Finger test (soil)
The finger test is a method for determining the type of soil that can be used in pedological mapping without further aids .
Basics
The mineral soil is divided into coarse soil or soil skeleton with grain sizes over 2 mm and into fine soil with grain sizes up to 2 mm. The soil type names different mixtures of grain size proportions of the three grain fractions clay, silt and sand (or their respective sub-fractions) of the fine soil.
The finger test uses various physical properties of a moist soil sample to determine a soil type and speaks particularly the graininess that flouriness and the cohesiveness of a soil sample.
| Grain fraction | properties |
|---|---|
| volume | Easily malleable, sticky, cohesive, "dirty" and shows shiny sliding surfaces. |
| Silt | Moderately malleable, hardly cohesive, of a velvety, floury texture, does not "get dirty" and shows rough sliding surfaces. |
| sand | Not malleable, does not “dirty” and is grainy, both visible and tangible. |
| Clay | Contains all three grain fractions in different proportions. The dominant grain fraction determines its predominant characteristics. |
Requirements for using the method
- The soil sample has a uniformly moistened state, which can be produced by moistening it or by rubbing it dry between the fingers.
- Samples that are too dry are addressed in a slightly coarser manner, samples that are too wet with a slightly finer grain.
- The coarser and more angular the sand fraction, the easier it is to overestimate the proportion of sand.
- If the fine sand (grain size 0.063 mm to 0.125 mm) predominates in the soil sample and consists mainly of flaky particles such as mica, then the proportion of sand is often underestimated and the proportion of silt is overestimated.
- High carbonate proportions reduce the cohesion in clay-rich soils and can lead to an overestimation of the silt proportion.
- High humus contents can lead to an overestimation of the clay or silt content.
Reliable addressing of the soil types is only possible with sufficient experience. In order to sharpen and secure the feeling of addressing the finger sample, the results of the finger sample must be regularly compared with grain size analyzes from the laboratory or calibrated by repeatedly addressing standard samples examined by laboratory analysis.
Decision tree for determining the soil types based on DIN 19682-2
The following table is based on the soil type diagram contained in the Soil Science Mapping Instructions (see below). In each address, it is important to note which definition or which soil type diagram it is based on; In addition to this detailed form, there are also definitions of soil types in Germany based on soil assessment (Reich soil assessment) and various types of soil (Agricultural Investigation and Research Institutes (VDLUFA)); In Austria and Switzerland, however, different definitions are used and in the international (English) language area the soil type diagrams of the FAO, the USDA and the WRB.
| No | questions and answers | go to | ||
|---|---|---|---|---|
| 1 | A walnut-sized soil sample is to be formed into a ball between the palms of the hands and then rolled out into a thin roller about the thickness of a pencil | |||
| 1.1 | The floor cannot be rolled out, the roller crumbles before pencil strength is reached. This means that the main group of soil types, sand and silt, is almost clearly identified. |
2 | ||
| 1.2 | The floor can be rolled out, the roller is intact or only slightly cracked. With the exception of the silty loam Lu - the soil types of the main groups loam and clays are recognized. |
4th | ||
| 2 | Rub the soil between your thumb and forefinger and determine the degree of graininess | |||
| 2.1 | The soil is mostly grainy - rough. | 3 | ||
| 2.2 | The soil is predominantly velvety - floury. | 6th | ||
| 3 | Rub and roll the soil between the palms | |||
| 3.1 | The floor is very difficult to shape and it is impossible to roll it out The soil types of the main group of sands are thus clearly identified. |
5 | ||
