F.J. Larney and H.H. Janzen

Land Resource Sciences Section

Agriculture and Agri-Food Canada Research Centre Lethbridge, Alberta Canada T1J 4B1

INTRODUCTION

The terms soil quality and soil health are currently used interchangeably in the scientific literature and popular press (Harris and Bezdicek, 1994). In general, soil scientists prefer soil quality and farmers prefer soil health. Soil degradation, which includes soil erosion, as well as soil salinity, soil compaction and organic matter decline, may be viewed as the reciprocal of soil health preservation (Sampson, 1981; Sparrow, 1984). Soil degradation, impacts on soil health which in turn impacts on soil productivity and crop yield.

Reasons for soil health degradation in Canada include abandonment of forage-based crop rotations for wide-row monoculture, increasing regional specialization with livestock farms located even further from crop farms leading to reduced regional requirements for forage crops, reduced frequency of forage or small grains in crop rotations, reduced use of manure where it is most needed, excessive use of summer fallow, expanding farm size, enlargement of fields, and shifts to more powerful heavier machinery (Dumanski et al., 1986).

In recent years, much attention has been focused on the prevention of further erosion by the adoption of conservation practices such as direct seeding, residue management or chemical fallow (Larney et al., 1994). However, little concern has been directed toward the restoration of eroded soils.

Many fields throughout the region have localized areas of low productivity associated with poor nutrient-supplying ability due to soil erosion. Producers have several options for correcting or compensating for soil erosion and remediating the productivity of these soils. The most common approach is to apply additional chemical fertilizer to eroded areas such as knolls to improve crop growth and reduce the potential for further erosion (Hamm, 1985). Application of livestock manure is another option where manure is available within a short hauling distance (Freeze et al., 1993). Mechanical replacement of topsoil is also possible (Verity and Anderson, 1990) but may be impractical on a large scale.

For farmers that do not have access to a manure supply, a possible restorative strategy may involve transporting crop residues (straw, hay) from productive areas to eroded areas of the farm. These residues could then be shredded and incorporated into the eroded surfaces, either alone, or in combination with chemical fertilizer to approximate a manure. However, the efficacy of such procedures in the restoration of soil productivity have not been field tested.

A lack of quantitative information exists on erosion-fertilizer-productivity relationships on the Chernozemic soils of western Canada. Many of these soils have shallow Ap horizons and excessive erosion often exposes highly calcareous B and C horizons. Fertilizer P may be immobilized by CaCO3 compounds making it unavailable for plant uptake (Doyle and Cowell, 1993). There is a need for more specific knowledge on the effects of topsoil loss on soil

productivity and the remedial effects of manures, crop residues and chemical fertilizers. By identifying interactions between erosion levels and amendments, producers may be able to apply these amendments at closer to optimum rates for given erosion levels within a field, and at the most efficient rate for the entire field.

Erosion-productivity studies on naturally eroded landscapes are confounded by many factors including variability in topsoil depth and soil moisture status. As a result, such studies are often conducted at sites where erosion has been simulated by mechanical topsoil removal (Dormaar et al., 1988; Massee, 1990; Ives and Shaykewich, 1987). In this manner, a wide range of topsoil depths, representative of various erosion classes, can be created. This approach does have some drawbacks (Cassel and Fryrear, 1990). Natural erosion selectively removes soil material during runoff or wind erosion events, a phenomenon which simulated erosion cannot duplicate. However, the simulated approach may be used to develop relationships between soil erosion, soil productivity and restoration of soil health.

SIMULATED EROSION EXPERIMENTS AT LETHBRIDGE RESEARCH CENTRE

Currently, there are four separate experiments examining the restoration of soil productivity or soil health to artificially eroded soils. For the purposes of this paper, crop productivity (yield) will be used as an indicator of restoration of soil health. High crop yield plays an important role in the restoration of soil health. Associated with high yields are high root densities which add to the organic matter pool after harvest, and high crop residue levels, which, if properly managed, improve soil structure and protect the soil surface from erosion.

