**3.1.2 Soil type**

184 Soil Erosion Studies

Soil loss decreased with increasing levels of peat in the three soils. This was true irrespective of the compaction effort, and the rainfall duration that the three soils were exposed to. The decrease in soil loss by peat content confirms the earlier findings in the previous papers by Ekwue et al. (2009) and Ekwue and Harrilal (2010) that peat decreases soil erosion by water.

Piarco 0 12.6 24.3 50.2 75.8 13.7 25.1 52.8 77.8 15.1 28.0 54.3 82.2

sandy 5 10.3 21.4 45.8 68.3 11.5 23.0 46.9 70.6 13.4 25.0 48.7 76.1

loam 10 7.1 17.2 38.3 58.1 8.3 18.3 38.1 63.3 10.5 20.1 44.0 70.5

Maracas 0 14.1 26.7 53.2 80.0 15.2 28.7 55.1 82.3 16.2 30.1 61.7 84.2

clay 5 12.3 23.8 48.2 73.7 13.1 26.0 51.3 76.8 14.0 27.3 55.1 78.3

loam 10 9.8 19.3 42.1 65.2 11.3 23.8 47.9 70.3 12.1 24.9 49.0 74.1

Talparo 0 16.9 28.3 55.2 84.2 16.4 31.9 59.4 87.7 17.1 31.4 63.0 90.1

clay 5 15.0 25.1 51.1 79.0 14.3 27.1 54.8 82.0 15.2 28.1 58.1 84.0

This is in line with the findings of Ekwue and Stone (1995) and Ekwue et al. (2009) which showed that peat reduces bulk density of soils by diluting the soil matrix with its own less dense material. This reduction in soil bulk density ensured that peat increased the infiltration capacity of the soils, and therefore reduced runoff and soil loss as was further confirmed in this study (Tables 2, 3, and 4). Ekwue (1987, 1992) reported increases in infiltration rates as a result of peat incorporation to the soil. Table 6 shows that penetration resistance decreased with increasing peat contents in all the soils. This result is in agreement with the findings of Ekwue (1990) and Zhang et al. (2005) which showed that peat reduces soil strength. Peat reduces soil strength by just adding to the soil bulk, reducing its inter-aggregate stability and making the soil aggregates to fall apart (Ekwue,

Table 3. Surface runoff (mm) of soils at varying peat, compaction levels and rainfall

10 12.3 23.8 47.8 72.7 12.6 25.0 50.7 75.7 14.1 26.3 53.1 79.9

Compaction Effort, 150 kPa

Rainfall duration (min)

5 10 20 30 5 10 20 30 5 10 20 30

Compaction Effort, 185 kPa

Rainfall duration (min)

This can be attributed to its reduction of soil bulk density (Table 6).

Compaction Effort, 100 kPa

Rainfall duration (min)

**3.1.1 Peat content** 

Soil Type

durations

Peat Content (%)

> The main effect of soil type was the second most important of all the experimental factors on soil loss and runoff (Table 5). This was almost like the previous paper by Ekwue and Harrilal (2010) where it was the most important factor. This may be as a result of the same process involved in the raindrop erosion measured in the two studies. In a previous study by Ekwue et al. (2009), soil type was the least important factor and this may be because this study measured wash erosion by surface runoff, while the present and the Ekwue and Harrilal (2009) examined the total erosion process of transport of soil particles detached by raindrop which is commonly referred as interrill erosion (Levy et al., 2001). Piarco sandy loam had the largest quantity of mean soil loss and this has been consistent in the with these two recent studies. Although this soil had the least runoff as the rainfall duration increased (Tables 3 and 4), its low percentage clay content (18.1%, Table 1) decreased the soil strength (Table 6), thus decreasing the soil's ability to increase the cohesiveness of the particles. The larger size of the sandy loam soil led to greater presence of large pores which enhanced infiltration. Results show that this led to lower surface runoff. However, decreased soil cohesiveness, the presence of more loose detached sand particles ensured that the soil had greater soil loss than the other soils despite its maintenance of high infiltration and low runoff rates.

