Tropeano-1984-Earth_Surface_Processes_and_Landforms

geonerd

Tropeano-1984-Earth_Surface_Processes_and_Landforms

EARTH SURFACE PROCESSES AND LANDFORMS, VOL. 9,253266 (1984)

RATE OF SOIL EROSION PROCESSES ON VINEYARDS IN

CENTRAL PIEDMONT (NW ITALY)

WMENICO TROPEANO

C.N.R. Istituto di ricercaper la Protezione Idrogeologica nel Bacino Padano, Via Vassalli Eandi 18, 10138 Torino, Italy

Received 16 February 1983

Revised 20 October 1983

ABSTRACT

The ‘Tertiary Basin of Piedmont’ is a hilly region, mainly composed of marine sediments, such as marls, silts and sands. The

slopes, largely devoted to grape production, are usually kept bare of vegetation and are thus prone to soil erosion processes.

For two years we have measured soil loss in relation to rainfall on experimental plots located in vineyards. In all the plots

considered erosion started with low rainfall intensities (0.07 mm/min), and above 0.4 mm/min the amount of soil loss

dramatically increased (to over 1800 g/m in one event). Most of the erosion occurs during summer rainstorms, but the

behaviour of the soil under erosive rainfalls is very different from one site to another, depending only in part upon the

various rainfall rates, soil and geometrical characteristics of the plots. It can be seen that soil loss varies from nearly

negligible values (20 g/m/yr) to unacceptably high levels (to over 4-7 kg/m/yr), according to the different types of land

cultivation. Deep ploughing and heavy herbicide treatment give rise to accelerated erosion processes leading to soil losses

much higher than in other vineyard plots in Europe.

KEY WORDS Soil erosion Experimental areas Cultivated lands Northwestern Itdy

INTRODUCTION

Published data on the quantitative relationship between natural rainfall and soil erosion in Italy as a function

of different agricultural land uses have been available since the early 1970s (Chisci and Tellini, 1974; Chisci,

1976 Boschi and Chisci, 1978; Zanchi, 1981 and others). From an experimental point of view, the effects of

rainfall-induced erosion on vine-cultivated hillslopes have not been, up to the present, taken into account. In

most vineyards of Central Piedmont, as a rule, the soil is artificially kept bare of plants, thus slopes occupied by

vineyards currently prove to be more prone to erosional processes than those cultivated with other crops.

On the hilly slopes of Piedmont, the grape cultivation extends over an area of 963 km2 (Istituto Centrale di

Statistica, 1980), thus representing a major support to the rural economy of the region. Nevertheless, the

problem of soil erosion, though important, is still poorly understood by the vine-growers, the crop being

remunerative enough to make up for timeconsuming restorations of the rows occasionally damaged. On the

other hand, in some cases there is a tendency to practice the up- and downhill tillage technique, instead of the

traditional work along contours, in order to facilitate runoff. Some farmers prefer to risk gullying rather than

the mass movements downslope induced by excess of infiltration into the soil.

Data recorded during 1981 in the experimental areas under survey by the C.N.R. ‘Istituto per la Protezione

Idrogeologica nel Bacino Padano’ showed that, during single rainstorms, erosion in such areas was much

greater than reported in the European literature for similar experimental vineyard areas (Tropeano, 1983). In

the last 30 years mechanized agricultural equipment has increasingly replaced manual work in land cultivation.

01 97-9337/84/03025 3-14$0 1.40

0 1984 by John Wiley & Sons, Ltd.


254 D. TROPEANO

There is no doubt that the growing mechanization has led to accelerated erosion on the already lithologically

weak terrain found throughout the hilly slopes of Central Piedmont.

