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Environmental Analysis Processing of Soil Samples for Nutrient Analysis


Soil is the loose covering of earth’s topmost surface, which is practically always active. Downwards the soil is bordered by solid or loose rocks. Towards the top it is mostly bordered by a cover of vegetation, as well as the atmosphere. Where the topmost layer of soil is covered by water, lakes, rivers and oceans it is considered sediment rather than soil. Depending on perceptions and scientific discipline “soil” can be defined differently.


In geology and in soil science the term soil is categorized according to DIN 4022 as follows:


Gravel - The fraction of the soil with a diameter of > 2 mm is considered as gravel, which again is divided into coarse-, medium- and fine gravel.


Sand - The grain fraction between 0.063 mm and 2.0 mm is identified as sand, which again is differentiated into coarse-, medium- and fine sand.


Coarse clay or silt - Contents of the soil equivalence diameter between 0,002 mm and 0,063 mm are grouped in coarse-, medium- and fine silt. This cohesive soil layer is referred to in general terms also as clay.


Clay - Elements of the soil smaller than 0,002 mm (2µm) are considered as clay. Scientifically it is proven, that all segments of gravel – the contents of the soil


larger than 2 mm - are not available as nutrients for plants and also do not bond nutrients. It is also referred to as coarse soil. All soil contents with an equivalence diameter of 2 mm and smaller however, deliver nutrients for the plants themselves or bind nutrients for the plants, for example in the form of added fertilizer. This type of fraction is considered as fine soil.


For the preparation of agricultural soil samples for the analysis of nutrients, the VDLUFA demands in the book of methods Volume 1 “Analysis of soils” the separation of coarse and fine soil.


For examinations of radioactivity in the environment, the pre-treatment of the sample is described in DIN ISO 18589-2, radioactivity in the environment – soil part 2.


Also for examination of past polluted areas, the Federal Soil Protection and Past Contaminated Area Ordinance, assumes a separation at 2 mm.


This results in the following task: The sieving off and deagglomeration of soil samples of 2 mm.


During the preparation of soil samples, the shares of the coarse soil may not be comminuted, because then they would be considered as part of the fine soil, which would reveal a “dilution” of the contents of the fine soil. The results would be low analysis values of the nutrients and harmful substances - but still, agglomerates from fine contents have to be crushed in order to be driven through a 2 mm sieve.


The conceptional design of the Soil Deagglomerator PULVERISETTE 8 from FRITSCH (Germany) guarantees with almost all soil samples, that for one, the agglomerates, which are almost rock hard, can be opened up and on the other hand that the coarse soil will not be comminuted. The rocks are collected in a separate collection vessel.


It may become problematic with highly binding soils or soils with a large share of rocks. Large rocks should be sorted out. High binding soils while damp should be spread out broadly and then air dried. Should, despite these measures not all agglomerates been crushed, in a few cases the samples have to be prepared or reworked. In the example a wooden hammer was used. In any case, it is to be ensured that no particles larger than 2 mm shall be comminuted and therefore distorting the sample.


Reader Reply Card no 76


Portable Water Activity Meter Helps Scientists Search for Life in Dry Valleys


Scientists from the New Zealand Terrestrial Antarctic Biocomplexity Survey (nzTABS) project are using a Decagon Devices Pawkit portable water activity meter from Labcell (UK) to study soil samples and gain a better understanding of biodiversity in the McMurdo Dry Valleys of Antarctica.


The nzTABS project, which is hosted by the International Centre for


Terrestrial Antarctic Research (ICTAR) at the University of Waikato, New Zealand, is investigating biodiversity in one of the world’s coldest and driest habitats by combining soil water activity data with the results from molecular genetic and geochemical analyses. Doug McCauley and Dr Charles Lee, both of the University of Waikato, have used the Pawkit for three successive field seasons, finding it a very simple and effective way to obtain water activity (aw) measurements immediately after soil samples have been collected. The instrument’s robustness, ease of calibration and simple operation make it a straightforward task to collect reliable aw readings that are accurate to +/-0.02aw.


With extremely low water content and relative humidity, together with low temperatures, the overall conditions in the McMurdo Dry Valleys are barely sufficient to sustain life. However, measuring water content and


relative humidity are not reliable indicators of the sustainability of life, because other factors - such as the electrostatic forces around soil particles (the hygroscopic layer) and chemical bonding (hydration shells) - can trap the water, making it unavailable to organisms. On the other hand, water activity is a measure of the amount of water that is freely available, which is a far superior indicator.


Using the battery-powered, pocket -sized Pawkit is very easy: the user simply has to open the clamshell case, place the sample dish inside and press a button. Readings are obtained in just five minutes from samples of solid, liquid or powdered material, with an accuracy of +/-0.02 aw and a resolution of 0.01 aw over the instrument’s measurement range of 0 to 1.00 aw. A large, clear LCD display shows both the water activity value and the temperature at which the measurement was taken. Despite its small size, the Pawkit is a highly capable instrument thanks to the use of dielectric humidity sensor technology. The robust sensor permits operation in environmental conditions of 5-50o is easy to check the calibration at any time. Battery life is typically three years.


C and 0-90% relative humidity, and it Reader Reply Card no 78


Genevac (UK) reports on the significant operational benefits of using heat transfer plates in conjunction with a centrifugal evaporator for removal of high boiling point solvents such as water from microplate samples.


By specifying an evaporator such as the Genevac HT4X or EZ-2 with high power lamps the overall drying times for aqueous or DMSO sample solutions can be cut to just one fifth of that required without heat transfer plates. Consequently more microplates can be safely dried leading to higher throughput, a key goal for busy laboratories.


Traditionally removing solvents such as DMSO or water from microplates has been time consuming because of the poor thermal contact of the microplate with the evaporator sample holder. However Genevac heat transfer plates overcome this problem acting as a snugly fitting insert beneath the microplate facilitating efficient thermal energy transfer from the hot outer surface of the sample holder directly to the walls of the microplate. This tight fit ensures maximum heat transfer into the samples resulting in very rapid evaporation rates without the risk of overheating fast drying samples. Genevac provides optimised heat transfer plates for most popular brands of microplates.


Reader Reply Card no 77


Checking Climatic Parameters by Hand


Rapid Sample Safe Removal of High Boiling Solvents


The HygroPalm22 from Rotronic (Switzerland) is regarded as the perfect hand-held measuring unit for checking climatic parameters. Its usable ranges are 0...100 %rh / - 10..60 °C, and all psychrometric calculations are possible. The probe can be changed in seconds, and a mini-USB interface allows connection to a PC.


The case contains all the accessories needed for users to calibrate their measuring unit themselves, quickly, simply and independent of location.


The contents comprise: 1 HygroPalm22, 1 calibration device, 1 extension, 1 calibration solution and 1 climatic probe. The set is suitable for a wide range of applications in the foodstuff and pharmaceutical industry, the print and paper sector, trades, research, meteorology, agriculture and climatology.


Reader Reply Card no 79


AET August/September 2010


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