Soil investigation
The collective term soil investigation is understood to mean the summary of various methods and procedures for determining soil parameters such as nutrient and humus content , soil organisms , properties of the water and air balance , pressure sensitivity and physical composition ( grain size distribution ). The investigation generally begins with taking a soil sample .
Taking the sample
A representative sampling is a basic requirement for a meaningful soil investigation. Sampling instructions are published by the Association of German Agricultural Testing and Research Institutes (VDLUFA) for nutrient analysis in agriculture . A distinction is made between sampling for basic nutrient analyzes and for analyzes of plant-available nitrogen.
The soil sample is taken from a uniform area as part of a sampling for a soil investigation. It is common to form a mixed sample of around 0.2 kg to 0.5 kg of soil, which is obtained from around 20 individual samples.
Sampling for basic nutrient analysis
On arable land , at least 15 punctures at the working depth (see plowing ) are required, on grassland at least 20 punctures up to 10 cm deep. In the case of hops , orchards and viticulture, at least 15 punctures to a depth of 30 cm should be made. For certain questions ( grape wilt , stalk paralysis ) in viticulture, an examination of the subsoil (30 to 60 cm deep) is also useful. The individual samples should be taken evenly over the area in the main root area. A simple hand boring stick with a footrest is suitable as a removal device . The individual drill cores are well mixed and homogenized in a bucket. A partial sample of around 200 grams is placed in a plastic bag and sent to a soil laboratory.
The same soil sample that was taken for the basic nutrient analysis can also be used to determine the humus content. The humus content allows conclusions to be drawn about the organic matter in the soil. The laboratory-analytical measurement of the humus content is prescribed within the framework of cross compliance under certain conditions.
Sampling for analyzes of plant-available nitrogen ( Nmin )
Since the mineral nitrogen in the soil is very mobile, the samples are taken from a depth of up to 90 cm. A Pürckhauer with a mallet is suitable for this. Mechanical removal with an electric hammer is much more convenient. Soil samples that are to be examined for mineral nitrogen must be taken to a testing laboratory or frozen immediately after they have been taken. Otherwise there will be an increase in the nitrate content and the analytical result is no longer meaningful.
The soil samples are mixed well after they have been taken and prepared for transport. If the mineralization status of the nutrients is to be determined, it is necessary to deep-freeze the sample for transport. Further evaluation takes place in the laboratory. For this purpose, the samples are dried at 105 ° C. For the soil analysis, the fine soil is sieved out (mesh size 2 mm). The plant-available nutrient content of the fine soil is obtained from the sample with various extraction agents and determined with the help of various analysis devices.
Analyzes
Fertilizer requirement
A number of parameters to be examined are specified in the Fertilizer Ordinance for determining the fertilizer requirement . It stipulates that soil nitrogen must be determined at least once a year . This can be done either through a laboratory analysis of the Nmin value in spring or through the adoption of test results from comparable areas. Each agricultural enterprise can decide for itself whether it wants to have an exact laboratory analysis carried out on its own fields or whether it wants to use the values from the comparative values that appear in the weekly agricultural papers during the fertilization period in spring. For phosphate, on the other hand, an analysis is mandatory. This must be carried out on all agricultural areas from a size of 1 hectare - with a few exceptions - at least every 6 years. The determination of phosphate is part of the extensive soil analysis. The plant nutrients phosphate , potassium and magnesium as well as the pH value are determined. The aim of the investigations is to enable needs-based fertilization and thus to reduce nutrient inputs into surface water, groundwater and other ecosystems. The entry of nutrients washed away from agricultural areas, especially phosphate, can lead to eutrophication in stagnant and slow-flowing waters and should therefore be avoided. A nitrogen fertilization that goes beyond the needs of the plants leads to nitrate leaching into the groundwater.
By sampling several locations in an agricultural field , this can be divided into so-called partial fields. The resulting different results of the partial fields can be used for the next fertilization in order to supply each of these partial fields with different nutrient contents. This avoids over-fertilization , which saves costs and prevents fertilizer from being leached into the groundwater.
Before a nutrient analysis can be carried out on the soil samples, extensive sample preparation is required. The samples must first be dried and then finely ground with a floor mill. Then a precisely defined amount of the soil sample is weighed out and an extraction solution is added.
Continuous flow analyzer for phosphate and nitrate analyzes
Atomic absorption spectrophotometer for measuring nutrients such as potassium and magnesium
Ciliates colonize the soil in great abundance of species
Further areas of application
- In the context of contaminated site investigations, soil samples are taken to prove the existence of hazardous substances.
- Soil samples are also taken to rule out the spread of soil-borne pathogens, such as potato cancer . A few years after the occurrence of the disease, cultivation tests in the soil taken from the mixed sample are used to determine whether a cultivation ban is still justified for the area in question.
- Determination of chemical soil properties such as soil pH value
literature
- Arnold Finck : Plant nutrition in brief . 3rd revised edition. Hirt, Kiel 1976, ISBN 3-554-80197-6 , ( Hirt's key word books )
- Nicole Dickemann: Taking soil samples , in: Rebe & Wein 11 + 12/2012 , p. 18
Web links
supporting documents
- The investigation of soils , Volume I, VDLUFA-Verlag Darmstadt, 1991