| 3.2 | The floor is not very malleable and it is hardly possible to roll it out. | 6th | ||
| 4th | Rub the soil between your thumb and index finger, moisten a little if necessary, check for graininess and cohesion | |||
| 4.1 | The floor is a bit greasy - sticky, easy to shape and roll out, but cracked. | 7th | ||
| 4.2 | The floor is tough and sticky, has shiny sliding surfaces and grinds between the teeth. | 8th | ||
| 5 | Rub the floor dry between thumb and forefinger, check for roughness (the finer, the less rough) and fine content | |||
| 5.1 | Very little fine mineral substance adheres to the finger grooves. | 9.1 | ||
| 5.2 | Mineral, floury - dull fine substance adheres to the finger grooves. | 9.2 | ||
| 6th | Rub the bottom dry between your thumb and forefinger, roll it out about the thickness of a pencil | |||
| 6.1 | A lot of fine substance adheres to the finger grooves; the floor breaks and crumbles when you try to roll it out as thick as a pencil. | 9.3 | ||
| 6.2 | A lot of fine substance adheres to the finger grooves; the ground breaks even with a slight deformation. | 9.4 | ||
| 6.3 | The floor glistens in the sunlight, is difficult or impossible to shape, cannot be rolled out, but adheres well and is sticky. | 9.5 | ||
| 6.4 | The floor glistens in the sunlight, cannot be rolled out and is sticky, but adheres well and is rough - floury. | 9.6 | ||
| 6.5 | The floor is hardly malleable, tears and breaks very easily, but adheres well and is rough - floury | 9.7 | ||
| 6.6 | The soil is not malleable, cracks and breaks easily, adheres well and is velvety - floury | 9.8 | ||
| 7th | Rub and press the soil between thumb and forefinger, assess graininess and malleability | |||
| 7.1 | The bottom is very velvety - floury and a bit sticky, can be shaped and rolled out as thick as a pencil, but is cracked. | 9.9 | ||
| 7.2 | The floor is a little soapy - greasy, with a clearly noticeable grainy and rough sand content, can be shaped and rolled out as thick as a pencil, but cracked. | 9.10 | ||
| 7.3 | The bottom is sticky and slightly greasy, its floury receding, and when rubbed, a clear “sausage formation” becomes apparent. | 9.11 | ||
| 8th | Rub the soil with a little water between the thumb and forefinger and squeeze it, assess the sliding surfaces and check for graininess on the ear or between the teeth | |||
| 8.1 | The soil is grainy with a noticeable proportion of sand, with shiny to very shiny sliding surfaces, sticky. | 9.12 | ||
| 8.2 | The floor feels floury - velvety, the sand components recede completely, it is three-dimensional, can be shaped and rolled out and shows slightly shiny friction surfaces. | 9.13 | ||
| 8.3 | The floor is tough and sticky; distinct grinding audible or noticeable between the teeth; it shows shiny friction surfaces. | 9.14 | ||
| 8.4 | The bottom is buttery soft and sticky, there is little or no grinding noticeable between the teeth; it shows shiny friction surfaces. | 9.15 | ||
| 9.1 | Little or no fine substance adheres to the finger grooves. | Ss | ss | s |
| 9.2 | Grains of sand are clearly visible and palpable; very little fine substance adheres to the finger grooves. | Su2 | ls | s |
| Sand, clearly containing fine substance; In the finger grooves weakly floury adheres fine substance. | Su3 | us | s | |
| Sand with a lot of fine substance; In the finger grooves, there is a strong floury fine substance. | Su4 | us | s | |
| 9.3 | Grains of sand are clearly visible and; Little fine substance adheres to the finger grooves. | Sl2 | ls | s |
| Grains of sand clearly visible and palpable; Little to moderately fine substance adheres to the finger grooves. | Sl3 | ls | s | |
| Grains of sand are clearly visible and palpable with moderate to high levels of fine substance. | Sl4 | sl | l | |
| Grains of sand clearly visible and palpable; clearly floury due to a lot of fine substance. | Slu | sl | l | |
| 9.4 | Grains of sand are clearly visible and palpable, despite being only moderately fine, very sticky (“honey sand”). | St3 | sl | l |
| Grains of sand can be seen and felt; very little fine substance adheres to the finger grooves. | St2 | ls | s | |
