) differences.

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Table II. Changes in the soil organic matter (SOM) and density characteristics of Eutric Albeluvisols under different land uses on eroded slopes, 2000. Dry bulk density (Mg m 3)

SOM (g kg1) on slopes of:

Treatments (crop rotations)

2
58

5
108

10
148

2
58

5
108

10
148

a) field or g)* b) grain-grass c) grass-grain I d) grass-grain II

1.66a 1.56b 1.47c 1.48c

1.68a 1.68a 1.57a 1.58a

1.37d* 1.54a 1.49b 1.44c

26.3a 29.9b 33.9c 34.6c

21.7a 20.1b 27.5c 26.7c

25.1b* 19.9a 24.5b 24.3b

LSD05

0.074

0.118

0.050

2.33

1.05

2.85

*Long-term sod-forming perennial grasses were grown instead of the field crop rotation on the 10
148 slope. Different letters after each number denote statistically significant (p B0.05) differences.

rotation. The more favourable conditions for plant growth were under the grass-grain crop rotations on all investigated sites, and under the long-term perennial grasses on the 10
148 slope. The highest SOM values were under the grass-grain crop rotations and sod-forming perennial grasses on the 10
148 slope. Generally, higher SOM values are associated with lower soil bulk densities. Correlation coefficients on slopes of 2
58, 5
108 and 10
148 were r 0.908, 0.875 and 0.814, respectively (n 12; p B0.001). Soil particle density ranged from 2.58 to 2.63 Mg m3 on the 2
58 slope, from 2.62 to 2.64 Mg m3 on the 5
108 slope and from 2.61 to 2.65 Mg m3 on the 10
148 slope. The slight increase in soil density with slope may be related to progressive loss of lighter surface organic coatings from the heavier mineral particles, but this hypothesis requires further investigation. Greater changes were evident in total soil porosity and moisture retention capacity (Table III). The lowest percentage total soil porosity and moisture retention capacity were under the field crop rotation and were significantly higher under the grassgrain crop rotations and especially under the

long-term sod-forming perennial grasses. Correlation coefficients between SOM% (x) and total soil porosity and moisture retention capacity (y1, y2) varied with slope steepness in the ranges r  0.930
0.838*** and 0.934***
0.810** (n 12, p B0.01**, pB0.001***), respectively. The lowest percentage of agronomically most useful soil aggregates (1 mm) (Fedorovskij, 1975) was on the 10
148 slope: 62
80% by dry sieving and 49
64% by moist sieving (Figure 4). This fraction was 73 and 91% (dry sieving) and 66 and 75% (wet sieving) on the 2
58 and 5
108 slopes, respectively. The correlation coefficient between SOM content and soil aggregates 1 mm is r 0.601 (n 12, p B0.05). Discussion An estimated 26 million hectares in the European Union suffer from water erosion and 1 million hectares from wind erosion (UNEP, 1992). The Mediterranean region is historically the most severely affected by erosion. However, quite high water erosion rates were estimated on the hilly-undulating

Table III. Changes in total soil porosity and moisture retention capacity under different land uses on the eroded slopes, 2000. Total soil porosity (%)

Moisture retention capacity (%) on slopes of:

Treatments (crop rotations) a) field b) grain-grass c) grass-grain I d) grass-grain II LSD05

2
58

5
108

10
148

2
58

5
108

10
148

35.9a 40.0b 43.9c 43.6c

35.8a 36.0a 40.5b 40.0a

48.2d* 41.0a 43.5b 45.7c

21.8a 25.7b 29.8c 29.5c

21.4a 21.5a 25.9b 25.4a

35.2c* 26.6a 29.3b 31.7b

2.69

4.45

2.16

2.72

4.39

2.82

*Long-term sod-forming perennial grasses were grown instead of field crop rotation on the 10
148 slope. There were four replications on slopes 2
58 and 5
108, and three replications on slopes of 10
148. Different letters after each number denote statistically significant (p B0.05) differences.

Lithuanian Albeluvisols under different management systems

73

D 100% 80% 60% 3

40% 2

20% 1

0% a

b

c

d

a

b

2-5°

c

d

g

5-10°

b

c

d

10-14°

M 100% 80% 60% 3

40%

2

20% 1

0% a

b

c

2-5°

d

a

b

c

5-10°

d

g

b

c

d

10-14°

Figure 4. Influence of crop rotations on dry (D) and moist (M) soil aggregate strength after third course of crop rotations in 2000. Treatments were: D: dry aggregate strength (by dry sieving method), M: moist aggregate strength (by moist sieving method); crop rotations: a: field, b: grain-grass, c: grass-grain I, d: grass-grain II, g: long-term sod forming perennial grasses were grown instead of the field crop rotation on the 10
148 slope. Soil aggregate fractions: (1)1 mm; (2) 1
0.25 mm; (3) B0.25 mm.

