Physical properties of soil#Temperature

{{Main|Soil texture}}

File:SoilTexture USDA.svgs by clay, silt, and sand composition as used by the USDA]] File:Kootenay National Park - Paint Pots 1.jpg, Canada]]

The mineral components of soil are sand, silt and clay, and their relative proportions determine the soil texture. Properties that are influenced by soil texture include porosity, permeability, infiltration, shrink-swell rate, water-holding capacity, and susceptibility to erosion. In the illustrated USDA textural classification triangle, the only soil in which neither sand, silt nor clay predominates is called loam. While even pure sand, silt or clay may be considered a soil, from the perspective of conventional agriculture a loam soil with a small amount of organic material is considered ideal, inasmuch as fertilizers or manure are currently used to mitigate nutrient losses due to crop yields in the long term.{{cite journal |last1=Haynes |first1=Richard J. |last2=Naidu |first2=Ravi |journal=Nutrient cycling in agroecosystems |volume=51 |issue=2 |title=Influence of lime, fertilizer and manure applications on soil organic matter content and soil physical conditions: a review |url=https://www.academia.edu/56259441 |year=1998 |pages=123–37 |doi=10.1023/A:1009738307837 |bibcode=1998NCyAg..51..123H |s2cid=20113235 |access-date=3 June 2025 }} The mineral constituents of a loam soil might be 40% sand, 40% silt and the balance 20% clay by weight. Soil texture affects soil behaviour, in particular, its retention capacity for nutrients (e.g., cation exchange capacity){{cite journal |last1=Silver |first1=Whendee L. |authorlink1=Whendee Silver |last2=Neff |first2=Jason |last3=McGroddy |first3=Megan |last4=Veldkamp |first4=Ed |last5=Keller |first5=Michael |last6=Cosme |first6=Raimundo |journal=Ecosystems |volume=3 |issue=2 |title=Effects of soil texture on belowground carbon and nutrient storage in a lowland Amazonian forest ecosystem |url=https://www.researchgate.net/publication/225102185 |year=2000 |pages=193–209 |doi=10.1007/s100210000019 |bibcode=2000Ecosy...3..193S |s2cid=23835982 |access-date=3 June 2025 }} and water.

Sand and silt are the products of physical and chemical weathering of the parent rock;{{cite book |last=Jenny |first=Hans |title=Factors of soil formation: a system of qunatitative pedology |year=1941 |publisher=McGraw-Hill |location=New York |url=https://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20170808104008/http://netedu.xauat.edu.cn/sykc/hjx/content/ckzl/6/2.pdf |archive-date=8 August 2017 |url-status=live }} clay, on the other hand, is most often the product of the precipitation of the dissolved parent rock as a secondary mineral, except when derived from the weathering of mica.{{cite journal |last=Jackson |first=Marion L. |journal=Clays and Clay Minerals |volume=6 |issue=1 |title=Frequency distribution of clay minerals in major great soil groups as related to the factors of soil formation |year=1957 |pages=133–43 |doi=10.1346/CCMN.1957.0060111 |bibcode=1957CCM.....6..133J |url=https://fr.1lib.sk/book/107829728/a4837c |access-date=3 June 2025 }} It is the surface area to volume ratio (specific surface area) of soil particles and the unbalanced ionic electric charges within those that determine their role in the fertility of soil, as measured by its cation exchange capacity.{{cite journal |last1=Petersen |first1=Lis Wollesen |last2=Moldrup |first2=Per |last3=Jacobsen |first3=Ole Hørbye |last4=Rolston |first4=Dennis E. |journal=Soil Science |volume=161 |issue=1 |title=Relations between specific surface area and soil physical and chemical properties |url=https://www.academia.edu/22117440 |year=1996 |pages=9–21 |doi=10.1097/00010694-199601000-00003 |access-date=3 June 2025 |bibcode=1996SoilS.161....9P }}{{cite book |last=Lewis |first=D. R. |date=1955 |chapter=Ion exchange reactions of clays |title=Clays and clay technology |editor1-last=Pask |editor1-first=Joseph A. |editor2-last=Turner |editor2-first=Mort D. |publisher=State of California, Department of Natural Resources, Division of Mines |location=San Francisco, California |pages=54–69 |chapter-url=https://fr.1lib.sk/book/89626113/088d2e |access-date=11 June 2025 }} Sand is least active, having the least specific surface area, followed by silt; clay is the most active. Sand's greatest benefit to soil is that it resists compaction and increases soil porosity, although this property stands only for pure sand, not for sand mixed with smaller minerals which fill the voids among sand grains.{{cite journal |last=Dexter |first=Anthony R. |journal=Geoderma |volume=120 |issue=3–4 |title=Soil physical quality. I. Theory, effects of soil texture, density, and organic matter, and effects on root growth |year=2004 |pages=201–14 |doi=10.1016/j.geoderma.2003.09.004 |url=https://fr.1lib.sk/book/49014606/f33028 |access-date=3 June 2025 }} Silt is mineralogically like sand but with its higher specific surface area it is more chemically and physically active than sand. But it is the clay content of soil, with its very high specific surface area and generally large number of negative charges, that gives a soil its high retention capacity for water and nutrients. Clay soils also resist wind and water erosion better than silty and sandy soils, as the particles bond tightly to each other,{{cite journal |last=Bouyoucos |first=George J. |journal=Journal of the American Society of Agronomy |volume=27 |issue=9 |title=The clay ratio as a criterion of susceptibility of soils to erosion |year=1935 |pages=738–41 |doi=10.2134/agronj1935.00021962002700090007x |bibcode=1935AgrJ...27..738B |url=https://fr.1lib.sk/book/108864459/950e6c |access-date=3 June 2025 }} and that with a strong mitigation effect of organic matter.{{cite journal |last1=Borrelli |first1=Pasquale |last2=Ballabio |first2=Cristiano |last3=Panagos |first3=Panos |last4=Montanarella |first4=Luca |journal=Geoderma |volume=232–234 |title=Wind erosion susceptibility of European soils |url=https://www.researchgate.net/publication/263092389 |year=2014 |pages=471–78 |doi=10.1016/j.geoderma.2014.06.008 |access-date=3 June 2025 |bibcode=2014Geode.232..471B }}

Sand is the most stable of the mineral components of soil; it consists of rock fragments, primarily quartz particles, ranging in size from {{convert|2.0|to|0.05|mm|in|abbr=on}} in diameter. Silt ranges in size from {{convert|0.05|to|0.002|mm|in|abbr=on}}. Clay cannot be resolved by optical microscopes as its particles are {{convert|0.002|mm|in|abbr=on}} or less in diameter and a thickness of only 10 angstroms (10⁻¹⁰ m).{{sfn|Russell|1957|pp=32–33}}{{sfn|Flemming|1957|p=331}} In medium-textured soils, clay is often washed downward through the soil profile (a process called eluviation) and accumulates in the subsoil (a process called illuviation). There is no clear relationship between the size of soil mineral components and their mineralogical nature: sand and silt particles can be calcareous as well as siliceous,{{cite journal |last1=Wei |first1=Xiaobing |last2=Lu |first2=Yani |last3=Liu |first3=Xiaoxuan |last4=Zhang |first4=Biwen |last5=Luo |first5=Mingxing |last6=Zhong |first6=Li |journal=Scientific Reports |volume=14 |issue=18465 |title=Particle shape analysis of calcareous sand based on digital images |url=https://www.researchgate.net/publication/382998712 |year=2024 |pages=1–15 |doi=10.1038/s41598-024-69197-7 |access-date=3 June 2025 }} while textural clay ({{convert|0.002|mm|in|abbr=on}}) can be made of very fine quartz particles as well as of multi-layered secondary minerals.{{cite book |last=Grim |first=Ralph E. |date=1953 |title=Clay mineralogy |publisher=McGraw-Hill |location=New York, New York |url=http://krishikosh.egranth.ac.in/bitstream/1/2037422/1/1334.pdf |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20171224213926/http://krishikosh.egranth.ac.in/bitstream/1/2037422/1/1334.pdf |archive-date=24 December 2017 |url-status=live }} Soil mineral components belonging to a given textural class may thus share properties linked to their specific surface area (e.g. moisture retention) but not those linked to their chemical composition (e.g. cation exchange capacity).

Soil components larger than {{convert|2.0|mm|in|abbr=on}} are classed as rock and gravel and are removed before determining the percentages of the remaining components and the textural class of the soil, but are included in the name. For example, a sandy loam soil with 20% gravel would be called gravelly sandy loam.