From a geological point of view, the area considered here (Figure 1) forms part of a larger region named

‘Tertiary Piedmontese Basin’, which was occupied by the sea until the end of Pliocene. The area is mostly

composed of unconsolidated, coarse to fine grained sediments, ranging in age from Oligocene to the late

Pliocene, arranged, on the whole, in a gentle syncline from North to South. In Figure 1 four elements of the

landscape may be singled out: (a) the Turin hills, above, mainly composed by Lower and Middle Miocene

sediments, with silty marls widespread with sands and conglomerates also present; (b) the Monferrato hills, in

the centre right, here mainly corresponding to Pliocene deposits of silt and fine sands; (c) the borders of the

Langhe area, in the southernmost part, where marls and clays of Upper Miocene and Lower Pliocene prevail;

(d) the alluvial plateau, to the west, built by Quaternary deposits of silt, sand and gravel. These deposits

formerly extended over large part of the River Tanaro valley, overlying the Pliocene sediments, but

subsequently were removed by stream erosion, leaving the remnants on the topmost of the hills.

1

Figure 1. Geologic sketch of the study area, and location of the experimental sites: (1) Miocene, (2) Pliocene, (3) Quaternary; (A)

Albugnano, (M) Mongardino, (C) Cinzano, near S. Vittoria d’Alba


SOIL EROSION PROCESSES 255

EXPERIMENTAL SITES

In the region described above, and in the Winter 1980-8 1 three vineyard areas were equipped as study sites. The

first lies near Albugnano (Figure l), in the experimental area of C.N.R. Istituto per la Meccanizzazione

Agricola, on mark with rare thin sandstone beds, belonging to the Baldissero Formation. The second, near

Mongardino, is a privately-owned vineyard, on silt and fine sands at the base of the ‘Sabbie di Asti’ Formation.

The last one belongs to the wine-producing factory ‘Cinzano S.p.A.’, near S. Vittoria d’Alba with silty-clayey

marl outcrops, at the junction of Miocene-Pliocene.

In all three vineyards the soil may be classified as eutrochrepts, according to the definition of Soil Taxonomy

(U.S.D.A., 1975). The physical characteristics of the areas (Table I) have been described elsewhere (Tropeano,

1983). Although some characteristics, in particular soil particle size and slope angle, vary from one site to

another, the main difference between the three study sites lies in the manner of cultivation. At Albugnano the

slope was first deeply ploughed (down to 1 m) up- and downhill just before the start of the surveys. Then

followed other cultivation, such as rotovating, uprooting, tillage, mulching, borings for plant vines and

support-stakes, until October 1981. The only subsequent soil disturbance was in the first half of 1982 when

tractors were used to spread compost and cut weeds. At Mongardino vines were planted manually in the early

1950s and then every other year the soil was machine tilled. At S. Vittoria d’Alba the vineyard was planted

manually in 1967 and only occasional digging was then carried out. However, over the whole survey period

only herbicides were employed at Mongardino and drying agents at S. Vittoria and no tillage was used.

At the test sites the rows are orientated across slope, as in most of the Piedmontese vineyards. The need arose

therefore to select stretches of land set at even slopes so arranged as to avoid runoff diversions. No lateral

boundaries were placed, lest they gave rise to forced runoff effects and interfered with farming operations. The

upper boundaries were edges of drainage tracks (Albugnano and S. Vittoria) or a natural divide (Mongardino).

At Albugnano, three plots of similar slope and length were selected, so that in processing the data only an

average value could be taken into account. At Mongardino, since 14 April 1982 there were two plots of similar

characteristics, and at S. Vittoria only individual plots were considered (Figure 2).

Field apparatus

Rainfall was measured by a tipping-bucket, autographic gauge SIAP in all sites and by two additional

raingauges both at Mongardino and S. Vittoria. Runoff and sediments were trapped by I-m wide galvanized

troughs,cascade-connected with 120-1 drums (Plots A 1-3, M 2, C 1-2-3) or measured by tipping bucket devices.

These were purposely designed to measure total runoff (Plot M 1) or for continuous recording on a magnetic

tape (Plot A 2), while at the same time a steady portion of the whole runoff-sediment mixture was sampled

(Figure 3).