landscape of Lithuania (Figures 2 and 3). Moreover, in Lithuania tillage contributes to both water and wind erosion (Jankauskas, 2003; Jankauskas & Fullen, 2006). High water erosion rates on the sites of KRS field experiments were estimated starting in the early stages of the experiments. Soil losses were evident after every intense rain event and in each spring after snow melt. Differences in water erosion rates under different rotations and land use systems were evident after the first and further six-course crop rotations. However, changes in soil properties (bulk density, porosity, water holding capacity and organic matter content) became increasingly evident as the study progressed. These changes were hardy noticeable after the first crop rotation, but they became more evident after the second and especially after the third six-course rotation. Our observations can be supported by results from other investigators. Studies generally agree that soil organic matter physically

and chemically binds primary mineral particles together, thus increasing structural resistance to raindrop impact and splash. The consequent retention of large interstices between peds allows rapid infiltration, hence reducing surface flow (Fullen, 1991). Numerous field and laboratory studies have shown that soils with low organic matter contents are more erodible and that, generally, soils with B2% organic matter content are highly erodible (Fullen & Catt, 2004). There were notable changes in the dry bulk density of Eutric Albeluvisols under the influence of different land use systems after 18 years (Table III). The highest soil bulk density was under the field crop rotation, which also had the highest soil erosion rates, as reported above. Furthermore, the more eroded soil profiles were more truncated and very severely eroded soil profiles contained only Ap, Bt and Bt2 horizons above the BC horizon (Jankauskas & Fullen, 2002). Thus, more truncated

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B. Jankauskas et al.

soil profiles had developed under the field crop rotation compared with all other investigated land use systems during the 18-year period. Similar situations were described by Lal (1987) and Arriaga and Lowery (2004). The extent of soil profile truncation in Lithuania was influenced more by tillage erosion than water erosion (Kiburys, 1995; Jankauskas & Fullen, 2006). More favourable conditions for plant growth were found under the grass-grain crop rotations on all sites, and under the long-term perennial grasses on the 10
148 slope. The highest SOM values were found under the grass-grain crop rotations and under the sod-forming perennial grasses on the 10
148 slope. Generally, higher SOM values are associated with lower soil bulk densities. Comparable results were found at the Hilton Experimental Site, Shropshire, UK. (Fullen et al., 2002). Conversion of 10 plots from bare arable to grass ley set-aside reversed the trend of declining soil organic matter contents, which then significantly increased, especially in the first four years. Mean soil organic content (0
5 cm depth) significantly (p B 0.001) increased from 2.04% by weight (SD 0.45, n 50 samples) in April 1991 to 3.11% (SD 0.68, n 50 samples) in April 2001, compared with permanent grassland values of
4.5%. Soil erodibility after six years of set-aside (sampling date 24 April 1997) was determined using a drip-screen rainfall simulator. Soil aggregate stability was higher on the grassed soils, compared with set-aside and bare arable soils. Despite no significant (p 0.05) differences between grassland and set-aside soils, both these treatments were significantly (p B0.001) greater than the bare soils (Foster et al., 2000). Soil erosion alters important soil physico-chemical and biological properties necessary for optimal crop production. Topsoil is generally enriched with organic matter and has granular aggregates that provide larger soil pores, reduce soil density and enhance water infiltration and aeration. When topsoil is eroded, yield suffers due to nutrient loss and damage to soil physical properties. Topsoil loss and its impact on yield are more pronounced in soils on steep slopes (Lal, 1987). Erosion changes soil physical properties mainly because of the removal of surface soil rich in organic materials and exposure of lower soil layers. Bulk density and the saturated hydraulic conductivity of soil increased slightly with erosion rate (Arriaga & Lowery, 2004). Soil peds exist as complex and dynamic systems of micro- and macro-aggregates and affect many soil physical properties and microbiological processes (Fedorovskij, 1995). Results from the KRS longterm field experiments showed that the grass-grain crop rotations and sod-forming perennial grasses decreased soil erodibility, indicative of improved soil

structure, and these changes were associated with increased SOM contents (Figure 4 and Jankauskas et al., 2006). Low aggregate stability and the high dispersivity of soil with low organic matter contents allowed the development of a dense and thick crust for all soil aggregate sizes (Lado et al., 2004). Conversely, high aggregate stability and the low dispersivity of soils with high organic matter contents limited seal formation. The influence of different crop rotations was inconsistent in the case of dry sieving after the first course of crop rotations. However, it was evident that grass-grain crop rotations and sod-forming perennial grasses increased the soil aggregate fraction 1 mm in the case of wet sieving on the 10
148 slope (treatments c, d, g). These differences became more notable after the second crop rotation. The positive influence of grass-grain crop rotations on aggregate stability (1 mm) was evident on all investigated slopes. The most notable increase in soil aggregate stability (dry sieving) on grass-grain crop rotations and sod-forming perennial grasses was only evident after the third crop rotation (Figure 4). It was postulated that the largest increase in aggregate stability would be under perennial grasses, including leguminous grass, e.g., red clover (c), rather than cereal grass leys (d). However, the results of three six-course crop rotations (18 years) showed that there were no significant differences in soil aggregate stability between the different grass ley treatments (c, d). The multi-species agro-ecosystems of sod-forming perennial grasses and grass-grain crop rotations are potential components of viable soil conservation strategies. They can increase the soil carbon store, improve soil physical properties (i.e., total porosity, moisture retention, soil structure and aggregate stability) and minimize the risk of soil erosion and associated water pollution of both terrestrial and marine aquatic ecosystems. Therefore, the presented results may have important benefits for environmental protection, both nationally (increasing soil organic carbon and thus decreasing soil erodibility) and internationally (helping to ameliorate global warming).

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