Comparison of German and Swiss Rainfall Simulators - Experimental Setup Kar1 Auerswald', Maximilian Kainzf, Dietmar Schröderu, W. Martin-

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Lehrstuhl für Bodenkunde, Technische Universität München, W-8050 Freising, FRG FB E I Abt. Bodenkunde, Postfach 3825, W-5500 Trier, ERG Bayerisches GeologischesLandesamt, Heßstr. 128, W-8000 München 40, FRG

Angenommen: 3 1. August 1991

Introduction Ariificial rainfall has been used for erosion studies in Germany for almost 100 years (Wollny, 1895). Several types of rainfall simulators have been developed since Wollny's time that try to reproduce natural erosive rainstorms. Comparability with natural rains is influenced not only by technical details, but also by the test procedures. Even amongst members of the German Society of Soil Science a number of very different procedures are used for erosion research. These were summarized by Auerswald et al. (1988). In order to examine the differences between rainfall simulators and typical applied procedures, all field rainfall simulator types currently used in Germany and Switzerland were simultaneously tested in a joint experiment by their staff. This is the first in a series of Papers describing the results of the comparison. It deals with the experimental conditions under which the 50 rainfall simulations were canied out.

Experimental site The rainfall simulations were conducted on an experimental farrn of the Technical University of Munich near Freising (Bavaria). The test plots were situated in the upper part Z. Pflanzenernähr. Bodenk.,155,l-5(1992)

of a straight NNE facing slope. The soil was a coarse silty, mixed Typic Hapludalf. A profile description is given in Table 1, and the mineralogical, chemical and physical characteristics in Tables 2-4. Table 1:Soil profile description Tabelle 1:Beschreibungdes Bodenprofils Coarse silty, mixed Typic Hapludalf PseudovergleyteParabraunerdeaus Lößlehmfließerde über tertiären TonJSand-Lagen Hor. Depth Description Ap 0 - 35 brown (10 YR 5/3) silt loam; fine subangular blocky; abrupt wavy boundary - 50 light yeuowish brown (10 YR 614) silty clay loam; Btl coarse subangular blocky; slightly mottled with common, small, soft Fe and Mn concretions; smooth diffuse boundary Bt2 - 100 yellowish brown (10YR 514) silty clay loam; weakly developed clay coatings; abundant, soft Fe and Mn concretions; many earthworm channels and common fine roots Soil type:

As the silt and very fine sand content exceeded 70 %, the K factor could not be calculated from the K factor equation. Its value of 0.56 t/ha . h/N was read from the K nornograph, adjusted to SI units by Schwertmann et al. (1987).

OVCH VerlagsgesellschaftmbH, W-6940 Weinheim, 1992

W-3263/92/0102-0001

$3.50 + 2510

Aiiersivald, Kainz, Schröder lind Martin

Field preparation

Table 2: Mineralogicai properties of the clay fraction Tabelle 2: Tonmineralzusammensetzung Hor.

Depth (cm)

S

AP Btl Bt2

0 - 35 - 50 - 100

16 32 48

V I (% of clay fraction) 21 15 9

K

53 48 38

10 5 5

Peak area determination of a glycerol-Ca-preparation was that X-rayed using Co-Ku radiation. Intensity comction factors: Smectite, 0.23; Vermiculite, 0.34; Illite, 1.0; Kaolinite, 0.24.

Rainfall simulators The comparison was conducted with five field rainfall simulators. Important characteristics and the utility of the simulators are compared by Kainz et al. (1992). One laboratory rainfall simulator (Auerswald et al., 1984) was also included in the experiment. It produces a narrow drop size distribution using hypodermic needles with rubber drop formers. The falling height of the drops is more than 14 m.

In 1988 the field used for the comparison was cropped with field peas. It was chiselled in August. Four days before the experiment started the soil was tilled to a 15 cm depth with a rotary harrow to produce an even, homogeneous surface with little organic Cover. Tilling direction was perpendicular to the slope. The tractor was equipped with 75 cm wide Terra-tyres. Aftenvards the field was consolidated slightly by a traveling wheel track beside the wheel track to reduce variations caused by wheel tracks. A second, 5 cm deep tillage was then performed up and down slope with the rotary harrow. Between the last tillage and the first experimental day several non-erosive rains of about 30 mm had fallen. This should have accelerated settling and stabilization of the soil after tillage without causing surface crusting. It can be assumed, that no relevant settling and stabilization occurred during the two experimental days that would bias the comparability of the results.

Table 3: Chemical properties of the soil at the test site Tabelle 3: Chemische Bodeneigenschaften Hor.

A P ~ AP2 Btl Bt2

Depth (cm)

Nt

0 - 15 - 35 - 50 - 100

0.13 0.11 0.05 0.03

Ci

PHC~CI~

(%I 1.05 1.07 0.30 0.20

CECpoi (cmolkg)

Na

12.1 11.7

1.5 3.9

7.O 6.8 6.4 5.4

K

Ca

Mg

89.9 85.4

4.0 5.1

(%I 4.8 5.6

Nt : Kjeldahl-extraction Ct: dry combustion with CSA 302 (ieybold Heraeus) pH. glass electrode exchangeable cations with 1 m NHeC1 at pH 7

Table 4: Physical properties of the soil at the test site Tabelle 4: Physikalische Bodeneigenschaften Pore size distribution (all measurements with 100 cm3 core samples): Porengrößenverteilung: Hor.

AP 1 Ap2 Btl Bt2

DePth km)

>I20

>50

5 - 12 25 - 32 40 - 47 60 - 67

8.2 5.7 3.7 1.1

10.6 8.6 6.7 3.1

Pore size dishibution (% v01.) 120-50 50-10 10-0.2 2.4 2.9 3.0 2.0

2.8 2.2 2.1 1.6