Experiment 1 A

This experiment was superimposed on land levelled for irrigation in 1957 at the Lethbridge Research Centre, and has been reported on by Dormaar et al. (1988) and Freeze at al. (1993). The soil is a calcareous Dark Brown Chemozemic clay loam. The residual effects of manure and N and P fertilizer applied to a wheat-fallow rotation in 1980-85 are being monitored. Manure was applied at 30 t/ha in the fall of the fallow year (1980,1982 and 1984) to non-eroded (0 cm soil removed), moderately eroded (10-20 cm soil removed) and severely eroded (> 46 cm soil removed) land. Manure was last applied in fall 1984. Fertilizer N was applied as urea at 150 kg/ha and fertiliser P as triple superphosphate at 150 kg/ha in the spring of the cropped years (1981, 1983,1985)

Experiment 1 B

This study is at the same location as Experiment lA and comprises the same erosion levels. Residual effects of manure (40 t/ha in fall), fertilizer, and straw + fertilizer applied annually, and topsoil (3 cm) applied in 1987 for continuous cropping to wheat (1987-91) are being monitored on non-eroded, moderately eroded and severely eroded land. Manure was last applied in fall 1990. Fertilizer N was applied as ammonium nitrate at 100 kg/ha and P as triple superphosphate at 75 kg/ha. Straw + N fertilizer was applied each fall at a rate to match the nutrient content and C/N ratio of the manure.

Experiment 2

This study was initiated in 1990 at four sites representing the major soil groups in southern Alberta. Two sites were established on Dark Brown Chernozemic sandy clay loams at the Lethbridge Research Centre: one on dryland and one on irrigated land. A third site was established on a Brown Chernozemic clay loam at Taber, about 50 km east of Lethbridge, and a fourth site was established on a Black Chernozemic clay loam at Hill Spring about 75 km southwest of Lethbridge. All sites were established in the spring of 1990, except for the Hill Spring site which was established a year later. Two sites were also established in the Edmonton area of Alberta (Larney et al., 1995).

Topsoil was removed to 0, 5, 10, 15 and 20 cm by an excavator. Four amendment treatments were imposed as subplots on each cut: cattle manure, fertilizer N and P, 5 cm topsoil addition and check. Subplots were 3 x 10 m.

The manure rate was 75 t/ha wet weight as a one-time application in the first year of the study. Fertilizer N was applied as ammonium nitrate at 75 kg/ha and P as triple superphosphate at 50 kg/ha in the first year. All amendment treatments received recommended rates of N and P in subsequent years, except in 1993 when the fertilizer subplots received 400 kg/haP205 in an effort to overcome P-binding by the calcareous surfaces and ensure an abundance of plant available P.

All sites were direct seeded to spring wheat (cv. Lancer) using recommended seeding rates. The Lethbridge Irrigated site received adequate water to ensure that root-zone moisture was non-limiting. The Hill Spring site ran for two years (1991,1992) and the Taber site for four years (1990-93). The two Lethbridge sites have been continuously cropped for five years (1990-94). More detailed findings on this experiment may be found in Larney et al. (1991, 1992, 1993).

Experiment 3A

This experiment was carried out on adjacent plots at the four sites detailed in Experiment 2. The objective of this particular aspect of the study was to explore the effect of variable rates of N and P, and their interaction, in restoring productivity where topsoil had been mechanically removed to 0 cm, 10 and 20 cm.

Four rates of N were applied as randomized strips (2 x 12 m) on each of the erosion levels. Three rates of P were then applied in 4 x 8 m randomized strips perpendicular to the N treatments. The N rates (as ammonium nitrate) were 0, 25, 50 and 75 kg/ha at Lethbridge Dryland, Taber and Hill Spring and 0, 50, 100 and 150 kg/ha at Lethbridge Irrigated. The P rates (as P205, triple superphosphate) were 0, 25 and 50 kg/ha at Lethbridge Dryland, Taber and Hill Spring and 0, 50 and 100 kg/ha at Lethbridge Irrigated.

In the second year (1991 at Lethbridge Dryland, Lethbridge Irrigated and Taber; 1992 at Hill Spring), residual effects of the previous year's treatments on spring wheat were assessed.

All plots received a blanket application of 40 kg/ha of N (80 kg/ha at Lethbridge Irrigated) and 20 kg/ha of P (40 kg/ha at Lethbridge Irrigated) with the seed.

All sites were direct seeded to spring wheat (cv. Lancer). The Lethbridge Irrigated site received adequate water to ensure that root-zone moisture was non-limiting. This experiment ran for two years at each of the four sites.