When the organic component of a soil is substantial, the soil is called organic soil rather than mineral soil. A soil is called organic if:

1. Mineral fraction is 0% clay and organic matter is 20% or more
2. Mineral fraction is 0% to 50% clay and organic matter is between 20% and 30%
3. Mineral fraction is 50% or more clay and organic matter 30% or more.{{sfn|Donahue|Miller|Shickluna|1977|p=53}}

{{Main|Ped|Soil structure|Structural Soil}}

The clumping of the soil textural components of sand, silt and clay causes aggregates to form and the further association of those aggregates into larger units creates soil structures called peds (a contraction of the word pedolith). The adhesion of the soil textural components by organic substances, iron oxides, carbonates, clays, and silica, the breakage of those aggregates from expansion-contraction caused by freezing-thawing and wetting-drying cycles,{{cite journal |last1=Sillanpää |first1=Mikko |last2=Webber |first2=L. R. |journal=Canadian Journal of Soil Science |volume=41 |issue=2 |title=The effect of freezing-thawing and wetting-drying cycles on soil aggregation |year=1961 |pages=182–87 |doi=10.4141/cjss61-024 |doi-access=free }} and the build-up of aggregates by soil animals, microbial colonies and root tips{{cite journal |last=Oades |first=J. Malcolm |journal=Geoderma |volume=56 |issue=1–4 |title=The role of biology in the formation, stabilization and degradation of soil structure |url=https://www.dendrocronologia.cl/pubs/Oades%201992.pdf |year=1993 |pages=377–400 |doi=10.1016/0016-7061(93)90123-3 |access-date=3 June 2025 |bibcode=1993Geode..56..377O }} shape soil into distinct geometric forms.{{cite journal |last1=Bronick |first1=Carol J. |last2=Lal |first2=Ratan |title=Soil structure and management: a review |journal=Geoderma |date=January 2005 |volume=124 |issue=1–2 |pages=3–22 |doi=10.1016/j.geoderma.2004.03.005 |url=http://tinread.usarb.md:8888/tinread/fulltext/lal/soil_structure.pdf |access-date=3 June 2025 |bibcode=2005Geode.124....3B }}{{cite journal |last1=Lee |first1=Kenneth Ernest |last2=Foster |first2=Ralph C. |year=2003 |title=Soil fauna and soil structure |journal=Australian Journal of Soil Research |volume=29 |issue=6 |pages=745–75 |doi=10.1071/SR9910745 |url=https://www.academia.edu/102507924 |access-date=3 June 2025 }} The peds evolve into units which have various shapes, sizes and degrees of development.{{cite web |author=Soil Science Division Staff |year=2017 |url=https://www.nrcs.usda.gov/sites/default/files/2022-09/The-Soil-Survey-Manual.pdf |title=Soil structure |website=Soil Survey Manual (issued March 2017), USDA Handbook No. 18 |publisher=United States Department of Agriculture, Natural Researches Conservation Service, Soils |location=Washington, DC |pages=155–63 |access-date=3 June 2025 |archive-date=7 November 2017 |archive-url=https://web.archive.org/web/20171107023728/https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054253#soil_structure |url-status=live }} A soil clod, however, is not a ped but rather a mass of soil that results from mechanical disturbance of the soil such as cultivation. Soil structure affects aeration, water movement, conduction of heat, plant root growth and resistance to erosion.{{cite journal |last1=Horn |first1=Rainer |last2=Taubner |first2=Heidi |last3=Wuttke |first3=M. |last4=Baumgartl |first4=Thomas |journal=Soil and Tillage Research |volume=30 |issue=2–4 |title=Soil physical properties related to soil structure |year=1994 |pages=187–216 |doi=10.1016/0167-1987(94)90005-1 |bibcode=1994STilR..30..187H |url=https://fr.1lib.sk/book/34162332/e82efc |access-date=3 June 2025 }} Water, in turn, has a strong effect on soil structure, directly via the dissolution and precipitation of minerals, the mechanical destruction of aggregates (slaking){{cite web |last1=Murray |first1=Robert S. |last2=Grant |first2=Cameron D. |year=2007 |title=The impact of irrigation on soil structure |url=https://library.dbca.wa.gov.au/static/FullTextFiles/070521.pdf |access-date=3 June 2025 }} and indirectly by promoting plant, animal and microbial growth.

Soil structure often gives clues to its texture, organic matter content, biological activity, past soil evolution, human use, and the chemical and mineralogical conditions under which the soil formed. While texture is defined by the mineral component of a soil and is an innate property of the soil that does not change with agricultural activities, soil structure can be improved or destroyed by the choice and timing of farming practices.

Soil structural classes:{{sfn|Donahue|Miller|Shickluna|1977|pp=55–56}}

1. Types: Shape and arrangement of peds
2. Platy: Peds are flattened one atop the other 1–10 mm thick. Found in the A-horizon of forest soils and lake sedimentation.
3. Prismatic and Columnar: Prismlike peds are long in the vertical dimension, 10–100 mm wide. Prismatic peds have flat tops, columnar peds have rounded tops. Tend to form in the B-horizon in high sodium soil where clay has accumulated.
4. Angular and subangular: Blocky peds are imperfect cubes, 5–50 mm, angular have sharp edges, subangular have rounded edges. Tend to form in the B-horizon where clay has accumulated and indicate poor water penetration.
5. Granular and Crumb: Spheroid peds of polyhedrons, 1–10 mm, often found in the A-horizon in the presence of organic material. Crumb peds are more porous and are considered ideal.
6. Classes: Size of peds whose ranges depend upon the above type
7. Very fine or very thin: <1 mm platy and spherical; <5 mm blocky; <10 mm prismlike.
8. Fine or thin: 1–2 mm platy, and spherical; 5–10 mm blocky; 10–20 mm prismlike.
9. Medium: 2–5 mm platy, granular; 10–20 mm blocky; 20–50 prismlike.
10. Coarse or thick: 5–10 mm platy, granular; 20–50 mm blocky; 50–100 mm prismlike.
11. Very coarse or very thick: >10 mm platy, granular; >50 mm blocky; >100 mm prismlike.
12. Grades: Is a measure of the degree of development or cementation within the peds that results in their strength and stability.
13. Weak: Weak cementation allows peds to fall apart into the three textural constituents, sand, silt and clay.
14. Moderate: Peds are not distinct in undisturbed soil but when removed they break into aggregates, some broken aggregates and little unaggregated material. This is considered ideal.
15. Strong:Peds are distinct before removed from the profile and do not break apart easily.
16. Structureless: Soil is entirely cemented together in one great mass such as slabs of clay or no cementation at all such as with sand.

At the largest scale, the forces that shape a soil's structure result from swelling and shrinkage that initially tend to act horizontally, causing vertically oriented prismatic peds. This mechanical process is mainly exemplified in the development of vertisols.{{cite journal |last1=Dinka |first1=Takele M. |last2=Morgan |first2=Cristine L.S. |last3=McInnes |first3=Kevin J. |last4=Kishné |first4= Andrea Sz. |last5=Harmel |first5=R. Daren |journal=Journal of Hydrology |volume=476 |title=Shrink–swell behavior of soil across a Vertisol catena |url=https://www.academia.edu/13776567 |year=2013 |pages=352–59 |doi=10.1016/j.jhydrol.2012.11.002 |access-date=3 June 2025 |bibcode=2013JHyd..476..352D }} Clayey soil, due to its differential drying rate with respect to the surface, will induce horizontal cracks, reducing columns to blocky peds.{{cite journal |last1=Morris |first1=Peter H. |last2=Graham |first2=James |last3=Williams |first3=David J. |journal=Canadian Geotechnical Journal |volume=29 |issue=2 |title=Cracking in drying soils |url=https://www.researchgate.net/publication/239487071 |year=1992 |pages=263–77 |doi=10.1139/t92-030 |access-date=3 June 2025 }} Roots, rodents, worms, and freezing-thawing cycles further break the peds into smaller peds of a more or less spherical shape.

At a smaller scale, plant roots extend into voids (macropores) and remove water{{cite journal |last1=Robinson |first1=Nicole |last2=Harper |first2=R.J. |last3=Smettem |first3=Keith Richard J. |journal=Plant and Soil |volume=286 |issue=1–2 |title=Soil water depletion by Eucalyptus spp. integrated into dryland agricultural systems |url=https://www.researchgate.net/publication/43501164 |year=2006 |pages=141–51 |doi=10.1007/s11104-006-9032-4 |bibcode=2006PlSoi.286..141R |s2cid=44241416 |access-date=3 June 2025 }} causing macroporosity to increase and microporosity to decrease,{{cite journal |last1=Scholl |first1=Peter |last2=Leitner |first2=Daniel |last3=Kammerer |first3=Gerhard |last4=Loiskandl |first4=Willibald |last5=Kaul |first5=Hans-Peter |last6=Bodner |first6=Gernot |journal=Plant and Soil |volume=381 |issue=1–2 |title=Root induced changes of effective 1D hydraulic properties in a soil column |year=2014 |pages=193–213 |doi=10.1007/s11104-014-2121-x |pmid=25834290 |pmc=4372835 |bibcode=2014PlSoi.381..193S |url=https://www.researchgate.net/publication/271702247 |access-date=3 June 2025 }} thereby decreasing aggregate size.{{cite journal |last1=Angers |first1=Denis A. |last2=Caron |first2=Jean |journal=Biogeochemistry |volume=42 |issue=1 |title=Plant-induced changes in soil structure: processes and feedbacks |url=https://www.researchgate.net/publication/226938344 |year=1998 |pages=55–72 |doi=10.1023/A:1005944025343 |bibcode=1998Biogc..42...55A |s2cid=94249645 |access-date=3 June 2025 }} At the same time, root hairs and fungal hyphae create microscopic tunnels (micropores) that break up peds.{{cite journal |last1=White |first1=Rosemary G. |last2=Kirkegaard |first2=John A. |journal=Plant, Cell and Environment |volume=33 |issue=2 |title=The distribution and abundance of wheat roots in a dense, structured subsoil: implications for water uptake |url=https://www.academia.edu/402626 |year=2010 |pages=133–48 |doi=10.1111/j.1365-3040.2009.02059.x |pmid=19895403 |access-date=3 June 2025 }}{{cite journal |last1=Skinner |first1=Malcolm F. |last2=Bowen |first2=Glynn D. |journal=Soil Biology and Biochemistry |volume=6 |issue=1 |title=The penetration of soil by mycelial strands of ectomycorrhizal fungi |year=1974 |pages=57–8 |doi=10.1016/0038-0717(74)90012-1 |bibcode=1974SBiBi...6IN359S |url=https://fr.1lib.sk/book/51954579/199472 |access-date=3 June 2025 }}