> With the 46.3% clay content of the Talparo clay soil (Table 1), the soil cohesiveness and soil strength (Table 6) was the greatest as was measured by the soil penetration test. However, due to the low infiltration and high runoff rates recorded for this soil, the Talparo soil still had more soil loss than the Maracas clay loam soil. Although there was little raindrop detachment, due to the quantity of clay in the soils composition, the Talparo clay experienced the lowest infiltration and greatest amount of surface runoff of the three soils (Tables 3 and 4). This quantity of surface runoff was able to produce soil erosion, and as the rainfall duration increased, so too did the runoff and also the quantity of erosion. However, its high clay composition and high soil strength ensured that there was less erosion than the Piarco sandy loam. The Maracas clay loam had the least soil loss. This was mainly its evenly balanced composition of sand, silt and clay (Table 1). The Maracas clay loam had 30.6% clay content which was enough to produce good cohesive nature and soil strength for the particles so as to minimize splash erosion and easy detachment. The sand and silt composition allowed the soil to have steady infiltration throughout the testing period and leading to runoff which was closer to that recorded for the sandy loam soil (Table 4). These

Soil Loss-Rainfall Duration Relations as Affected

Soil type x compaction

Peat content x compaction

Compaction effort x

\*Significant at 0.1% level

by Peat Content, Soil Type and Compaction Effort 187

Sources of variation Degrees of freedom Runoff Soil loss

Soil type 2 50.3\* 166.7\*

Peat content 2 50.5\* 79.1\*

Compaction effort 2 27.1\* 99.5\*

Rainfall duration 3 2002.2\* 1915.7\*

Soil type x peat content 4 0.6 0.2

effort 4 0.8 1.9

Soil type x duration 6 4.5\* 29.4\*

effort 4 0.8 0.8

Peat content x duration 6 1.9 11.8

duration 6 3.1\* 27.2\*

Soil type Added peat Bulk density, t m-3 Penetration resistance,

Piarco sandy loam 0 1.47 1.57 1.68 150.1 157.5 165.7

Maracas clay loam 0 1.42 1.45 1.51 160.0 171.0 180.1

Talparo clay 0 1.20 1.25 1.28 172.8 184.8 205.1

Table 6. Values of bulk density and penetration resistance of soils prior to testing for soil loss

kPa

kPa

Compaction effort, kPa

100 150 185 100 150 185

5 1.37 1.47 1.56 147.2 152.8 160.5 10 1.24 1.28 1.42 129.3 143.6 154.7

5 1.21 1.24 1.33 153.6 165.9 172.4 10 1.04 1.07 1.12 147.8 155.6 167.4

5 1.15 1.21 1.23 163.5 170.7 189.2 10 1.12 1.17 1.20 156.7 163.0 174.1

Table 5. 'F' values in the analysis of variance for cumulative runoff and soil loss

Content, %

Compaction effort,


characteristics of low soil detachment and medium runoff made the Maracas clay soil to have the least soil loss of the three soils.

a] Mean values for each factor were obtained by averaging the measured values over the levels of the other three experimental factors. Values followed by different letters in each column are significantly different at the 0.1% level. Number of experimental points is 216 representing a factorial experiment with 3 soil types, 3 levels of added peat, 3 compaction levels, and 4 rainfall durations with 2 replications.

Table 4. Mean values of cumulative runoff and soil loss for different experimental factors[a]

characteristics of low soil detachment and medium runoff made the Maracas clay soil to

(mm)

Piarco sandy loam 37.1 a 1.36 c Maracas clay loam 41.6 b 0.95 a Talparo clay 44.7 c 1.27 b LSD (P = 0.001) 2.0 0.06

0 44.7 c 1.34 c 5 41.5 b 1.20 b 10 37.1 a 1.04 a LSD (P = 0.001) 2.0 0.06

100 38.2 a 1.34 c 150 41.3 b 1.23 b 185 43.8 c 1.01 a LSD (P = 0.001) 2.0 0.06

5 13.1 a 0.38 a 10 25.1 b 0.71 b 20 51.0 c 1.42 c 30 75.3 d 2.27 d LSD (P = 0.001) 2.5 0.08

a] Mean values for each factor were obtained by averaging the measured values over the levels of the other three experimental factors. Values followed by different letters in each column are significantly different at the 0.1% level. Number of experimental points is 216 representing a factorial experiment with 3 soil types, 3 levels of added peat, 3 compaction levels, and 4 rainfall durations with 2

Table 4. Mean values of cumulative runoff and soil loss for different experimental factors[a]

Mean soil loss (kg)

have the least soil loss of the three soils.

Soil type

Peat content, %

Compaction effort, kPa

Rainfall duration (mins)

replications.

Factor level Mean runoff


Table 5. 'F' values in the analysis of variance for cumulative runoff and soil loss


Table 6. Values of bulk density and penetration resistance of soils prior to testing for soil loss

Soil Loss-Rainfall Duration Relations as Affected

effort and(c) peat content on soil loss.

duration.