Experiment 3B

After two years of cropping, Experiment 3A became Experiment 3B at three sites (Lethbridge Dryland, Lethbridge Irrigated and Taber). Four rates of cattle manure (0, 24, 48 and 72 t/ha, wet weight) replaced the four N fertilizer treatments for the 1992 cropped year. Three rates of P fertilizer were applied: zero, recommended and 3 x recommended rate. Manure was a one-time application in spring 1992. The plots have been continuously cropped to spring wheat. The Taber site was discontinued after 2 years of this particular study at the end of the 1993 growing season.

Experiment 4

This experiment is the most recent of the simulated erosion studies at Lethbridge Research Centre and focuses on a wide range of amendatory treatments aimed at restoring soil health (Larney and Janzen, 1994). The study is located 5 km east of Lethbridge on a sandy clay loam Dark Brown Chernozemic soil. In May 1992, 15 cm of topsoil was mechanically removed with an excavator to simulate erosion. The plot layout was a randomized complete block design with four replications of fourteen amendments. The plots were 10 x 6 m. The amendments included six animal manures: fresh, old, and composted cattle manure, cattle manure + wood shavings, hog manure, poultry manure; four crop residues: alfalfa hay, pea hay, barley straw + 200 kg/ha of N, barley straw + 200 kg/ha of P205; two phosphate fertilizer rates: 200 and 400 kg/ha of P205; and two checks: eroded check (topsoil removed, no amendment), and topsoil check (no topsoil removed, no amendment).

The fresh cattle manure was about 6 months old and contained a large amount of wheat straw. The old cattle manure was from the same source but had been stockpiled for 2-3 yr. The composted manure came from a different source, and had been composted for 1 yr in large windrows which were regularly aerated. The poultry manure was from a broiler operation where wheat straw was used as litter. The solid hog manure was from a farrowing unit and contained wheat straw. The alfalfa hay, pea hay and barley straw had been harvested and baled in summer 1991. All amendments were applied on a dry weight basis at a rate of 20 t/ha. The amendments were incorporated into the soil surface to 10 cm depth with a rototiller. Spring wheat was direct seeded in 1992, but was destroyed by a severe hail storm on August 2. No further amendments were applied and the site was cropped to spring wheat in 1993 and 1994. Before seeding in 1993, surface soil samples were taken for extractable P concentration and aggregate stability (Kemper and Rosenau, 1986). More detailed results on the effects of the soil amendments on soil structural improvement may be found in Sun et al. (1994a, 1994b).

SUMMARY OF RESEARCH RESULTS

Experiment 1A

Ten years after the last manure was applied to the eroded soils, residual yield effects were still evident (Table 1), especially on the moderate and severe erosion treatments. Residual fertilizer effects were less distinct, especially on the moderate and sever erosion treatments.Table 1. Effect of erosion level and residual amendments on grain yield in 1994 (amendments

Experiment 1B

An erosion x amendment interaction for 1994 grain yield showed that there was less difference in amendment treatments on the 0 cm cut than on the 10-20 and > 46 cm cuts (Table 2). Residual manure effects were still strong on the deeper cuts. Residual effects for the fertilizer amendment (N + P) were stronger than those of the straw + N fertilizer but only on the 0 and 10-20 cm cuts. The benefits of 3 cm of topsoil application were negligible seven years after the topsoil was applied.

Experiment 2

Yields were very high in 1994, due to above normal precipitation in fall 1993 and good growing season precipitation (Table 3). The manure amendment was the highest-yielding at all levels of erosion even after 5 years of continuous cropping. However, its effects were less distinct on the irrigated site probably due to the higher biomass production over the study period and also leaching of nutrients under irrigation. The topsoil amendment was the second highest yielding amendment at all levels of erosion. The high rate of P205 applied in 1993 did not have any effect on 1994 yields as there was little yield difference between the check treatment and the fertilizer treatment at all erosion levels at both sites.Table 2. Effect of erosion level and residual amendments on grain yield in 1994 (manure, fertilizer, straw + fertilizer applied annually between 1986 and 1990; 3 cm topsoil addition applied in 1987).