Table I. Characteristics of the experimental areas

Mean

Locality Elevation yearly

rainfall

(m a.s.f.) (mm)

Albugnano 450 862

Mongardino 175 639

S. Vittoria 210 734

d‘Alba

Soil particle size

Sand Silt Clay

(%I (%) (%I

30 48 22

9 73 18

13 59 28

Plot Length Slope Aspect

Vegetative cover

lstyr

2ndyr

A1-2-3 30* 36 South Absent Diffuse

M 1-2 31 31 West Absent Absent

c1 29

c 2 44 :i ] South Diffuse Diffuse

c3 58 40

*The soil surface was covered by 9 strips of plastic film mulches, horizontals, 0 5 m wide, equally spaced. Thus, the actual length of slope

exposed to erosion should be considered as 255 m.


256 D. TROPEANO

DATA PROCESSING AND RESULTS

Surveys were made simultaneously at the three sites, between February 1981 and December 1982, following the

rain periods. Plots were sampled, and collected sediments were ovendried and weighed everytime. On the

whole, 140 rainfall events in all sites were identified, together with the relevant runoff and soil loss data. These

numerous data were used in a statistical analysis to make up for the relatively short period of survey. Different

values of cumulative rainfall, peak intensities, total erosive rains and duration of cumulative rainfall were

derived from the rainfall records, and pluviometric parameters were compared with runoff and sediment yield.

The data were processed in the light of four main objectives:

1. To establish the threshold values above which erosion processes start.

2. To determine the range of soil erosion intensities.

3. To estimate the amount of yearly soil loss.

4. To work out empirical formulae for predicting the rate of soil erosion based on given hydrological

characteristics.

The results attained should be reasonably applicable to any areas with physical and environmental

conditions similar to the ones of the plots under survey.

In all three areas it was generally observed that an appreciable amount of sediment yield occurred (of the

order of 5-20 g collected in the troughs) even under the effects of low rainfall intensities (0.07408 mm/min).

However, a more consistent sediment transport took place for slightly higher rainfall intensities, and for

practical purposes the value of 0.12 mm/min was assumed as the lower limit to define rainfall as ‘erosive’.

On the basis of the data collected, two kinds of erosion may be singled out (Table 11): the first one could be

called current erosion and the other mere erosion. The lower limit of rainfall intensity likely to cause severe

erosion may be fixed in all the areas at 0-4 mm/min and the higher peak intensity recorded was around

1.5 mm/min (29 out of the 140 rainfall events recorded lie in this range of erosion). While the average value of

soil loss was very low in the previous range, in this latter condition it rose suddenly to quite considerable values,

with peaks of 1600-1800 g/m and probably more. In Table I11 some of the most significant data relating to

experimental areas are reported, taking into account only the events with peak intensities equal to, or above,

a


SOIL EROSION PROCESSES 257

Figure 2. The study sites of Albugnano at the beginning of the surveys (a), Mongardino (b) and S. Vittljria d’Alba (c) showing the

traditional orientation of the rows across slope. The arrows mark the location of the traps


258 D. TROPEANO

Figure 3. A runoff guage: (A) in!et hose, (B) bucket, @?-litre capacity, (C) sampling slit, (D) pivotconnected rod, (E) electro-magnetic

contact

Table 11. Current erosion and severe erosion values (underlined) in

the experimental sites

Suspended

Range of peak solids Soil loss

Area intensity of

rainfalls Duration

concentr. (g/l) (g/m)

(mm/min) (min) average extr. aver. extr.

Al bugnano

Mongardino

S. Vittoria

0.08-0.40 15-30 16 150 2 50

-- 0.40-144 - 15 - 88 2300 21800

0.07-0.40 15-60 20 150 13 200

0.40-1.24 115 2 0 0 - 243 21600

0.07440 1&30 12 55 1 25

25 - 150

@B -

15 49 -

04 mm/min; such events frequently occur in the area under survey. During 1981-1982 we recorded 34 showers

(57 per cent of which equalled or exceeded 0 4 mm/min)at Albugnano, 30at Mongardino (60 per cent of which

equalled or exceeded 0-4mm/min) and 23 at S. Vittoria (43 per cent of which equalled or exceeded

04 mm/min). For the showers which proved particularly effective in causing erosion, a lower limit of 0.18

mm/min may be fixed, above which threshold rainfalls are herein defined as ‘intense’. Such events are

summarized in Table IV, together with the total rainfalls during which they occurred. It can be seen from this

Table that practically all soil loss is due to such events of short duration.