At an even smaller scale, soil aggregation continues as bacteria and fungi exude sticky polysaccharides which bind soil into smaller peds.{{cite journal |last=Chenu |first=Claire |journal=Geoderma |volume=56 |issue=1–4 |title=Clay- or sand-polysaccharide associations as models for the interface between micro-organisms and soil: water related properties and microstructure |url=https://www.academia.edu/12012172 |year=1993 |pages=143–56 |doi=10.1016/0016-7061(93)90106-U |access-date=3 June 2025 |bibcode=1993Geode..56..143C }} The addition of the raw organic matter that bacteria and fungi feed upon encourages the formation of this desirable soil structure.{{cite journal |last=Franzluebbers |first=Alan J. |journal=Soil and Tillage Research |volume=66 |issue=2 |title=Water infiltration and soil structure related to organic matter and its stratification with depth |url=https://fr.1lib.sk/book/40810160/d765df |year=2002 |pages=197–205 |doi=10.1016/S0167-1987(02)00027-2 |bibcode=2002STilR..66..197F |access-date=3 June 2025 }}

At the lowest scale, the soil chemistry affects the aggregation or dispersal of soil particles. The clay particles contain polyvalent cations, such as aluminium, which give the faces of clay layers localized negative electric charges.{{cite journal |last1=Sposito |first1=Garrison |last2=Skipper |first2=Neal T. |last3=Sutton |first3=Rebecca |last4=Park |first4=Sung-Ho |last5=Soper |first5=Alan K. |last6=Greathouse |first6=Jeffery A. |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=96 |issue=7 |title=Surface geochemistry of the clay minerals |year=1999 |pages=3358–64 |doi=10.1073/pnas.96.7.3358 |pmid=10097044 |bibcode=1999PNAS...96.3358S |pmc=34275 |doi-access=free }} At the same time, the edges of the clay plates have a slight positive charge, due to the sorption of aluminium from the soil solution to exposed hydroxyl groups, thereby allowing the edges to adhere to the negative charges on the faces of other clay particles or to flocculate (form clumps).{{cite journal |last1=Tombácz |first1=Etelka |last2=Szekeres |first2=Márta |journal=Applied Clay Science |volume=34 |issue=1–4 |title=Surface charge heterogeneity of kaolinite in aqueous suspension in comparison with montmorillonite |url=https://www.academia.edu/886679 |year=2006 |pages=105–24 |doi=10.1016/j.clay.2006.05.009 |bibcode=2006ApCS...34..105T |access-date=3 June 2025 }} On the other hand, when monovalent ions, such as sodium, invade and displace the polyvalent cations (single displacement reaction), they weaken the positive charges on the edges, while the negative surface charges are relatively strengthened. This leaves negative charge on the clay faces that repel other clay, causing the particles to push apart, and by doing so deflocculate clay suspensions.{{cite journal |last1=Pĕnkavová |first1=Věra |last2=Guerreiro |first2=Margarida |last3=Tihon |first3=Jaroslav |last4=Teixeira |first4=José A. C. |journal=Applied Rheology |volume=25 |issue=2 |title=Deflocculation of kaolin suspensions: the effect of various electrolytes |year=2019 |page=24151 |doi=10.3933/APPLRHEOL-25-24151 |doi-access=free }} As a result, the clay disperses and settles into voids between peds, causing those to close. In this way the open structure of the soil is destroyed and the soil is made impenetrable to air and water.{{cite journal |last1=Shainberg |first1=Isaac |last2=Letey |first2=John |journal=Hilgardia |volume=52 |issue=2 |title=Response of soils to sodic and saline conditions |url=https://www.researchgate.net/publication/280260130 |year=1984 |pages=1–57 |doi=10.3733/hilg.v52n02p057 |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20171211053318/http://hilgardia.ucanr.edu/fileaccess.cfm?article=152852&p=VAFSNP |archive-date=11 December 2017 |url-status=live }} Such sodic soil (also called haline soil) tends to form columnar peds near the surface.{{cite journal |last1=Young |first1=Michael H. |last2=McDonald |first2=Eric V. |last3=Caldwell |first3=Todd G. |last4=Benner |first4=Shawn G. |last5=Meadows |first5=Darren G. |journal=Vadose Zone Journal |volume=3 |issue=3 |title=Hydraulic properties of a desert soil chronosequence in the Mojave Desert, USA |url=https://www.researchgate.net/publication/237274001 |archive-url=https://web.archive.org/web/20180616153949/https://pdfs.semanticscholar.org/c937/e83cd6c3bb8a685de6ae1adf5ba7602907a5.pdf |url-status=live |archive-date=16 June 2018 |year=2004 |pages=956–63 |doi=10.2113/3.3.956 |bibcode=2004VZJ.....3..956Y |s2cid=51769309 |access-date=3 June 2025 }}

{{see also|Bulk density#Soil}}

Soil particle density is typically 2.60 to 2.75 grams per cm³ and is usually unchanging for a given soil.{{cite web |url=https://resrad.evs.anl.gov/docs/data_collection.pdf |last1=Yu |first1=Charley |last2=Kamboj |first2=Sunita |last3=Wang |first3=Cheng |last4=Cheng |first4=Jing-Jy |title=Data collection handbook to support modeling impacts of radioactive material in soil and building structures |pages=13–21 |website=Argonne National Laboratory |year=2015 |archive-url=https://web.archive.org/web/20180804105951/http://resrad.evs.anl.gov/docs/data_collection.pdf |archive-date=2018-08-04 |url-status=live |access-date=3 June 2025 }} Soil particle density is lower for soils with high organic matter content,{{cite journal |last1=Blanco-Canqui |first1=Humberto |last2=Lal |first2=Rattan |last3=Post |first3=Wilfred M. |last4=Izaurralde |first4=Roberto Cesar |last5=Shipitalo |first5=Martin J. |journal=Soil Science Society of America Journal |volume=70 |issue=4 |title=Organic carbon influences on soil particle density and rheological properties |url=https://www.academia.edu/65840415 |year=2006 |pages=1407–14 |doi=10.2136/sssaj2005.0355 |access-date=3 June 2025 |bibcode=2006SSASJ..70.1407B }} and is higher for soils with high iron-oxides content.{{cite book |last1=Cornell |first1=Rochelle M. |last2=Schwertmann |first2=Udo |date=2003 |title=The iron oxides: structure, properties, reactions, occurrences and uses |edition=2nd |location=Weinheim, Germany |publisher=Wiley-VCH |url=https://fr.1lib.sk/book/2153488/e2c4e8 |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20171226020624/http://epsc511.wustl.edu/IronOxide_reading.pdf |archive-date=26 December 2017 |url-status=live }} Soil bulk density is equal to the dry mass of the soil divided by the volume of the soil; i.e., it includes air space and organic materials of the soil volume. Thereby soil bulk density is always less than soil particle density and is a good indicator of soil compaction.{{cite journal |last1=Håkansson |first1=Inge |last2=Lipiec |first2=Jerzy |journal=Soil and Tillage Research |volume=53 |issue=2 |title=A review of the usefulness of relative bulk density values in studies of soil structure and compaction |url=https://www.researchgate.net/publication/222541793 |archive-url=https://web.archive.org/web/20171022193657/https://pdfs.semanticscholar.org/b028/6fcacb6e12473bd1d4796a9a053eb20d5d72.pdf |url-status=live |archive-date=22 October 2017 |year=2000 |pages=71–85 |doi=10.1016/S0167-1987(99)00095-1 |bibcode=2000STilR..53...71H |s2cid=30045538 |access-date=3 June 2025 }} The soil bulk density of cultivated loam is about 1.1 to 1.4 g/cm³ (for comparison water is 1.0 g/cm³).{{sfn|Donahue|Miller|Shickluna|1977|pp=59–61}} Contrary to particle density, soil bulk density is highly variable for a given soil, with a strong causal relationship with soil biological activity and management strategies.{{cite journal |last1=Mäder |first1=Paul |last2=Fließbach |first2=Andreas |last3=Dubois |first3=David |last4=Gunst |first4=Lucie |last5=Fried |first5=Padruot |last6=Liggli |first6=Urs |journal=Science |volume=296 |issue=1694 |title=Soil fertility and biodiversity in organic farming |url=https://www.researchgate.net/publication/11333301 |year=2002 |pages=1694–97 |doi=10.1126/science.1071148 |pmid=12040197 |access-date=3 June 2025 |bibcode=2002Sci...296.1694M |s2cid=7635563 }} However, it has been shown that, depending on species and the size of their aggregates (faeces), earthworms may either increase or decrease soil bulk density.{{cite book |last1=Blanchart |first1=Éric |last2=Albrecht |first2=Alain |last3=Alegre |first3=Julio |last4=Duboisset |first4=Arnaud |last5=Gilot |first5=Cécile |last6=Pashanasi |first6=Beto |last7=Lavelle |first7=Patrick |last8=Brussaard |first8=Lijbert |date=1999 |chapter=Effects of earthworms on soil structure and physical properties |title=Earthworm management in tropical agroecosystems |edition=1st |editor1-first=Patrick |editor1-last=Lavelle |editor2-first=Lijbert |editor2-last=Brussaard |editor3-first=Paul F. |editor3-last=Hendrix |publisher=CAB International |location=Wallingford, United Kingdom |pages=149–72 |isbn=978-0-85199-270-9 |chapter-url=https://horizon.documentation.ird.fr/exl-doc/pleins_textes/divers16-03/010021558.pdf |access-date=3 June 2025 }} A lower bulk density by itself does not indicate suitability for plant growth due to the confounding influence of soil texture and structure.{{cite journal |last1=Rampazzo |first1=Nicola |last2=Blum |first2=Winfried E.H. |last3=Wimmer |first3=Bernhard |journal=Die Bodenkultur |volume=49 |issue=2 |title=Assessment of soil structure parameters and functions in agricultural soils |url=https://diebodenkultur.boku.ac.at/volltexte/band-49/heft-2/rampazzo.pdf |year=1998 |pages=69–84 |access-date=3 June 2025 }} A high bulk density is indicative of either soil compaction or a mixture of soil textural classes in which small particles fill the voids among coarser particles.{{cite journal |last1=Bodman |first1=Geoffrey Baldwin |last2=Constantin |first2=Winfried G.K. |journal=Hilgardia |volume=36 |issue=15 |title=Influence of particle size distribution in soil compaction |doi=10.3733/hilg.v36n15p567 |url=https://ucanr.edu/sites/UCCE_LR/files/203094.pdf |year=1965 |pages=567–91 |access-date=3 June 2025 }} Hence the positive correlation between the fractal dimension of soil, considered as a porous medium, and its bulk density,{{cite journal |last1=Zeng |first1=Y. |last2=Gantzer |first2=Clark |last3=Payton |first3=R.L. |last4=Anderson |first4=Stephen H. |journal=Soil Science Society of America Journal |volume=60 |issue=6 |title=Fractal dimension and lacunarity of bulk density determined with X-ray computed tomography |doi=10.2136/sssaj1996.03615995006000060016x |url=https://www.researchgate.net/publication/200750939 |year=1996 |pages=1718–24 |access-date=3 June 2025 |bibcode=1996SSASJ..60.1718Z }} that explains the poor hydraulic conductivity of silty clay loam in the absence of a faunal structure.{{cite journal |last1=Rawls |first1=Walter J. |last2=Brakensiek |first2=Donald L. |last3=Saxton |first3=Keith E. |journal=Transactions of the American Society of Agricultural Engineers |volume=25 |issue=5 |title=Estimation of soil water properties |doi=10.13031/2013.33720 |url=https://fr.1lib.sk/book/101138954/31140f |year=1982 |pages=1316–20 |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20170517020519/http://www.envsci.rutgers.edu/~gimenez/SoilPhysics/HomeworkCommonFiles/Rawls%20et%20al%201982.pdf |archive-date=17 May 2017 |url-status=live }}