| 9.5 | Grains of sand are barely or not visible and palpable; the velvety floury fine substance clearly adheres to finger grooves; the friction surface is matt and flaky. | Uu | see below | u |
| 9.6 | Grains of sand can be seen and felt; velvety-floury fine substance clearly adheres to finger grooves; the friction surface is grainy, matt and flaky. | Us | see below | u |
| 9.7 | Grains of sand can be seen and felt; the predominantly slightly floury fine substance clearly adheres to finger grooves. | Uls | lu | u |
| 9.8 | Grains of sand are barely or not visible and palpable; the very mealy fine substance adheres clearly to finger grooves and forms a rough, matt and flaky friction surface. | Ut2 | lu | u |
| No grains of sand visible or palpable; the clearly floury fine substance adheres clearly to finger grooves; the friction surface is matt and flaky. | Ut3 | lu | u | |
| No grains of sand visible or palpable; the slightly floury fine substance adheres and sticks somewhat and forms a matt to slightly shiny, flaky friction surface. | Ut4 | do | u | |
| 9.9 | Grains of sand are not or barely visible and can only be felt weakly; a lot of cohesive fine substance forms a rough, matt to slightly shiny, granular and flaky friction surface. | Lu | do | u |
| 9.10 | Grains of sand are clearly visible and palpable; very slightly floury with a lot of fine substance. | Ls2 | ll | l |
| Grains of sand are clearly visible and tangible, with a lot of fine substance, shiny friction surface and very clearly grainy. | Bs3 | ll | l | |
| Grains of sand are clearly visible and palpable; only moderately fine substance, there
slightly shiny friction surface and very clearly grainy. |
Bs4 | ll | l | |
| 9.11 | Grains of sand are clearly visible and palpable, a lot of fine substance and a slightly rough, slightly shiny friction surface. | Lt2 | ll | l |
| Grains of sand are clearly visible and tangible, rich in fine substance with a very shiny, granular friction surface. | Lts | tl | l | |
| Grains of sand can be seen and felt, due to the large amount of fine substance, viscoplastic with a slightly rough, slightly granular, shiny friction surface. | Lt3 | ut | t | |
| 9.12 | Few grains of sand visible and palpable, rich in fine substance with a very shiny friction surface. | Ts2 | according to | t |
| Grains of sand are clearly visible and tangible, a lot of fine substance with a slightly rough, shiny, clearly granular friction surface. | Ts3 | tl | l | |
| Grains of sand are clearly visible and palpable, a lot of fine substance with a rough, shiny, clearly grainy friction surface. | Ts4 | tl | l | |
| 9.13 | No grains of sand visible or palpable; the fine substance forms a rough, slightly shiny friction surface. | Tu4 | ut | t |
| No grains of sand visible or palpable; The tough plastic fine substance forms a slightly rough, shiny friction surface. | Tu3 | ut | t | |
| No grains of sand visible or palpable; the highly plastic fine substance forms a slightly rough, shiny friction surface. | Tu2 | according to | t | |
| 9.14 | Very few grains of sand can be seen and felt, a great deal of tough plastic fine substance with a shiny friction surface. | Tl | according to | t |
| 9.15 | No grains of sand visible or palpable; the highly plastic, fine substance that can be rolled out as thin as a millimeter forms a smooth, slightly shiny to shiny friction surface. | Tt | according to | t |
Figure 1: Soil type diagram Soil mapping instructions
Table 2: Designation of the soil type groups and main soil type groups
| Soil type group | Soil types main group | ||
|---|---|---|---|
| ss | Pure sand | ||
| us | Silt sands | s | Sands |
| ls | Clay sands | ||
| sl | Sand-loam | ||
| ll | Loam-loam | l | Clay |
| tl | Clay loam | ||
| see below | Sand silts | ||
| lu | Clay silt | u | Silt |
| do | Clay silts | ||
| ut | Silt clays | t | Clays |
| according to | Clay clays |
literature
- DIN 19682-2: 2007-11 - Soil quality - Field investigations - Part 2: Determination of the soil type
Web links
Wikiversity: Soil Science Institute - course materials