Amendment Depth of topsoil removal, cm

0 10-20 > 46

t ha~'

Check 2.3 0.8 0.5

Fertilizer 3.7 2.4 1.0

Manure 3.8 3.3 2.8

Straw 3.2 0.9 1.2

Topsoil 2.6 1.0 0.7

LSD005 = 0.6 t/ha

Table 3. Spring wheat grain yields at Lethbridge Dryland and Irrigated sites, 1994.

Amendment Depth of Cut

0cm 5cm 10cm 15cm 20cm

t ha~1

Lethbridge Dryland

Check 4.3 3.7 3.3 2.8 2.7

Fertilizer(1) 4.7 3.8 3.8 3.2 3.2

Manure(2) 5.3 5.2 4.9 4.8 5.0

TOp5Ojl(3) 4.8 4.5 4.1 3.9 3.9

Lethbridge Irrigated

Check 6.2 5.0 3.8 3.6 3.9

Fertilizer(1) 6.5 5.3 4.0 3.5 3.4

Manur(2) 7.0 6.1 5.3 4.6 4.5

TOp5Oil(3) 6.5 5.6 4.7 4.4 4.1

(1) Received an extra 400 kg/ha of P205, spring 1993. (2) 50 t/ha applied, spring 1990. (3) 5 cm topsoil applied, spring 1990

The yield response to manure increased as the level of erosion increased at all four sites (Table 4). The results demonstrate that applying manure on low-yield potential areas of a field (e.g. eroded knolls) is likely to give a better return than application to high yield potential areas.

Table 4. Wheat yield increases with manure application at Lethbridge Dryland and LethbridgeIrrigated (average 1990-94); Taber (average 1990-93); and Hill Spring (average 1991-92).

Depth of Cut, Lethbridge Lethbridge Taber Hill Spring

cm D~and Irrigated

t ha~1

0 0.5 0.5 0.3 1.1

5 0.6 0.5 0.7 1.6

10 1.3 1.0 0.9 2.0

15 1.4 1.3 0.7 2.2

20 1.6 1.4 1.2 2.2

Experiment 3A

In the initial year, using data from the check treatments on the non- and moderately eroded plots, grain yield losses due to moderate erosion (10 cm topsoil removal) were 50% at

Lethbridge Dryland, 43% at Lethbridge Irrigated, 66% at Taber and 61 % at Hill Spring. Lethbridge Dryland was the only site where yield loss on the moderately eroded soil was fully restored by N and P fertilizer. Yield losses were only partially restored at the other three sites, being mitigated to 23 % at Lethbridge Irrigated and 34% at both Taber and Hill Spring by addition of the highest rates of N and P.

Yield losses due to severe erosion (20 cm top soil removal) were reduced from 74% to 46% at Lethbridge Dryland, from 84% to 59% at Lethbridge Irrigated, from 60% to 58 % at Taber and from 85% to 53% at Hill Spring by addition of the highest rates of N and P.

At Lethbridge Dryland, Lethbridge Irrigated and Taber, the largest grain yield response to fertilizer occurred on moderately eroded soils (0.42-0.92 t/ha), followed by severely eroded soils (0.27-0.55 t/ha) and non-eroded soils (0.16-0.45 t/ha). Thus moderately eroded areas were more responsive to chemical fertilizers than were severely or non-eroded soils. At Hill Spring, however, the non-eroded treatment showed the largest difference between highest and lowest-yielding treatments (0.97 t/ha), followed by the moderately eroded soils (0.6 t/ha) and the severely eroded soil (0.52 t/ha

On moderately and severely eroded soils, there was evidence of a synergistic fertilizer effect, as N and P applied together resulted in highest grain yields at all four sites in the initial year. Tanaka and Aase (1989) reported that P was the most limiting nutrient in a topsoil removal study in Montana and that additions of N fertilizer without P resulted in only small yield increases. In our study, P alone was generally more effective than N alone at increasing grain yields at Lethbridge Dryland and Lethbridge Irrigated though some exceptions were evident.

Treatment effects on yield at the Lethbridge Irrigated site followed a similar pattern to the dryland sites which demonstrates that erosion effects on soil productivity are not compensated by adequate soil water even with high rates of fertilizer addition.

In the second cropped year, grain yield differences between fertilizer treatments on the non-eroded and moderately eroded treatments were less than in the initial year, implying that the previous year's crop with its associated roots and residues, had, to some extent, restored productivity to moderately eroded plots.