{{main|Pore space in soil}}

Pore space is that part of the bulk volume of soil that is not occupied by either mineral or organic matter but is open space occupied by either gases or water. In a productive, medium-textured soil the total pore space is typically about 50% of the soil volume.{{cite web |title=Physical aspects of crop productivity |url=https://www.fao.org/3/v9926e/v9926e04.htm |website=www.fao.org |publisher=Food and Agriculture Organization of the United Nations |location=Rome, Italy |access-date=3 June 2025 }} Pore size varies considerably; the smallest pores (cryptopores; <0.1 μm) hold water too tightly for use by plant roots; plant-available water is held in ultramicropores, micropores and mesopores (0.1–75 μm); and macropores (>75 μm) are generally air-filled when the soil is at field capacity.

Soil texture determines total volume of the smallest pores;{{cite journal |last1=Rutherford |first1=P. Michael |last2=Juma |first2=Noorallah G. |journal=Biology and Fertility of Soils |volume=12 |issue=4 |title=Influence of texture on habitable pore space and bacterial-protozoan populations in soil |year=1992 |pages=221–27 |doi=10.1007/BF00336036 |bibcode=1992BioFS..12..221R |s2cid=21083298 |url=https://fr.1lib.sk/book/37619665/ea10e6 |access-date=3 June 2025 }} clay soils have smaller pores, but more total pore space than sands,{{cite journal |last=Diamond |first=Sidney |journal=Clays and Clay Minerals |volume=18 |issue=1 |title=Pore size distributions in clays |url=https://www.researchgate.net/publication/255602213 |year=1970 |pages=7–23 |doi=10.1346/CCMN.1970.0180103 |access-date=3 June 2025 |bibcode=1970CCM....18....7D |s2cid=59017708 }} despite a much lower permeability.{{cite web |title=Permeability of different soils |url=https://archive.nptel.ac.in/content/storage2/courses/105103097/web/chap6final/s3.htm |website=nptel.ac.in |publisher=NPTEL, Government of India |location=Chennai, India |access-date=3 June 2025 |archive-url=https://web.archive.org/web/20180102012804/https://nptel.ac.in/courses/105103097/27 |archive-date=2 January 2018 |url-status=live }} Soil structure has a strong influence on the larger pores that affect soil aeration, water infiltration and drainage.{{sfn|Donahue|Miller|Shickluna|1977|pp=62–63}} Tillage has the short-term benefit of temporarily increasing the number of pores of largest size, but these can be rapidly degraded by the destruction of soil aggregation.{{cite web |url=https://passel2.unl.edu/view/lesson/0cff7943f577 |title=Physical properties of soil and soil water |website=passel.unl.edu |publisher=Plant and Soil Sciences eLibrary |location=Lincoln, Nebraska |access-date=3 June 2025 }}

The pore size distribution affects the ability of plants and other organisms to access water and oxygen; large, continuous pores allow rapid transmission of air, water and dissolved nutrients through soil, and small pores store water between rainfall or irrigation events.{{cite book |last=Nimmo |first=John R. |date=2004 |chapter=Porosity and pore size distribution |title=Encyclopedia of soils in the environment, volume 3 |edition=1st |editor1-first=Daniel |editor1-last=Hillel |editor2-first=Cynthia |editor2-last=Rosenzweig |editor3-first=David |editor3-last=Powlson |editor4-first=Kate |editor4-last=Scow|editor4-link=Kate Scow |editor5-first=Michail |editor5-last=Singer |editor6-first=Donald |editor6-last=Sparks |publisher=Academic Press |location=London, United Kingdom |pages=295–303 |isbn=978-0-12-348530-4 |chapter-url=https://wwwrcamnl.wr.usgs.gov/uzf/abs_pubs/papers/nimmo.04.encyc.por.ese.pdf |access-date=3 June 2025 }} Pore size variation also compartmentalizes the soil pore space such that many microbial and faunal organisms are not in direct competition with one another, which may explain not only the large number of species present, but the fact that functionally redundant organisms (organisms with the same ecological niche) can co-exist within the same soil.{{cite journal |last=Giller |first=Paul S. |journal=Biodiversity and Conservation |volume=5 |issue=2 |title=The diversity of soil communities, the 'poor man's tropical rainforest' |url=https://www.researchgate.net/publication/226978038 |year=1996 |pages=135–68 |doi=10.1007/BF00055827 |bibcode=1996BiCon...5..135G |s2cid=206767237 |access-date=3 June 2025 }}

Consistency is the ability of soil to stick to itself or to other objects (cohesion and adhesion, respectively) and its ability to resist deformation and rupture. It is of approximate use in predicting cultivation problems{{cite journal |last1=Boekel |first1=P. |last2=Peerlkamp |first2=Petrus K. |journal=Netherlands Journal of Agricultural Science |volume=4 |issue=1 |title=Soil consistency as a factor determining the soil structure of clay soils |url=https://library.wur.nl/ojs/index.php/njas/article/view/17792/17206 |year=1956 |pages=122–25 |doi=10.18174/njas.v4i1.17792 |s2cid=91853219 |access-date=3 June 2025 }} and the engineering of foundations.{{cite book |last=Day |first=Robert W. |date=2000 |chapter=Soil mechanics and foundations |title=Building design and construction handbook |edition=6th |editor1-first=Frederick S. |editor1-last=Merritt |editor2-first=Jonathan T. |editor2-last=Rickett |publisher=McGraw-Hill Professional |location=New York |isbn=978-0-07-041999-5 |chapter-url=http://freeit.free.fr/Building%20Design&Construction%20Handbook,6ed/1999X_06.pdf |access-date=3 June 2025 }} Consistency is measured at three moisture conditions: air-dry, moist, and wet.{{cite web |url=https://www.fao.org/fishery/docs/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e08.htm |title=Soil consistency |publisher=Food and Agriculture Organization of the United Nations |location=Rome, Italy |access-date=3 June 2025 }} In those conditions the consistency quality depends upon the clay content. In the wet state, the two qualities of stickiness and plasticity are assessed. A soil's resistance to fragmentation and crumbling is assessed in the dry state by rubbing the sample. Its resistance to shearing forces is assessed in the moist state by thumb and finger pressure. Additionally, the cemented consistency depends on cementation by substances other than clay, such as calcium carbonate, silica, oxides and salts; moisture content has little effect on its assessment. The measures of consistency border on subjective compared to other measures such as pH, since they employ the apparent feel of the soil in those states.