Table 111. Storm events and related soil loss in the survey period (22 months)

Albugnano (Plots A 1-2-3 combined) Mongardino (Plot M 1) S. Vittoria d'Alba (Plot C 3)

Peak Soil Peak Soil Peak Soil

Date Rainfall intens. loss Date Rainfall intens. loss Date

Rainfall intens. loss v1

(mm) (-/min) Wm) (mm) (mm/min) (dm) (-1 (-/mi4 (dm) 8

16 May 1981 24.0 093 1492 13 July 1981 368 1.00 182 16-28 June 1981 74.0 040 70 g

26-27 May 1981 54.0 0.43 997 17 July 1981 21.0 1.20 692 7 Aug. 1981 25.8 0.83 800

22-28 June 1981 1W3 0.77 1282 9 Aug. 1981 42.6 1.17 21613(*' 11 Aug. 1981

27.6 0.45 151.0 8

2-3 July 1981 19.6 0.38 580 17 Aug. 1981 26.2 1.00 322 5 June 1982 160 0.40 0 2

18 July 1981 46.0 0.75 2 18W*) 10 Sep. 1981 33.0 066 188 26 June 1982 23.2 1.49 18.0

11 Aug. 1981 41.5 0-66 344 17 July 1982 26.6 073 332 23 July 1982 44.6 0.95 24.0

17 Aug. 1981 23.6 0.58 205 23 July 1982 27.4 040 197 6 Aug. 1982 13.0 0.46 04 g

31 Aug. 1982 24.6 1-44 519 24 July 1982 19.0 074 432 5 Sep. 1982 8.2 018 1.7

6-7 Sep. 1982 36.6 0.80 506 6-17 Aug. 1982 27.0 1.00 266

20-28 Aug. 1982 31.2 0.75 587

31 Aug. 1982 276 071 592

24-25 Sep. 1982 18.8 1.24 277

(*) Actual data unknown, because both traps and drums were filled totally by water and sediments.


~

260

D. TROPEANO

Table IV. Summary of the intense rainfalls in the study area

Plot Rainfall depths Number

(% of yearly total) of showers

1981 1982 1981 1982

A 1-2-3 52.7 10.7 19 15

M1 60.0 33.8 15 15

Ei 63.6 28.1 13 10

c3

Mean intensity

of the showers

(mm/min)

1981 1982

043 0.59

050 0.60

037 0.56

Intense Soil loss

rainfalls (% of yearly

(mm) total)

1981 1982 1981 1982

180 162 96.1 93.6

191 144 99.2 94.1

97.5 20.1

loo 105 { 89.7 735

98.1 84.4

Figure 4, derived from Tables IV and V, compares the three areas in terms of susceptibility to erosion.

Factors were introduced to make the rainfalls in the areas under consideration easily comparable. It seemed

suitable to combine such factors in the ratio S,L/R, x I,, where: S,L is the total soil loss per unit of length

(g/m); Ri is the total depth of the intense rainfall in the year (mm); and, I, is the mean intensity of the showers

during which such rains fell.

The estimate of soil loss in the two years of survey is summarized in Table V. Generally speaking, soil loss in

1982 was lower than in 1981 even though the total rainfall was equal or even higher. The most remarkable

differences are evident for Plots A 1-2-3 and C 3. The reason will be explained later (see Discussion and

Conclusions).

The multiple regression method was applied as the final step in data processing. Rainfall events recognized as

more significant from the point of view of rainfall/erosion response (80 in total) were selected. The dependent

variables ‘eroded materials’ and ‘runoff’ were combined separately for each plot with the following

hydrological parameters:

-cumulative rainfall (mm);

-peak intensity (mm/min);

-erosive rainfall (mm);

-duration of cumulative rainfall (min);

-mean rainfall intensity (mm/min).