Experiment 3B

Table 5 illustrates the effect of manure rate in restoring crop productivity at three levels of erosion for 1992 and 1993. At all sites in both years, the erosion response to manure ranked: 20 cm > 10 cm > 0 cm cut. Averaged over sites and years, the highest rate of manure resulted in a 36% yield increase on the 0 cm cut, a 128% increase on the 10 cm cut and a 172% increase on the 20 cm cut, compared with the non-manured treatment. In all cases, the 20 cm cut that received the highest manure rate outyielded the non-manured 0 cm cut. The highest manure rate generally masked the effect of topsoil removal (Table 5). There was evidence of a plateau effect of manure rate on the 10 and 20 cm cuts at Lethbridge Irrigated in 1992 and 1993. Application of 72 t/ha did not significantly increase yield over the 48 t/ha rate. In general the largest yield response occurred between the 0 and 24 t/ha rates of manure, especially on the 10 and 20 cm cuts.

Experiment 4

The 1992 results showed that hog manure, poultry manure, alfalfa hay, old and composted cattle manure were capable of restoring productivity to the capacity of the topsoil check treatment (Table 6). There was no significant yield difference between any of the livestock manures, except that the hog manure was significantly higher yielding than the fresh cattle manure. The alfalfa hay was just as efficient as the livestock manures. The pea hay was as good as all the livestock manures except hog manure. Barley straw + 200 kg/ha of P205 was as beneficial as the three types of cattle manure. Adding P205 to barley straw resulted in significantly higher yields than adding N.

In 1993, there was no significant yield difference between hog, poultry, old cattle, fresh cattle manure, 200 kg/ha P205, 400 kg/ha P205 or alfalfa hay. Composted cattle manure yielded significantly lower than poultry and hog manure. Compared with the 1992 results, the 200 and 400 kg/ha P205 treatments showed increased effectiveness in 1993 in reducing the impact of erosion. The P205 may be more available in the second year as P-binding carbonates are leached from the desurfaced plots. The composted cattle manure, alfalfa hay and pea hay and straw + 200 kg/ha P205 showed reduced effectiveness in the second year while poultry, hog, old cattle and fresh cattle manure showed similar effectiveness in both years.Table 5. Effect of manure rate on grain yield at three levels of erosion, 1992,1993.

Manure 1992* 1993

rate

Depth of topsoil removal, cm

0 10 20 0 10 20

t ha~'

t ha~1 Lethbridge Dryland

0

0 1.5 0.6 0.6 5.1 3.0 3.0

24 2.5 1.4 1.7 6.0 4.4 4.1

48 2.6 1.6 2.1 6.3 5.6 4.8

72 2.9 2.3 2.7 6.3 6.1 6.0

Lethbridge Irrigated

0 3.0 1.5 1.1 5.7 5.5 4.8

24 4.2 3.3 2.7 5.5 6.3 5.6

48 4.3 4.6 3.8 5.8 6.1 5.8

72 4.3 4.0 3.9 6.0 6.4 6.1

Taber

0 4.0 2.0 1.7 5.0 3.1 2.3

24 4.3 3.9 3.4 6.1 3.7 3.1

48 4.5 4.4 4.7 7.1 4.8 4.5

72 4.5 4.6 4.8 6.8 5.2 5.0

In 1992, straw yields are presented for Lethbridge Dryland and Taber as a late-season drought prevented grain-fill hence masking the true treatment effect on grain yield. In 1992, mid-season biomass yields are presented for Lethbridge Irrigated as a severe hailstorm on August 2, caused 100% crop damage.

In 1994, The poultry and hog manure treatments showed no evidence of reduced effectiveness even after three years of cropping. The straw/fertilizer treatments which yielded poorly in the first two years showed improved effectiveness in the third year, probably due to the slower decomposition of fresh straw residue which tied-up nutrients in the early part of the study.

In all years, yields from desurfaced plots amended with hog or poultry manure were not significantly different from plots with no topsoil removal, while yields from the cattle manure + wood shavings, and the barley straw + 200 kg/ha N treatments were not significantly different from the eroded check treatment. There was little yield difference due to age of cattle manure. Averaging all years, the fresh or old cattle manure was slightly better at restoring productivity than the composted cattle manure.Table 6. Effect of amendment on biomass yields (1992), grain yield (1993,1994), extractable P concentrations (0-7.5 cm depth), and water stable aggregates (WSA), spring 1993.