The terms used to describe the soil consistency in three moisture states and a last not affected by the amount of moisture are as follows:

1. Consistency of Dry Soil: loose, soft, slightly hard, hard, very hard, extremely hard
2. Consistency of Moist Soil: loose, very friable, friable, firm, very firm, extremely firm
3. Consistency of Wet Soil: nonsticky, slightly sticky, sticky, very sticky; nonplastic, slightly plastic, plastic, very plastic
4. Consistency of Cemented Soil: weakly cemented, strongly cemented, indurated (requires hammer blows to break up){{sfn|Donahue|Miller|Shickluna|1977|pp=62–63, 565–67}}

Soil consistency is useful in estimating the ability of soil to support buildings and roads. More precise measures of soil strength are often made prior to construction.{{cite journal |last1=Sharma |first1=Sparsh |last2=Ahmed |first2=Suhaib |last3=Naseem |first3=Mohd |last4=Alnumay |first4=Waleed S. |last5=Singh |first5=Saurabh |last6=Cho |first6=Gi Hwan |journal=Sensors |title=A survey on applications of artificial intelligence for pre-parametric project cost and soil shear-strength estimation in construction and geotechnical engineering |year=2021 |volume=21 |page=463 |doi=10.3390/s21020463 |pmid=33440731 |pmc=7827696 |bibcode=2021Senso..21..463S |doi-access=free }}

{{Further|Soil thermal properties|Heat capacity|Thermal conduction}}

Soil temperature depends on the ratio of the energy absorbed to that lost.{{cite journal |last=Deardorff |first=James W. |journal=Journal of Geophysical Research |volume=83 |issue=C4 |title=Efficient prediction of ground surface temperature and moisture, with inclusion of a layer of vegetation |url=https://patarnott.com/atms411/pdf/Deardorff1978GroundTemperature.pdf |year=1978 |pages=1889–903 |doi=10.1029/JC083iC04p01889 |access-date=4 June 2025 |bibcode=1978JGR....83.1889D |citeseerx=10.1.1.466.5266 }} Soil has a mean annual temperature from -10 to 26 °C according to biomes.{{cite journal |last1=Hursh |first1=Andrew |last2=Ballantyne |first2=Ashley |last3=Cooper |first3=Leila |last4=Maneta |first4=Marco |last5=Kimball |first5=John |last6=Watts |first6=Jennifer |journal=Global Change Biology |volume=23 |issue=5 |title=The sensitivity of soil respiration to soil temperature, moisture, and carbon supply at the global scale |url=https://par.nsf.gov/servlets/purl/10039954 |archive-url=https://web.archive.org/web/20180129004724/https://pdfs.semanticscholar.org/cd03/8a35140615dfe70b706fac68cfde5b5fef31.pdf |url-status=live |archive-date=29 January 2018 |year=2017 |pages=2090–103 |doi=10.1111/gcb.13489 |pmid=27594213 |access-date=4 June 2025 |bibcode=2017GCBio..23.2090H |s2cid=25638073 }} Soil temperature regulates seed germination,{{cite journal |last1=Forcella |first1=Frank |last2=Benech Arnold |first2=Roberto L. |last3=Sanchez |first3=Rudolfo |last4=Ghersa |first4=Claudio M. |journal=Field Crops Research |volume=67 |issue=2 |title=Modeling seedling emergence |url=https://www.academia.edu/81006145 |year=2000 |pages=123–39 |doi=10.1016/S0378-4290(00)00088-5 |bibcode=2000FCrRe..67..123F |access-date=4 June 2025 }} breaking of seed dormancy,{{cite journal |last1=Benech-Arnold |first1=Roberto L. |last2=Sánchez |first2=Rodolfo A. |last3=Forcella |first3=Frank |last4=Kruk |first4=Betina C. |last5=Ghersa |first5=Claudio M. |journal=Field Crops Research |volume=67 |issue=2 |title=Environmental control of dormancy in weed seed banks in soil |url=https://www.academia.edu/106479667 |year=2000 |pages=105–22 |doi=10.1016/S0378-4290(00)00087-3 |bibcode=2000FCrRe..67..105B |access-date=4 June 2025 }}{{cite journal |last1=Herranz |first1=José M. |last2=Ferrandis |first2=Pablo |last3=Martínez-Sánchez |first3=Juan J. |journal=Plant Ecology |volume=136 |issue=1 |title=Influence of heat on seed germination of seven Mediterranean Leguminosae species |url=https://www.researchgate.net/publication/226645015 |year=1998 |pages=95–103 |doi=10.1023/A:1009702318641 |bibcode=1998PlEco.136...95H |s2cid=1145738 |access-date=4 June 2025 }} plant and root growth{{cite journal |last1=McMichael |first1=Bobbie L. |last2=Burke |first2=John J. |journal=HortScience |volume=33 |issue=6 |title=Soil temperature and root growth |url=https://journals.ashs.org/hortsci/downloadpdf/journals/hortsci/33/6/article-p947.xml |year=1998 |pages=947–51 |access-date=4 June 2025 |doi=10.21273/HORTSCI.33.6.947 |archive-url=https://web.archive.org/web/20180712212314/http://hortsci.ashspublications.org/content/33/6/947.full.pdf |archive-date=12 July 2018 |url-status=live }} and the availability of nutrients.{{cite journal |last1=Tindall |first1=James A. |last2=Mills |first2=Harry A. |last3=Radcliffe |first3=David E. |journal=Journal of Plant Nutrition |volume=13 |issue=8 |title=The effect of root zone temperature on nutrient uptake of tomato |url=https://fr.1lib.sk/book/63178226/00e583 |year=1990 |pages=939–56 |doi=10.1080/01904169009364127 |bibcode=1990JPlaN..13..939T |access-date=4 June 2025 }} Soil temperature has important seasonal, monthly and daily variations, fluctuations in soil temperature being much lower with increasing soil depth.{{cite web |url=http://www.halesowenweather.co.uk/soil_temperatures.htm |publisher=Met Office |location=Exeter, United Kingdom |title=Soil temperatures |access-date=4 June 2025 }} Heavy mulching (a type of soil cover) can slow the warming of soil in summer, and, at the same time, reduce fluctuations in surface temperature.{{cite journal |last=Lal |first=Ratan |journal=Plant and Soil |volume=40 |issue=1 |title=Soil temperature, soil moisture and maize yield from mulched and unmulched tropical soils |url=https://fr.1lib.sk/book/37402592/c35515 |year=1974 |pages=129–43 |doi=10.1007/BF00011415 |bibcode=1974PlSoi..40..129L |s2cid=44721938 |access-date=4 June 2025 }}

Most often, agricultural activities must adapt to soil temperatures by:

1. maximizing germination and growth by timing of planting (also determined by photoperiod){{cite book |last1=Ritchie |first1=Joe T. |last2=NeSmith |first2=D. Scott |date=1991 |chapter=Temperature and crop development |title=Modeling plant and soil systems |edition=1st |editor1-first=John |editor1-last=Hanks |editor2-first=Joe T. |editor2-last=Ritchie |publisher=American Society of Agronomy |location=Madison, Wisconsin |pages=5–29 |isbn=978-0-89118-106-4 |chapter-url=https://www.researchgate.net/publication/286506189 |access-date=4 June 2025 }}
2. optimizing use of anhydrous ammonia by applying to soil below {{convert|10|°C|°F|abbr=on}}{{cite journal|last1=Vetsch |first1=Jeffrey A. |last2=Randall |first2=Gyles W. |journal=Agronomy Journal |volume=96 |issue=2 |title=Corn production as affected by nitrogen application timing and tillage |url=https://nue.okstate.edu/Index_Publications/A_split.pdf |year=2004 |pages=502–09 |doi=10.2134/agronj2004.5020 |bibcode=2004AgrJ...96..502V |access-date=4 June 2025 }}
3. preventing heaving and thawing due to frosts from damaging shallow-rooted crops{{cite journal |last1=Holmes |first1=R.M. |last2=Robertson |first2=G.W. |journal=Canadian Journal of Soil Science |volume=40 |issue=2 |title=Soil heaving in alfalfa plots in relation to soil and air temperature |year=1960 |pages=212–18 |doi=10.4141/cjss60-027 |doi-access=free }}
4. preventing damage to desirable soil structure by freezing of saturated soils{{cite journal |last=Dagesse |first=Daryl F. |journal=Canadian Journal of Soil Science |volume=93 |issue=4 |title=Freezing cycle effects on water stability of soil aggregates |year=2013 |pages=473–83 |doi=10.4141/cjss2012-046 |doi-access=free }}
5. improving uptake of phosphorus by plants{{cite journal |last1=Dormaar |first1=Johan F. |last2=Ketcheson |first2=John W. |journal=Canadian Journal of Soil Science |volume=40 |issue=2 |title=The effect of nitrogen form and soil temperature on the growth and phosphorus uptake of corn plants grown in the greenhouse |year=1960 |pages=177–84 |doi=10.4141/cjss60-023 |doi-access=free }}

Soil temperatures can be raised by drying soils{{cite journal |last1=Fuchs |first1=Marcel |last2=Tanner |first2=Champ B. |journal=Journal of Applied Meteorology |volume=6 |issue=5 |title=Evaporation from a drying soil |year=1967 |pages=852–57 |doi=10.1175/1520-0450(1967)006<0852:EFADS>2.0.CO;2 |bibcode=1967JApMe...6..852F |url=https://fr.1lib.sk/book/77923343/e94d60 |access-date=4 June 2025 }} or the use of clear plastic mulches.{{cite journal |last1=Waggoner |first1=Paul E. |last2=Miller |first2=Patrick M. |last3=De Roo |first3=Henry C. |journal=Bulletin of the Connecticut Agricultural Experiment Station |volume=634 |title=Plastic mulching: principles and benefits |url=https://archive.org/details/plasticmulchingp00wagg |year=1960 |pages=1–44 |access-date=4 June 2025 }} Organic mulches slow the warming of the soil.