**3.1.3 Rainfall duration** 

**3.1.4 Compaction effort** 

by Peat Content, Soil Type and Compaction Effort 189

(c) Fig. 3. Effect of the interactions between rainfall duration and (a)soil type, (b) compaction

The interaction between soil type and rainfall duration (Fig. 3), was significant and shows that as the rainfall duration increased the differences in soil loss between the sandy soil and the clay loam and clay widened. This was similar to the results obtained by Ekwue (1991). Results, therefore, confirm that the effect of soil type on soil erosion depends on the rainfall

As expected, soil loss increased, in each case with rainfall duration. At higher rainfall duration, there was a greater breakdown in soil aggregates as well as greater cumulative runoff on the soil surface. The magnitude of increase of soil loss with increasing rainfall duration was, however, reduced by increasing peat content, clay content and soil compaction effort as the interactions between rainfall duration and these three parameters

Generally, soil loss decreased with increasing compaction effort in all the soils and this further clarifies the effect of compaction on soil loss. Soil compaction is a process by which soil particles are rearranged into a denser state. This is normally caused by natural forces or human induced mechanical loads such as wheel traffic and tillage. It results in reduction in soil porosity mainly its air-filled fraction, decrease in aeration and water infiltration, and increase in soil strength (Tekeste et al., 2006**).** Although surface runoff increased with increasing compaction effort (Table 3), the greater soil strength which resulted from compaction (Table 6) ensured that soil loss declined with increasing compaction levels. This

showed (Fig. 3). These results are not very explicit in previous studies of soil erosion.

(b)

(b)

(a)

Fig. 3. Effect of the interactions between rainfall duration and (a)soil type, (b) compaction effort and(c) peat content on soil loss.

The interaction between soil type and rainfall duration (Fig. 3), was significant and shows that as the rainfall duration increased the differences in soil loss between the sandy soil and the clay loam and clay widened. This was similar to the results obtained by Ekwue (1991). Results, therefore, confirm that the effect of soil type on soil erosion depends on the rainfall duration.

#### **3.1.3 Rainfall duration**

As expected, soil loss increased, in each case with rainfall duration. At higher rainfall duration, there was a greater breakdown in soil aggregates as well as greater cumulative runoff on the soil surface. The magnitude of increase of soil loss with increasing rainfall duration was, however, reduced by increasing peat content, clay content and soil compaction effort as the interactions between rainfall duration and these three parameters showed (Fig. 3). These results are not very explicit in previous studies of soil erosion.

#### **3.1.4 Compaction effort**

Generally, soil loss decreased with increasing compaction effort in all the soils and this further clarifies the effect of compaction on soil loss. Soil compaction is a process by which soil particles are rearranged into a denser state. This is normally caused by natural forces or human induced mechanical loads such as wheel traffic and tillage. It results in reduction in soil porosity mainly its air-filled fraction, decrease in aeration and water infiltration, and increase in soil strength (Tekeste et al., 2006**).** Although surface runoff increased with increasing compaction effort (Table 3), the greater soil strength which resulted from compaction (Table 6) ensured that soil loss declined with increasing compaction levels. This

Soil Loss-Rainfall Duration Relations as Affected

Experimental Station Bulletin 670.

Thesis, Cranfield University, U.K.

Tillage Research 23, 141 – 151.

Biosystems Engineering 105, 112 – 118.

Society of America Journal, 67:637-644.

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Trinidadian soils. Biosystems Engineering 102, 236 – 243.

Lambe T W (1951). *Soil Testing for Engineers*. New York: John Wiley.

by Peat Content, Soil Type and Compaction Effort 191

Christiansen J E (1942). Irrigation by Sprinkling. University of California Agricultural

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Ekwue E I (1990). Effect of organic matter on splash detachment and the processes involved.

Ekwue E I (1991). The effects of soil organic matter content, rainfall duration and aggregate

Ekwue E I (1992). Quantification of the effect of peat on soil detachment by rainfall. Soil and

Ekwue E I; Stone R J (1995). Organic matter effects on the strength properties of compacted

Ekwue E I; Bharat C; Samaroo K (2009). Effect of soil type, peat and farmyard manure

Ekwue, E I; Harrilal, A. (2010). Effect of soil type, peat, slope, compaction effort and their

Gumbs FA (1987). Soil and Water Conservation Methods for the Caribbean, Trinidad: Department of Agricultural Extension, University of the West Indies.