Amendment 1992 1993 1994 Extr. WSA

__________________ P

tha~1 'Lgg~1

Fresh cattle manure 2.5 6.0 4.3 7 38

Old cattle manure 3.1 6.1 3.4 20 32

Composted cattle manure 2.9 5.1 3.4 15 37

Cattle manure + wood shavings 1.6 5.3 3.9 2 31

Hog manure 4.0 6.7 5.9 52 46

Poultry manure 3.6 6.5 6.2 31 40

Alfalfa hay 3.3 5.7 5.3 4 46

Pea hay 2.6 5.1 3.9 2 48

Barley straw + 200 kg ha' N 0.7 4.3 4.0 1 48

Barley straw + 200 kg ha4 P2O~ 2.0 4.8 3.5 15 45

200 kg/ha P205 1.6 5.9 3.0 14 30

400 kg/ha P205 2.0 5.8 2.7 28 29

Eroded check 1.2 4.4 3.4 1 29

Topsoil check 3.7 7.3 6.1 9 27

LSD(P<0.05) 1.3 1.2 1.2 20 7

The yield-restoring capability of the hog and poultry manure treatments may lie in their higher P-supplying power (Table 6). Seven of the treatments were able to supply P in excess of the non-eroded topsoil check treatment, while six were not.

Percent water stable aggregates (Kemper and Rosenau, 1986) may be used as an index of restoration of soil health as it is a measure of susceptibility to water erosion: the lower the value then the higher the erosion risk. The crop residues were more effective in increasing aggregate stability then the animal manures (Table 6). Crop residues either alone (pea and alfalfa hay) or in combination with fertilizer (barley straw + N or P205) resulted in higher stabilities than animal manures which were in turn higher than the fertilizer alone treatments (200 and 400 kg/ha P205). This is likely related to more readily available organic material in the crop residues compared with the livestock manures.

PRACTICAL IMPLICATIONS FROM RESEARCH FINDINGS

1. Our results showed that drastic yield reductions followed topsoil removal to simulate erosion, and that chemical fertilizer, while having some remedial action, was a poor surrogate for topsoil even with adequate moisture under irrigation. These findings are probably attributable to the ineffectiveness of P fertilizers in calcareous soils. Our findings confirm that (i) increased adoption of soil conservation practices is required to avert topsoil removal by erosion in the first place; (ii) if soil health is to be restored, then manure is a better option than fertilizer.

2. P supplied from manure was apparently more available for plant uptake than P supplied by chemical fertilizers in the calcareous layers exposed to the surface by simulated erosion of the study soils. A very high rate of P205 (400 kg/ha) was ineffective in combating the high P-binding effect of the calcareous soil surfaces.

3. Residual effects of manure were evident even after 10 years of continuous cropping under dryland conditions. Under irrigation, residual manure effects may not be as long-lasting due to increased removal of nutrients in the higher biomass yields produced or potential leaching of nutrients by irrigation water.

4. On the amendment study, the overall best amendments were hog and poultry manure, followed by alfalfa hay. The alfalfa and pea hay were generally as good as the fresh, old or composted cattle manures. The barley straw + fertilizer N and P did not prove to be an effective approximation of manure. The effect of amendment on aggregate stability (which is an index of soil quality or health was of the order crop residues > livestock manures > fertilizer/check treatments.

5. Our results have implications for the 'farming by soil' and the 'variable rate technology' concepts currently in vogue. In agricultural landscapes there are areas of inherently high and low productivity due to past erosion events. Manure rates may be varied to match erosion levels. Non-eroded areas may give very low responses to manure. Moderately eroded areas (equivalent to the 10 cm cut) and especially severely eroded areas (equivalent to the 20 cm cut) can accommodate higher manure rates with corresponding yield increases.

ACKNOWLEDGEMENTS

The following funding sources are acknowledged: Canada-Alberta Soil Conservation Initiative (CASCI); Canada-Alberta Environmentally Sustainable Agriculture Agreement (CAESA); Alberta Agricultural Research Institute (Farming For The Future Research Program). We thank B.M. Olson, Caledonia Terra Research, Lethbridge who contracted part of this research. The technical help of A.W. Curtis and E.C.S. Olson is gratefully appreciated.

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