There are various factors that affect soil temperature, such as water content,{{cite journal |last=Beadle |first=Noel C.W. |journal=Journal of Ecology |volume=28 |issue=1 |title=Soil temperatures during forest fires and their effect on the survival of vegetation |url=http://firearchaeology.com/Direct_Effects_files/Beadle_1940.pdf |year=1940 |pages=180–92 |doi=10.2307/2256168 |access-date=4 June 2025 |jstor=2256168 |bibcode=1940JEcol..28..180B }} soil color,{{cite journal |last1=Post |first1=Donald F. |last2=Fimbres |first2=Adan |last3=Matthias |first3=Allan D. |last4=Sano |first4=Edson E. |last5=Accioly |first5=Luciano |last6=Batchily |first6=A. Karim |last7=Ferreira |first7=Laerte G. |journal=Soil Science Society of America Journal |volume=64 |issue=3 |title=Predicting soil albedo from soil color and spectral reflectance data |url=https://www.researchgate.net/publication/237751086 |year=2000 |pages=1027–34 |doi=10.2136/sssaj2000.6431027x |access-date=4 June 2025 |bibcode=2000SSASJ..64.1027P }} and relief (slope, orientation, and elevation),{{cite journal |last1=Macyk |first1=T.M. |last2=Pawluk |first2=S. |last3=Lindsay |first3=J.D. |journal=Canadian Journal of Soil Science |volume=58 |issue=3 |title=Relief and microclimate as related to soil properties |year=1978 |pages=421–38 |doi=10.4141/cjss78-049 |doi-access=free }} and soil cover (shading and insulation), in addition to air temperature.{{cite journal |last1=Zheng |first1=Daolan |last2=Hunt Jr |first2=E. Raymond |last3=Running |first3=Steven W. |journal=Climate Research |volume=2 |issue=3 |title=A daily soil temperature model based on air temperature and precipitation for continental applications |year=1993 |pages=183–91 |doi=10.3354/cr002183 |bibcode=1993ClRes...2..183Z |url=https://scholarworks.umt.edu/cgi/viewcontent.cgi?article=1329&context=ntsg_pubs |access-date=4 June 2025 }} The color of the ground cover and its insulating properties have a strong influence on soil temperature.{{cite journal |last1=Kang |first1=Sinkyu |last2=Kim |first2=S. |last3=Oh |first3=S. |last4=Lee |first4=Dowon |journal=Forest Ecology and Management |volume=136 |issue=1–3 |title=Predicting spatial and temporal patterns of soil temperature based on topography, surface cover and air temperature |url=https://www.academia.edu/9410216 |year=2000 |pages=173–84 |doi=10.1016/S0378-1127(99)00290-X |bibcode=2000ForEM.136..173K |access-date=4 June 2025 }} Whiter soil tends to have a higher albedo than blacker soil cover, which encourages whiter soils to have lower soil temperatures. The specific heat of soil is the energy required to raise the temperature of soil by 1 °C. The specific heat of soil increases as water content increases, since the heat capacity of water is greater than that of dry soil.{{cite journal |last=Bristow |first=Keith L. |journal=Agricultural and Forest Meteorology |volume=89 |issue=2 |title=Measurement of thermal properties and water content of unsaturated sandy soil using dual-probe heat-pulse probes |url=https://fr.1lib.sk/book/49994701/2839f8 |year=1998 |pages=75–84 |doi=10.1016/S0168-1923(97)00065-8 |access-date=4 June 2025 |bibcode=1998AgFM...89...75B }} The specific heat capacity of pure water is ~ 1 calorie per gram, the specific heat capacity of dry soil is ~ 0.2 calories per gram, hence, the specific heat capacity of wet soil is ~ 0.2 to 1 calories per gram (0.8 to 4.2 kJ per kilogram).{{cite journal |last=Abu-Hamdeh |first=Nidal H. |journal=Biosystems Engineering |volume=86 |issue=1 |title=Thermal properties of soils as affected by density and water content |url=https://www.academia.edu/1319876 |year=2003 |pages=97–102 |doi=10.1016/S1537-5110(03)00112-0 |bibcode=2003BiSyE..86...97A |access-date=4 June 2025 }} Also, a tremendous energy (~584 cal/g or 2442 kJ/kg at 25 °C) is required to evaporate water (known as the heat of vaporization). As such, wet soil usually warms more slowly than dry soil – wet surface soil is typically 3 to 6 °C colder than dry surface soil.{{cite journal |last=Beadle |first=N.C.W. |journal=Journal of Ecology |volume=28 |issue=1 |title=Soil temperatures during forest fires and their effect on the survival of vegetation |url=http://firearchaeology.com/Direct_Effects_files/Beadle_1940.pdf |year=1940 |pages=180–92 |doi=10.2307/2256168 |access-date=4 June 2025 |jstor=2256168 |bibcode=1940JEcol..28..180B }}

Soil heat flux refers to the rate at which heat energy moves through the soil in response to a temperature difference between two points in the soil. The heat flux density is the amount of energy that flows through soil per unit area per unit time and has both magnitude and direction. For the simple case of conduction into or out of the soil in the vertical direction, which is most often applicable the heat flux density is:

: $q\_x\; =\; -\; k\; \backslash frac\{\backslash delta\; T\}\{\backslash delta\; x\}$

In SI units

: $q$ is the heat flux density, in SI the units are W·m⁻²

: $k$ is the soils' conductivity, W·m⁻¹·K⁻¹. The thermal conductivity is sometimes a constant, otherwise an average value of conductivity for the soil condition between the surface and the point at depth is used.

: $\backslash delta\; T$ is the temperature difference (temperature gradient) between the two points in the soil between which the heat flux density is to be calculated. In SI the units are kelvin, K.

: $\backslash delta\; x$ is the distance between the two points within the soil, at which the temperatures are measured and between which the heat flux density is being calculated. In SI the units are meters m, and where x is measured positive downward.

Heat flux is in the direction opposite the temperature gradient, hence the minus sign. That is to say, if the temperature of the surface is higher than at depth x, the negative sign will result in a positive value for the heat flux q, and which is interpreted as the heat being conducted into the soil.

(Source)

Soil temperature is important for the survival and early growth of seedlings.{{cite journal |last=Barney |first=Charles W. |journal=Plant Physiology |volume=26 |issue=1 |title=Effects of soil temperature and light intensity on root growth of loblolly pine seedlings |year=1951 |pages=146–63 |doi=10.1104/pp.26.1.146 |pmid=16654344 |pmc=437627 |url=https://fr.1lib.sk/book/88116933/d68dbe |access-date=4 June 2025 }} Soil temperatures affect the anatomical and morphological character of root systems.{{cite journal |last1=Equiza |first1=Maria A. |last2=Miravé |first2=Juan P. |last3=Tognetti |first3=Jorge A. |journal=Annals of Botany |volume=87 |issue=1 |title=Morphological, anatomical and physiological responses related to differential shoot vs. root growth inhibition at low temperature in spring and winter wheat |url=https://www.academia.edu/47617502 |year=2001 |pages=67–76 |doi=10.1006/anbo.2000.1301 |access-date=4 June 2025 }} All physical, chemical, and biological processes in soil and roots are affected in particular because of the increased viscosities of water and protoplasm at low temperatures.{{cite journal |last1=Babalola |first1=Olubukola |author-link=Olubukola Babalola |last2=Boersma |first2=Larry |last3=Youngberg |first3=Chester T. |year=1968 |title=Photosynthesis and transpiration of Monterey pine seedlings as a function of soil water suction and soil temperature |url=https://fr.1lib.sk/book/71114185/c9c67a |journal=Plant Physiology |volume=43 |issue=4 |pages=515–21 |doi=10.1104/pp.43.4.515 |pmc=1086880 |pmid=16656800 |access-date=4 June 2025 }} In general, climates that do not preclude survival and growth of white spruce above ground are sufficiently benign to provide soil temperatures able to maintain white spruce root systems. In some northwestern parts of the range, white spruce occurs on permafrost sites{{cite journal |last=Gill |first=Don |journal=Canadian Journal of Earth Sciences |volume=12 |issue=2 |title=Influence of white spruce trees on permafrost-table microtopography, Mackenzie River Delta |url=https://fr.1lib.sk/book/64054799/95f935 |year=1975 |pages=263–72 |doi=10.1139/e75-023 |access-date=4 June 2025 |bibcode=1975CaJES..12..263G }} and although young unlignified roots of conifers may have little resistance to freezing,{{cite journal |last1=Coleman |first1=Mark D. |last2=Hinckley |first2=Thomas M. |last3=McNaughton |first3=Geoffrey |last4=Smit |first4=Barbara A. |journal=Canadian Journal of Forest Research |volume=22 |issue=7 |title=Root cold hardiness and native distribution of subalpine conifers |url=https://www.researchgate.net/publication/235695452 |year=1992 |pages=932–38 |doi=10.1139/x92-124 |access-date=4 June 2025 }} the root system of containerized white spruce was not affected by exposure to a temperature of 5 to 20 °C.{{cite journal |last1=Binder |first1=Wolfgang D. |last2=Fielder |first2=Peter |journal=New Forests |volume=9 |issue=3 |title=Heat damage in boxed white spruce (Picea glauca [Moench.] Voss) seedlings: its pre-planting detection and effect on field performance |url=https://www.academia.edu/22073783 |year=1995 |pages=237–59 |doi=10.1007/BF00035490 |bibcode=1995NewFo...9..237B |s2cid=6638289 |access-date=4 June 2025 }}

Optimum temperatures for tree root growth range between 10 °C and 25 °C in general and for spruce in particular.{{cite journal |last1=Landhäusser |first1=Simon M. |last2=DesRochers |first2=Annie |last3=Lieffers |first3=Victor J. |journal=Canadian Journal of Forest Research |volume=31 |issue=11 |title=A comparison of growth and physiology in Picea glauca and Populus tremuloides at different soil temperatures |url=https://www.academia.edu/15511627 |year=2001 |pages=1922–29 |doi=10.1139/x01-129 |access-date=4 June 2025 }} In 2-week-old white spruce seedlings that were then grown for 6 weeks in soil at temperatures of 15 °C, 19 °C, 23 °C, 27 °C, and 31 °C; shoot height, shoot dry weight, stem diameter, root penetration, root volume, and root dry weight all reached maxima at 19 °C.{{cite journal |last1=Heninger |first1=Ronald L. |last2=White |first2=D.P. |journal=Forest Science |volume=20 |issue=4 |title=Tree seedling growth at different soil temperatures |year=1974 |pages=363–67 |doi=10.1093/forestscience/20.4.363 |doi-access=free }}