Lebeau B; Barrington S; Bonnell, R (2003). Micro-tensiometers to monitor water retention in peat potted media. Applied Engineering in Agriculture 19 (5), 559 – 564. Levy G J; Shainberg J; Letey J (2001). Temporal changes in soil erodibility. In: Soil Erosion

Ascough II and D. C. Flanagan. St. Joseph, Michigan: ASAE., #701P0007 Morgan R P C (2005): *Soil Erosion and Conservation*, 3rd edition, John Wiley, New York. Ohu J O; Raghavan G S V; Mckyes E. (1985). Peatmoss effect on the physical and hydraulic characteristics of compacted soils. Transactions of the ASAE 28, 420 – 424. Rachman A; Anderson S H; Gantzer C J; Thompson A L (2003). Influence of longterm

addition, slope and their interactions on wash erosion by overland flow of some

interactions on infiltration, runoff and raindrop erosion of some Trinidadian soils.

Research For the 21st Century, Proc. Int. Conf. Honolulu, Hawaii, USA), eds. J. C.

cropping systems on soil physical properties related to soil erodibility. Soil Science

surveys, 2nd Edition, Agriculture Handbook 436, 128 – 129. USDA, Washington-

element analysis of cone penetration in layered sandy loam soil: considering the precompression stress state. In Zazueta F; Kin J; Ninomiva S; Schiefer G. (Eds.), Computers in Agriculture and Natural Resources, 4th. World Congress Conference,

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Soil Survey Staff (1999). Soil taxonomy: A basic system for making and interpreting soil

Tekeste M Z; Tollner E W; Raper R L; Way T R; Johnson, C E (2006). Non-linear finite

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Orlando, Florida, USA, ASABE Publications No. 701P0606.

Canadian Agricultural Engineering 32: 215 – 223.

result is not always certain since it is always feared that greater surface runoff as a result of soil compaction could increase soil erosion.

#### **3.2 Derivation of regression equation relating soil loss to experimental factors**

The soil loss for the three soils with three levels of peat content compacted at three levels and exposed to four rainfall durations was used to generate a multiple linear regression equation that could be used to predict soil loss. The equation was of the form:

$$\text{SL} = 0.767 \text{ - } 0.00276 \text{ C}\_{\text{t}} \, 0.0307 \text{ P}\_{\text{t}} \, \text{- } 0.00386 \text{ P}\_{\text{c}} + 0.00172 \text{ KE} \tag{1}$$

$$\text{Student 't' (11.34) (-7.62) (-4.43) (-3.69)} \tag{8.70}$$

$$\text{(R = 0.878; N = 216)}$$

Where: SL is soil loss (kg); Ct is clay content of the soil (%); Pt is the peat content (%), Pc is compaction effort (kPa) and KE is raindrop kinetic energy (J m-2). R is the coefficient of multiple regression and N is the number of experimental data points. The signs of the experimental factors obtained confirm how the factors affected the soil loss. The R is significant at the 0.1% level. The student 't' values for all the experimental factors shown beneath them in the equation were all significant at 0.1% level. The relative 't' values for all the factors also confirm the findings in the analysis of variance which showed that the most important factors that affected soil loss were rainfall duration, soil type, compaction effort and peat content.

## **4. Conclusion**

Soil loss by simulated rainfall was measured for three Trinidadian soils in the laboratory using a specially constructed soil erosion apparatus. Soil loss decreased with increasing peat content in all cases and was smallest in the clay loam soil and highest in the sandy loam. Peat decreased soil loss by decreasing runoff during rainfall. Soil loss declined with increasing compaction effort. The interactions involving rainfall duration showed that although soil erosion increases with rainfall duration, these increases will be reduced by increasing clay, and peat contents of the soil as well as the increasing level of soil compaction. A multiple regression equation derived to relate soil loss to the experimental factors was highly significant and confirmed that the most important factors that affected soil loss were rainfall duration, soil type, compaction effort and peat content. The implication of this study is that while land use zoning of soils based on slopes is very essential in soil conservation, the incorporation of organic materials particularly in form of peat in steep arable slopes will greatly minimize soil erosion by water. It will also minimize surface runoff which will decrease the loss of nutrients from farmlands.

#### **5. References**


result is not always certain since it is always feared that greater surface runoff as a result of

The soil loss for the three soils with three levels of peat content compacted at three levels and exposed to four rainfall durations was used to generate a multiple linear regression

Student 't' (11.34) (-7.62) (- 4.43) (-3.69) (8.70)

(R = 0.878; N = 216) Where: SL is soil loss (kg); Ct is clay content of the soil (%); Pt is the peat content (%), Pc is compaction effort (kPa) and KE is raindrop kinetic energy (J m-2). R is the coefficient of multiple regression and N is the number of experimental data points. The signs of the experimental factors obtained confirm how the factors affected the soil loss. The R is significant at the 0.1% level. The student 't' values for all the experimental factors shown beneath them in the equation were all significant at 0.1% level. The relative 't' values for all the factors also confirm the findings in the analysis of variance which showed that the most important factors that affected soil loss were rainfall duration, soil type, compaction effort and peat content.