80 -

60 -

0 1981

1 1982

40 -

20 -

0-

Albugnano

Mongardino

EkuJ

S. Vittoria

d’ Alba

Figure 4. Soil loss values, as a function of yearly amount of the intense rainfalls. Numbers on scale refer to the ratio S,L/Ri x I , (for

explanation of symbols see text)


SOIL EROSION PROCESSES 261

Table V. Summary of rainfalls and soil loss rate in the study area

Plot Cumulative rainfalls Total erosive Total soil loss Yearly

(mm) (*I rainfalls (%) (kg) soil loss

1981 1982 1981 1982 1981 1982 (kg/m)

A 1-2-3 723 720 27 24 249.10 35-42 4.74

M1 605 679 44 26 100.92 87-15 3.03

0.94 0-13 0.02

} 428 662 27 19 { 3.45 3.07 0.07

15.86 3.32 0-16

c3

(*)Snowfall excluded, not inducing erosion.

As a whole the parameters most closely correlated with the dependent variables are cumulative rainfall (R,)

and peak intensity (I). Slight improvements in the correlation between rainfalls and soil loss were obtained, in

all cases except in Plots A 1-2-3, by adding the erosive rainfall parameter (Re) to the above parameters. The

results of analytical processing are summarized in Table VI.

DISCUSSION

Analytical comparisons between the various parameters may be grouped in three orders (Table VI). The first

shows only intermediate-to-definite rainfall-runoff correlations (r = 0.65 to r = 0.70) in all plots except C 1,

where the correlation is satisfactory (r = 0.85). Rainfall-soil loss correlations appear in second place, showing

in general a slight improvement (from r = 0.67 to r = 0.83). Then, soil loss and runoff are characterized by a

very close relationship (ranging from r = 0.94 to r = 0.98) in all plots except A 1-2-3 where the correlation is

not as good (r = 0.85).

Bearing in mind the above results, it will be easily seen that the same lithological nature of the rock surface in

all plots, consisting of loose and fine grained particles, justifies the very strong correlation between amount of

runoff and soil losses. The greater the depth of the overland flow, the greater the tendency of the soil to be

washed away. Without discussing here the problem of the interaction between raindrop energy and surface

flow in producing soil loss (see considerations expressed by several authors, in Thornes, 1976, pp. 22-24), we

simply infer that, as a final result, runoff rather than raindrop impact plays a basic role in erosional processes in

our study sites.

The lower correlation coefficients in the rainfall-runoff and rainfall-soil loss combinations are probably due

to the strong influence of incidental variables, which is very difficult to evaluate quantitatively and is therefore

not included in the multiple correlation parameters. One of the most important incidental variables to be

identified is the difference between the rainfall recorded at the raingauge and the actual rainfall measured near

the soil surface between the rows; here screening effects may occur, produced by the vine foliage, on rains

accompanied by wind.

To verify the extent of such difference on 17 rainfall events in Summer and Autumn 1982, both the recorded

values and those supplied by four raingauges at Mongardino and S. Vittoria were compared. In the first site,

the mean error was 4.09 and 4.61 per cent of the corresponding recorded values. In the other, it was higher at

6.73 and 7.28 per cent of the recorded values. The total difference, however, was considerably smaller, and in the

two sites mentioned was 16-1.8 and 0.7-1.8 per cent, respectively, of the corresponding total rainfall depths

recorded. We may infer that the magnitude of difference reported here is not such as to strongly affect the

quality of multiple correlations.

Another and undoubtedly even more important factor expressing erosional processes is the occurrence of

preferential flow lines, which concentrate in rills or small gullies. In periods between one erosional event and

the next, the soil surface is likely to be changed by biological activity, farming operations and so on. During

rainfall, this will result in a new arrangement of the flow lines, with obvious changes in the amount of sediment


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SOIL EROSION PROCESSES 263

transported. In the course of heavy rainfall (which often occurred in the area under control see Table 111) quick

deepening or widening of rills, piping phenomena, etc. may produce an excess of erosion or mass movement

processes on a small scale. It is evident, in this case, that the correlation between soil loss and rainfall

characteristics is not immediate.