However, whereas strong positive relationships between soil temperature (5 °C to 25 °C) and growth have been found in trembling aspen and balsam poplar, white and other spruce species have shown little or no changes in growth with increasing soil temperature.{{cite journal |last1=Tryon |first1=Peter R. |last2=Chapin |first2=F. Stuart III |journal=Canadian Journal of Forest Research |volume=13 |issue=5 |title=Temperature control over root growth and root biomass in taiga forest trees |year=1983 |pages=827–33 |doi=10.1139/x83-112 |url=https://fr.1lib.sk/book/64094817/3fdc06 |access-date=4 June 2025 }}{{cite journal |last1=Landhäusser |first1=Simon M. |last2=Silins |first2=Uldis |last3=Lieffers |first3=Victor J. |last4=Liu |first4=Wei |journal=Scandinavian Journal of Forest Research |volume=18 |issue=5 |title=Response of Populus tremuloides, Populus balsamifera, Betula papyrifera and Picea glauca seedlings to low soil temperature and water-logged soil conditions |url=https://www.researchgate.net/publication/41107813 |year=2003 |pages=391–400 |doi=10.1080/02827580310015044 |bibcode=2003SJFR...18..391L |s2cid=85973742 |access-date=4 June 2025 }}{{cite journal |last1=Turner |first1=N.C. |last2=Jarvis |first2=Paul G. |journal=Journal of Applied Ecology |volume=12 |issue=2 |title=Photosynthesis in Sitka spruce (Picea sitchensis (Bong.) Carr. IV. Response to soil temperature |jstor=2402174 |year=1975 |pages=561–76 |doi=10.2307/2402174 |bibcode=1975JApEc..12..561T |url=https://www.researchgate.net/publication/273073866 |access-date=4 June 2025 }}{{cite journal |last1=Day |first1=Tolly A. |last2=DeLucia |first2=Evan H. |last3=Smith |first3=William K. |year=1990 |title=Effect of soil temperature on stem flow, shoot gas exchange and water potential of Picea engelmannii (Parry) during snowmelt |jstor=4219453 |journal=Oecologia |volume=84 |issue=4 |pages=474–81 |doi=10.1007/bf00328163 |bibcode=1990Oecol..84..474D |pmid=28312963 |s2cid=2181646 |url=https://fr.1lib.sk/book/91560536/55fb8c |access-date=4 June 2025 }} Such insensitivity to soil low temperature may be common among a number of western and boreal conifers.{{cite journal |last=Green |first=D. Scott |year=2004 |title=Describing condition-specific determinants of competition in boreal and sub-boreal mixedwood stands |journal=Forestry Chronicle |volume=80 |issue=6 |pages=736–42 |doi=10.5558/tfc80736-6 |url=https://pubs.cif-ifc.org/doi/pdf/10.5558/tfc80736-6 |access-date=4 June 2025 }}

Soil temperatures are increasing worldwide under the influence of present-day global climate warming, with opposing views about expected effects on carbon capture and storage and feedback loops to climate change{{cite journal |last1=Davidson |first1=Eric A. |last2=Janssens |first2=Ivan A. |year=2006 |title=Temperature sensitivity of soil carbon decomposition and feedbacks to climate change |url=https://www.nature.com/articles/nature04514.pdf |archive-url=https://web.archive.org/web/20180409043601/https://pdfs.semanticscholar.org/a821/54357b012bd2b159d5edea949ffc2398561d.pdf |url-status=live |archive-date=9 April 2018 |journal=Nature |volume=440 |issue=7081 |pages=165–73 |doi=10.1038/nature04514 |pmid=16525463 |access-date=4 June 2025 |bibcode=2006Natur.440..165D |s2cid=4404915 }} Most threats are about permafrost thawing and attended effects on carbon destocking{{cite journal |last1=Schaefer |first1=Kevin |last2=Zhang |first2=Tingjun |last3=Bruhwiler |first3=Lori |last4=Barrett |first4=Andrew P. |year=2011 |title=Amount and timing of permafrost carbon release in response to climate warming |url=https://www.tandfonline.com/doi/pdf/10.1111/j.1600-0889.2010.00527.x |journal=Tellus B |volume=63 |issue=2 |pages=165–80 |doi=10.1111/j.1600-0889.2011.00527.x |access-date=4 June 2025 |bibcode=2011TellB..63..165S }} and ecosystem collapse.{{cite journal |last1=Jorgenson |first1=M. Torre |last2=Racine |first2=Charles H. |last3=Walters |first3=James C. |last4=Osterkamp |first4=Thomas E. |year=2001 |title=Permafrost degradation and ecological changes associated with a warming climate in Central Alaska |journal=Climatic Change |volume=48 |issue=4 |pages=551–79 |doi=10.1023/A:1005667424292 |bibcode=2001ClCh...48..551J |citeseerx=10.1.1.420.5083|s2cid=18135860 |url=https://www.researchgate.net/publication/226137241 |access-date=4 June 2025 }}

{{Main|Soil color}}

Soil colour is often the first impression one has when viewing soil. Striking colours and contrasting patterns are especially noticeable. The Red River of the South carries sediment eroded from extensive reddish soils like Port Silt Loam in Oklahoma. The Yellow River in China carries yellow sediment from eroding loess soils. Mollisols in the Great Plains of North America are darkened and enriched by organic matter. Podsols in boreal forests have highly contrasting layers due to acidity and leaching.

In general, color is determined by the organic matter content, drainage conditions, and degree of oxidation. Soil color, while easily discerned, has little use in predicting soil characteristics.{{sfn|Donahue|Miller|Shickluna|1977|p=71}} It is of use in distinguishing boundaries of horizons within a soil profile,{{cite web |url=https://blogs.egu.eu/divisions/sss/2014/03/30/soil-color-never-lies/ |publisher=European Geosciences Union |title=Soil color never lies |access-date=4 June 2025 }} determining the origin of a soil's parent material,{{cite journal |last1=Viscarra Rossel |first1=Raphael A. |last2=Cattle |first2=Stephen R. |last3=Ortega |first3=A. |last4=Fouad |first4=Youssef |journal=Geoderma |volume=150 |issue=3–4 |title=In situ measurements of soil colour, mineral composition and clay content by vis–NIR spectroscopy |year=2009 |pages=253–66 |citeseerx=10.1.1.462.5659 |doi=10.1016/j.geoderma.2009.01.025|bibcode=2009Geode.150..253V |url=https://www.academia.edu/18500720 |access-date=4 June 2025 }} as an indication of wetness and waterlogged conditions,{{cite journal |last1=Blavet |first1=Didier |last2=Mathe |first2=E. |last3=Leprun |first3=Jean-Claude |journal=Catena |volume=39 |issue=3 |title=Relations between soil colour and waterlogging duration in a representative hillside of the West African granito-gneissic bedrock |url=https://fr.1lib.sk/book/50141324/6c95aa |year=2000 |pages=187–210 |doi=10.1016/S0341-8162(99)00087-9 |bibcode=2000Caten..39..187B |access-date=4 June 2025 }} and as a qualitative means of measuring organic,{{cite journal |last1=Shields |first1=J.A. |last2=Paul |first2=Eldor A. |last3=St. Arnaud |first3=Roland J. |last4=Head |first4=W.K. |journal=Canadian Journal of Soil Science |volume=48 |issue=3 |title=Spectrophotometric measurement of soil color and its relationship to moisture and organic matter |year=1968 |pages=271–80 |doi=10.4141/cjss68-037 |doi-access=free }} iron oxide{{cite journal |last1=Barrón |first1=Vidal |last2=Torrent |first2=José |journal=Journal of Soil Science |volume=37 |issue=4 |title=Use of the Kubelka-Munk theory to study the influence of iron oxides on soil colour |url=https://www.uco.es/organiza/departamentos/decraf/pdf-edaf/JSS1986.pdf |year=1986 |pages=499–510 |doi=10.1111/j.1365-2389.1986.tb00382.x |access-date=4 June 2025 }} and clay contents of soils. Color is recorded in the Munsell color system as for instance 10YR3/4 Dusky Red, with 10YR as hue, 3 as value and 4 as chroma. Munsell color dimensions (hue, value and chroma) can be averaged among samples and treated as quantitative parameters, displaying significant correlations with various soil{{cite journal |last1=Ponge |first1=Jean-François |last2=Chevalier |first2=Richard |last3=Loussot |first3=Philippe |journal=Soil Science Society of America Journal |volume=66 |issue=6 |title=Humus Index: an integrated tool for the assessment of forest floor and topsoil properties |url=https://www.researchgate.net/publication/240789573 |year=2002 |pages=1996–2001 |doi=10.2136/sssaj2002.1996 |access-date=4 June 2025 |bibcode=2002SSASJ..66.1996P |s2cid=92303060 }} and vegetation properties.{{cite journal |last1=Maurel |first1=Noelie |last2=Salmon |first2=Sandrine |last3=Ponge |first3=Jean-François |last4=Machon |first4=Nathalie |last5=Moret |first5=Jacques |last6=Muratet |first6=Audrey |journal=Biological Invasions |volume=12 |issue=6 |title=Does the invasive species Reynoutria japonica have an impact on soil and flora in urban wastelands? |url=https://www.researchgate.net/publication/234058727 |year=2010 |pages=1709–19 |doi=10.1007/s10530-009-9583-4 |bibcode=2010BiInv..12.1709M |s2cid=2936621 |access-date=4 June 2025 }}