Soil loss by simulated rainfall was measured for three Trinidadian soils in the laboratory using a specially constructed soil erosion apparatus. Soil loss decreased with increasing peat content in all cases and was smallest in the clay loam soil and highest in the sandy loam. Peat decreased soil loss by decreasing runoff during rainfall. Soil loss declined with increasing compaction effort. The interactions involving rainfall duration showed that although soil erosion increases with rainfall duration, these increases will be reduced by increasing clay, and peat contents of the soil as well as the increasing level of soil compaction. A multiple regression equation derived to relate soil loss to the experimental factors was highly significant and confirmed that the most important factors that affected soil loss were rainfall duration, soil type, compaction effort and peat content. The implication of this study is that while land use zoning of soils based on slopes is very essential in soil conservation, the incorporation of organic materials particularly in form of peat in steep arable slopes will greatly minimize soil erosion by water. It will also minimize

ASTM 1985. Standard test method for moisture content penetration resistance relationships

Bjorneberg D L; Aase J K; Westermann D K (2000). Controlling sprinkler irrigation runoff,

of fine grained soils. Annual Book of American Society for Testing and Materials,

erosion and phosphorus loss with straw and polyacrylamide. Transactions of the

surface runoff which will decrease the loss of nutrients from farmlands.

SL = 0.767 - 0.00276 Ct 0.0307 Pt - 0.00386 Pc + 0.00172 KE (1)

**3.2 Derivation of regression equation relating soil loss to experimental factors** 

equation that could be used to predict soil loss. The equation was of the form:

soil compaction could increase soil erosion.

**4. Conclusion**

**5. References** 

04.08: 289 – 292.

ASAE 43: 1545 – 1551.


**10** 

*Austria* 

**Soil Erosion and Surface Runoff on** 

**Depending on Application Technique** 

**Slopes in Mountain Environment** 

**and Seed Mixture – A Case-Study** 

*Department of Ecological Restoration and Forage Crop Breeding* 

*Agricultural Research and Education Centre Raumberg-Gumpenstein, Irdning* 

Erosion is a basic problem found in the entire mountainous regions around the globe. Within the whole alpine area of Europe, thousands of hectares are affected every year, e.g. by construction of ski runs, ski lifts, tourists infrastructure and roads (CIPRA 1998). Besides, natural erosion causes increasingly more problems. According to estimates, 5,000 hectares have to be restored yearly following interventions in high altitudes, more than 50,000

High altitudes as the most sensible part of the Alps can be defined as areas within the prealpine and alpine belt i.e. areas above 1,600 msm in the Eastern Alps and areas above 1,800 msm in the Central Alps (Krautzer et al. 2006). Every disturbance in such alpine ecosystems leads to interference that requires different technical and ecological measurements. For lack of plant material in most cases, seed mixtures containing grasses and clover are normally used to establish vegetation again. Restoration of damaged areas in high altitudes is much too often done with an inadequate combination of technical and biological measurements. Cheap application techniques and cheap seed mixtures from species that are not adapted for high altitudes are state of the art. The resulting ecological and economical damage is considerable: soil erosion, extreme surface runoff, degradation of the vegetation, frequent reseeding, constant fertilising, flora falsification, expensive maintenance (Greif 1985, Bittermann 1993). Due to this situation, especially the economically important winter and

The research project "Seed Propagation of Indigenous Species and their Use for Restoration of Eroded Areas in the Alps" (FAIR CT98-4024, short title "Alperos"), supported by the EU, was dealing with the thematic to restore damaged areas using a combination of improved application techniques combined with seed mixtures of indigenous species. The goal of this project was to create a new state of the art in ecological restoration of damaged areas in high altitudes of the Alps. Results obtained during the four years 1999 to 2002 at 8 different locations in altitudes between 1,200 and 2,300 metres clearly showed multiple positive effects if indigenous sub-alpine and alpine species are used for restoration. Up to 20 %

hectares of insufficiently restored areas would need imperative improvement.

**1. Introduction** 

summer tourism got a very negative image.

Wilhelm Graiss and Bernhard Krautzer