Abnormal erosion rates in Plots A 1-2-3 and C 3 during 1981 can be explained only by taking into account

the occurrence of erosional processes like those detailed above. In the period from May to December 1982, a

second plot was studied near and parallel to the first one at Mongardino, on a slope apparently in the same

physical conditions. Nevertheless, the total amount of sediments collected exceeded by 21.7 per cent the

quantity trapped in the same period at the outlet of the previous plot. Also, in this case the incidence of

fortuitous variables had been strong. At Albugnano, since the beginning, soil losses and runoff had been

measured separately for the three physically homogeneous plots, lying on the same stretch of slope. The total

difference between the maximum and minimum value, over the entire survey period, was 32.7 per cent of the

maximum value. Such difference may be understood if we consider that vegetative cover (grass and weeds) in

the second year developed over the whole surface, though somehow more abundantly on the less eroded plot.

In addition, there is no doubt that the propensity of a soil to be eroded is variously affected by farming

practices-such as ploughing, tillage, and the use of plastic film mulches-and may vary greatly, not only from

one place to another, but also within the same plot.

The results of analytical comparisons suggest that the best forecast of soil loss can be obtained by direct

measurements of runoff. The expected amount of sediments, in each individual event, may be computed by

making use of the regression equations reported in Table VI.3.

Based on the data collected in the survey period, we observed that almost all erosive activity in the study area

was concentrated in the warm months, being strongly affected by showers (Table IV). Although the total depth

of such rains is slight if compared to the total annual rainfall depth, parameters such as ‘intense rainfalls’ and

their mean intensity prove to be highly significant. In fact, Figure 4 shows that the intense rainfall-soil loss

relationship remained quite uniform over the two years in the Mongardino area-the most important in this

context. The Albugnano area is an exception inasmuch as basic changes occurred in land treatment and

vegetative cover from 1981 to 1982.

Soil humidity before a storm is an important parameter controlling the start of overland flow. No

measurements of this variable, neither on the infiltration into the slopes, were made; however, in the intervals

between rainy periods in the warm season it was always observed that the soil surface quickly dried in all three

areas, subjected to strong insolation and high temperatures. In this respect, the data recorded by the C.N.R.

Istituto per la Meccanivazione Agricola at Albugnano are significant. During 1981, in the warmest season

(from 1 June to 31 August) the mean value of the maximum daily temperature was of about 26°C with a

minimum average air moisture of 59 per cent. In the same period, in 1982, the same daily values were 27°C and

58 per cent respectively. Under such conditions it can easily be seen that the soil surface may be considered in an

almost steady state of dryness from one storm to another, in the very period when erosion is most important.

CONCLUSIONS

The rainfall depths for each month of the two-year survey (as compared with the mean monthly values

supplied by a long series of pluviometric surveys at stations very close to the sites under study), and the runoff

and soil loss data (Figure 5) show that the sites differ markedly from one another in both runoff and soil loss

values. Such differences can only be explained by taking into account the different cultivation techniques in the

three areas.

At Albugnano, in the first year a sequence of fully-mechanized operations led the soil to an excessive

weakness and to an increased seepage capacity, while the surface was kept bare of vegetation. This resulted in

abnormal erosion values and relatively low runoff. In the second year, no tillage or herbicide treatment was

made and the vegetative cover established itself widely. Keeping in mind the slight difference in total rainfall

depths between 1981 and 1982, we observed (Table V) that after only one year soil losses were reduced to less

than 1/7 of their former values.

At Mongardino, where no tillage was carried out but full herbicide treatment was made in the course of the


D. TROPEANO

ALBUGNANO

-8

1982

-6

200-

-4

100-

-2

0-

-0

MONGARDINO

n

10 -2.0

8 -

- 1.5

1981 1982

6 -

4 -

- 1.0

Ino1 0

0 t 0

100

1981

S. VlTTORlA D'ALBA

0

J F M A M J J A S O N D

J F M A M J J A S O N D Z

0

>

1 Monthly rainfall 1981-1982 -. / Runoff soil loss W

7 Average monthly rainfall -.,-' Runoff (Plot C21 0

Figure 5. Monthly values of rainfall, runoff and soil loss in the experimental areas. There is probably a lack of runoff (and consequently

soil 1oss)data in 1981 at Albugnano (July)and Mongardino (August), owing to thecomplete filling of both traps anddrums. Runoff of Plot