Soil color is primarily influenced by soil mineralogy. Many soil colours are due to various iron minerals. The development and distribution of colour in a soil profile result from chemical and biological weathering, especially redox reactions. As the primary minerals in soil parent material weather, the elements combine into new and colourful compounds. Iron forms secondary minerals of a yellow or red colour,{{cite journal |last1=Davey |first1=Bryan G. |last2=Russell |first2=James D. |last3=Wilson |first3=M. Jeff |journal=Geoderma |volume=14 |issue=2 |title=Iron oxide and clay minerals and their relation to colours of red and yellow podzolic soils near Sydney, Australia |url=https://fr.1lib.sk/book/48380549/6b22c3 |year=1975 |pages=125–38 |doi=10.1016/0016-7061(75)90071-3 |access-date=4 June 2025 |bibcode=1975Geode..14..125D }} organic matter decomposes into black and brown humic compounds,{{cite journal |last=Anderson |first=Darwin W. |journal=Journal of Soil Science |volume=30 |issue=1 |title=Processes of humus formation and transformation in soils of the Canadian Great Plains |year=1979 |pages=77–84 |doi=10.1111/j.1365-2389.1979.tb00966.x |url=https://www.academia.edu/75160361 |access-date=4 June 2025 }} and manganese{{cite journal |last1=Vodyanitskii |first1=Yury N. |last2=Vasil'ev |first2=A.A. |last3=Lessovaia |first3=Sofia N. |last4=Sataev |first4=E.F. |last5=Sivtsov |first5=Anatolii V. |journal=Eurasian Soil Science |volume=37 |issue=6 |title=Formation of manganese oxides in soils |url=https://www.researchgate.net/publication/279708542 |year=2004 |pages=572–84 |access-date=4 June 2025 }} and sulfur{{cite book |last1=Fanning |first1=D.S. |last2=Rabenhorst |first2=M.C. |last3=Bigham |first3=J.M. |date=1993 |chapter=Colors of acid sulfate soils |title=Soil color |edition=1st |editor1-first=Jerry M. |editor1-last=Bigham |editor2-first=Edward J. |editor2-last=Ciolkosz |publisher=Soil Science Society of America |location=Fitchburg, Wisconsin |pages=91–108 |isbn=978-0-89118-926-8 |chapter-url=https://fr.1lib.sk/book/98253675/24bbfd |access-date=4 June 2025 }} can form black mineral deposits. These pigments can produce various colour patterns within a soil. Aerobic conditions produce uniform or gradual colour changes, while reducing environments (anaerobic) result in rapid colour flow with complex, mottled patterns and points of colour concentration.{{cite web |url=https://www.nrcs.usda.gov/sites/default/files/2022-11/color-of-soil.pdf |publisher=United States Department of Agriculture – Natural Resources Conservation Service |title=The color of soil |access-date=4 June 2025 }}

{{main|Soil resistivity}}

Soil resistivity is a measure of a soil's ability to retard the conduction of an electric current. The electrical resistivity of soil can affect the rate of corrosion of metallic structures in contact with the soil.{{cite journal |last1=Cole |first1=Ivan S. |last2=Marney |first2=Donavan |journal=Corrosion Science |volume=56 |title=The science of pipe corrosion: a review of the literature on the corrosion of ferrous metals in soils |year=2012 |pages=5–16 |doi=10.1016/j.corsci.2011.12.001 |bibcode=2012Corro..56....5C |url=https://fr.1lib.sk/book/48872456/6b99cd |access-date=5 June 2025 }} Higher moisture content or increased electrolyte concentration can lower resistivity and increase conductivity, thereby increasing the rate of corrosion.{{cite journal |last1=Noor |first1=Ehteram A. |last2=Al-Moubaraki |first2=Aisha |journal=Arabian Journal for Science and Engineering |volume=39 |issue=7 |title=Influence of soil moisture content on the corrosion behavior of X60 steel in different soils |url=https://www.researchgate.net/publication/272039484 |year=2014 |pages=5421–35 |doi=10.1007/s13369-014-1135-2 |s2cid=137468323 |access-date=5 June 2025 }}{{cite journal |last1=Amrheln |first1=Christopher |last2=Strong |first2=James E. |last3=Mosher |first3=Paul A. |journal=Environmental Science and Technology |volume=26 |issue=4 |title=Effect of deicing salts on metal and organic matter mobility in roadside soils |url=https://fr.1lib.sk/book/53898229/1d52e0 |year=1992 |pages=703–09 |doi=10.1021/es00028a006 |access-date=5 June 2025 |bibcode=1992EnST...26..703A }} Soil resistivity values typically range from about 1 to 100000 Ω·m, extreme values being for saline soils and dry soils overlaying crystalline rocks, respectively.{{cite journal |last1=Samouëlian |first1=Anatja |last2=Cousin |first2=Isabelle |last3=Tabbagh |first3=Alain |last4=Bruand |first4=Ary |last5=Richard |first5=Guy |journal=Soil and Tillage Research |volume=83 |issue=2 |title=Electrical resistivity survey in soil science: a review |url=https://www.researchgate.net/publication/222649758 |year=2005 |pages=173–93 |doi=10.1016/j.still.2004.10.004 |bibcode=2005STilR..83..173S |access-date=5 June 2025 |citeseerx=10.1.1.530.686 |s2cid=53615967 }}

• Soil liquefaction
• Soil matrix

{{Reflist}}

{{refbegin}}

• {{cite book |title=Soils: An Introduction to Soils and Plant Growth |last1=Donahue |first1=Roy Luther |last2=Miller |first2=Raymond W. |last3=Shickluna |first3=John C. |year=1977 |publisher=Prentice-Hall |isbn=978-0-13-821918-5 |url=https://archive.org/details/soilsintroductio00dona |access-date=5 June 2025 }}
• {{cite book|title=Arizona Master Gardener|url=https://fr.1lib.sk/book/21179861/f106c9 |publisher=Cooperative Extension, College of Agriculture, University of Arizona |access-date=5 June 2025 }}
• {{cite book |title=Soil: The Yearbook of Agriculture 1957 |editor-last=Stefferud |editor-first=Alfred |year=1957 |publisher=United States Department of Agriculture |url=https://archive.org/details/yoa1957/mode/1up?view=theater |oclc=704186906 |access-date=5 June 2025 }}
• {{harvc |name-list-style=harv |last=Kellogg |first=Charles E. |chapter=We Seek; We Learn |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n17/mode/1up }}
• {{harvc |name-list-style=harv |last=Simonson |first=Roy W. |chapter=What Soils Are |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n34/mode/1up }}
• {{harvc |name-list-style=harv |last=Russell |first=M.B. |chapter=Physical Properties |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n49/mode/1up }}
• {{harvc |name-list-style=harv |last=Richards |first=L.A. |last2=Richards |chapter=Soil Moisture |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n68/mode/1up }}
• {{harvc |name-list-style=harv |last=Wadleigh |first=C.H. |chapter=Growth of Plants |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n57/mode/1up }}
• {{harvc |name-list-style=harv |last=Allaway |first=W.H. |chapter=pH, Soil Acidity, and Plant Growth |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n87/mode/1up }}
• {{harvc |name-list-style=harv |last=Coleman |first=N.T. |last2=Mehlich |chapter=The Chemistry of Soil pH |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n92/mode/1up }}
• {{harvc |name-list-style=harv |last=Dean |first=L.A. |chapter=Plant Nutrition and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n100/mode/1up }}
• {{harvc |name-list-style=harv |last=Allison |first=Franklin E. |chapter=Nitrogen and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n105/mode/1up |oclc=704186906}}
• {{harvc |name-list-style=harv |last=Olsen |first=Sterling R. |last2=Fried |chapter=Soil Phosphorus and Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n115/mode/1up }}
• {{harvc |name-list-style=harv |last=Reitemeier |first=R.F. |chapter=Soil Potassium and Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n123/mode/1up }}
• {{harvc |name-list-style=harv |last=Jordan |first=Howard V. |last2=Reisenauer |chapter=Sulfur and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n129/mode/1up }}
• {{harvc |name-list-style=harv |last=Holmes |first=R.S. |last2=Brown |chapter=Iron and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n133/mode/1up }}
• {{harvc |name-list-style=harv |last=Seatz |first=Lloyd F. |last2=Jurinak |chapter=Zinc and Soil Fertility|in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n138/mode/1up }}
• {{harvc |name-list-style=harv |last=Russel |first=Darrell A. |chapter=Boron and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n145/mode/1up |oclc=704186906}}
• {{harvc |name-list-style=harv |last=Reuther |first=Walter |chapter=Copper and Soil Fertility |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n154/mode/1up |oclc=704186906}}
• {{harvc |name-list-style=harv |last=Sherman |first=G. Donald |chapter=Manganese and Soil Fertility|in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n162/mode/1up }}
• {{harvc |name-list-style=harv |last=Stout |first=P.R. |last2=Johnson |chapter=Trace Elements |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n167/mode/1up }}
• {{harvc |name-list-style=harv |last=Broadbent |first=F.E. |chapter=Organic Matter |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n179/mode/1up }}
• {{harvc |name-list-style=harv |last=Clark |first=Francis E. |chapter=Living Organisms in the Soil |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n185/mode/1up }}
• {{harvc |name-list-style=harv |last=Flemming |first=Walter E. |chapter=Soil Management and Insect Control |in=Stefferud |year=1957 |url=//archive.org/stream/yoa1957#page/n367/mode/1up }}

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Category:Soil