What's the difference between subsoil and understratum?

Subsoil

Definition:

(n.) The bed, or stratum, of earth which lies immediately beneath the surface soil.
(v. t.) To turn up the subsoil of.

Example Sentences:

(1) While undoubtedly a good understanding of soil microbiology in terms of pedology exists, little is presently known about unsaturated subsoils, and aquifers.
(2) The burrows of R. opimus were the main shelters and breeding places of the sandflies, but infection was not transmitted equally in all burrows.It was known that the distribution of sandflies within the burrows was influenced by the humidity in the different parts of the burrow and a survey showed that the highest rate of infection of gerbils occurred in the burrows in those areas with the highest subsoil moisture content.Studies of the prevalence of zoonotic cutaneous leishmaniasis among people in the settlements of the Murghab oasis showed that the years with the highest infection rate were also years with slightly higher rainfall and lower air temperatures in this area.
(3) For the population living on the ground floor of a house with a crystalline subsoil, the gamma radiation and the indoor air 222Rn lead to estimated mean exposures of 1.16 mSv and 9.44 mSv effective dose equivalent per year, respectively.
(4) A mean tap water 222Rn content of 38.3 Bq L-1 and 10.4 Bq L-1 was measured in 31 villages with a crystalline subsoil and 73 villages with a sedimentary subsoil, respectively.
(5) The external gamma radiation and the indoor air Rn (222Rn) concentration were measured in 55 houses of the South East Grisons, the Urseren valley, and the Upper Rhine valley (crystalline subsoils) and in 39 houses of the Molasse basin and the Helvetic nappes (sedimentary subsoils).
(6) The radon-222 emanation from 70 samples of Danish soils, subsoils, and sedimentary rocks has been measured.
(7) The cellar 222Rn gas concentration is about six times higher in houses with a crystalline subsoil (1232 Bq m-3) than in houses with a sedimentary subsoil (201 Bq m-3).
(8) In homes located on a crystalline subsoil, a mean cellar gamma level of 1.40 mGy y-1 was measured, which is twice the mean gamma level of 0.70 mGy y-1 found in homes built on a sedimentary subsoil.
(9) In houses with a sedimentary subsoil, these mean exposures lead to 0.68 mSv y-1 and 3.22 mSv y-1, respectively.
(10) Control sweet clover was harvested from gravelly subsoil and processed and fed to another group of guinea pigs for the same period.
(11) Reliable identification of trace amounts of pesticides (e.g., 28 ppt of atrazine) in subsoil, surface and drinking water is clearly demonstrated by AMD-HPTLC using a polarity gradient based on dichloromethane.
(12) Environmental parameters such as temperature and wind, occupant activities, and house-specific parameters such as subsoil geology, leakiness of the substructure to soil gas, and air exchange rate are the main factors influencing Rn entry into a building and its subsequent indoor behavior.
(13) Samples of fly ash, gravelly subsoil, sweet clover, liver, kidneys, and left-rear gastrocnemius muscle of all guinea pigs were freeze-dried and analyzed for 35 elements by neutron activation analysis.
(14) Houses located on a granite, ortho-gneiss or verrucano subsoil have a cellar 222Rn level that is on the average 4.4 times higher than houses which are built on grey-schist or sediments.
(15) No residues were found below a cracked light clay on a sandy subsoil.
(16) In many parts of the world, the land is also sinking – in Venice’s case, subsoil compaction (a result of industrial exploitation of the surrounding area) lowered the city by 20cm between 1950 and 1970.
(17) These metastable precipitates, both organic and inorganic, are readily remobilized on further acidification, and can release aluminium into streams if the solutions are not neutralized in the subsoil.
(18) Radon-222 degasing from the tap water into the indoor air leads to an additional exposure of about 0.11 mSv y-1 and 0.03 mSv y-1 in homes with a crystalline subsoil and homes with a sedimentary subsoil, respectively.
(19) Since the sixties we have given attention to the problems in the use of pesticides, with regard to organochlorine, we have been investigating either environmental pollution (surface and subsoil water, food, etc.)
(20) When it rains or the land floods, the water trickles through the gravel and sand and slowly charges the subsoil.