C 1 is not reported, it being too low

._ ui


SOIL EROSION PROCESSES 265

Table VII. Soil loss values recorded in some plots in European vineyards

Locality

Field characteristics

Date and rainfall values

Soil loss

Bergheim, Alsace

(Messer, 1980)

Mertesdorf, Moselle

Valley (Richter,

1980)

Tokaj, Hungary

(Pinczks, 1980)

clayey silt

(36% clay, 52% silt, 12% sand)

slope inclination 21 %

plot size 3.40 x 20m

rigosol of weathered slate

(40% coarse material, 30%

sand, 20% silt, 10% clay)

slope inclination 37 %

plot size 2 x 32m

loess

slope inclination 32.5 %

plot size 5 x 70 m

from 10 Jan. 1977 to 3 Jan. 1978

574 mm (peak intensities between

20 and 30 mm/h seldom occurred)

from Nov. 1974 to Oct. 1977

1583 mm (peak intensities

between 1.0 and 8.4 mm in 10)

13 Aug. 1964

22.8 mm in 1.5

2700 g

3800 g

519 dm’

year, soil losses were much larger, owing to a greater amount of runoff. Piping processes are widespread in this

vineyard, which is totally unprotected by a vegetative mantle, as in many vineyards of the surrounding area.

At S. Vittoria problems of soil degradation practically do not exist, one plot only (C 3) being weakly eroded.

During the survey period no tillage or herbicide treatment was made, but once a year drying agents were

employed. In this way, the grass cover was thinned out, but not destroyed, and in addition vine-shoots were laid

down inter-rows. Although soil loss tends to increase with the length of plots (Table V), we observed that soil

erosion at S. Vittoria was kept within narrow limits, while in the other two sites it was much heavier.

It should be noted from Figure 5, that in the period when erosion was more severe, i.e. in Summer, monthly

rainfall totals were not too different from the average values either at Albugnano or at S. Vittoria, whereas at

Mongardino they were markedly higher. In any case, if the present rate of surface denudation persists in the

study area (e.g. 2.3 mm/yr at Mongardino, where the average bulk density of the soil is 1.3), we may observe the

strong influence of man’s impact on short term geomorphic processes eroding the slopes of cultivated lands in

Central Piedmont.

Soil loss data collected in the two years of measurements confirms what has already been said; that is, slope

erosion in our plots appear by far heavier than in other vineyards in Europe. A rough comparison, although

rainfall and soil characteristics are not the same, can be made between data presented in Table V and Table VII.

Soil loss values reported by Messer, 1980 and Richter, 1980 may be converted in 40 g/m2 and 20 g/m2 in a

year, respectively, vs. over 4700g/m2 and 3000g/m2 in the most eroded plots in study (Albugnano and

Mongardino), assuming that the traps refer to an area of the same wideness (1 m). No yearly soil loss data, but

the maximum amount of soil loss in ten years for one event has been supplied by Pinczes, 1980 it was about

, 1140 g/mz, if we assume a bulk density of 1.3. Also in this case such value, compared with some of these

presented in Table 111, was overcome more than once in our experimental areas.

ACKNOWLEDGEMENTS

This research has been carried out with the cooperation of staff members of the C.N.R. Istituto per la

Protezione Idrogeologica: E. Viola (periodic field surveys), F. Godone (instrument management), G. M.

Caiazzo (mechanical design), P. G. Trebo’ (additional jobs); E. Caroni performed the data processing and

planned the runoff gauges.

A lot of helpful contributions was given by Mr. S. Parena, staff member of C.N.R. Istituto per la

Meccanivazione Agricola. Thanks are also due to Mr. E. Bosco, of Mongardino, and to Mr. V. Paganelli, of

‘Cinzano S. p. A.’, who kindly allowed free admittance to their vineyards.

The author is gratefully indebted to Prof. L. Starkel, of the Polish Academy of Sciences, for the helpful

remarks and suggestions on some problems arising from the present research.


266 D. TROPEANO

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