1. Soil Quality: The view through the prism of Soils 101 D.W. Johnson Natural Resources and Environmental Science University of Nevada, Reno

2. Soil Quality: Who or What defines it? Soil Scientists?Soil Scientists? Plants?Plants? Water quality?Water quality? Lawyers?Lawyers? Farmers?Farmers? Conservationists?Conservationists? Will one definition fit all? Not likely Will the various definitions conflict? Almost certainly

3. Factors of soil formation You cannot modify parent material, climate, or timeYou cannot modify parent material, climate, or time You can modify biota (vegetation easily, microbes less easily) and, with some effort, topographyYou can modify biota (vegetation easily, microbes less easily) and, with some effort, topography

4. SOIL ORDERS (12 major units of classification according to the US 10th Approximation) Alfisols: Clay migration, moderately high %BS Andisols: Volcanic parent material, high P fixation Aridisols:Arid soils, high in salts and pH Entisols: Not well-developed even after long periods (can occur anywhere) Gelisols: Permafrost Histosols: Soils formed from organic matter (peats and mucks) Inceptisols:Still forming, water is available for soil formation Mollisols:Organic-rich A horizons, %BS usually > 50% Oxisols: Highly-weathered (e.g., tropical rainforest) Spodosols: Fe, Al, and organic matter transport, whitish E Horizon (e.g., boreal forest) Ultisols:Clay transport like Alfisols, but much more acidic; higher temperature; often highly weathered (e.g., Southeastern U.S.) Vertisols: Mixed soils; Swelling clays, frost, etc cause lower horizons to mix with upper horizons; Often characterized by cracks

5. The central concept of Alfisols is that of soils that have an argillic, a kandic, or a natric horizon and a base saturation of 35% or greater. They typically have an ochric epipedon, but may have an umbric epipedon. They may also have a petrocalcic horizon, a fragipan or a duripan http://soils.usda.gov/technical/classification/orders/alfisols.html. Alfisols: Relatively high base saturation; not organic rich; evidence of clay transport

6. The central concept of Andisols is that of soils dominated by short- range-order minerals. They include weakly weathered soils with much volcanic glass as well as more strongly weathered soils. Hence the content of volcanic glass is one of the characteristics used in defining andic soil properties. Materials with andic soil properties comprise 60 percent or more of the thickness between the mineral soil surface or the top of an organic layer with andic soil properties and a depth of 60 cm or a root limiting layer if shallower. http://soils.usda.gov/technical/classification/orders/andisols.html. Andisols: Soils derived major properties from volcanic parent material. High P fixation. Many soils locally derived from andesite are “andic”

7. The central concept of Aridisols is that of soils that are too dry for mesophytic plants to grow. They have either: (1) an aridic moisture regime and an ochric or anthropic epipedon and one or more of the following with an upper boundry within 100 cm of the soil surface: a calcic, cambic, gypsic, natric, petrocalcic petrogypsic, or a salic horizon or a duripan or an argillic horizon, or (2)A salic horizon and saturation with water within 100 cm of the soil surface for one month or more in normal years. An aridic moisture regime is one that in normal years has no water available for plants for more than half the cumulative time that the soil temperature at 50 cm below the surface is >5° C. and has no period as long as 90 consecutive days when there is water available for plants while the soil temperature at 50 cm is continuously >8° C http://soils.usda.gov/technical/classification/orders/aridisols.html. Aridisols: Arid soils; Low in organic matter; high in salts and pH

8. The central concept of Entisols is that of soils that have little or no evidence of development of pedogenic horizons. Many Entisols have an ochric epipedon and a few have an anthropic epipedon. Many are sandy or very shallow http://soils.usda.gov/technical/classification/orders/aridisols.html. Entisols: Leftovers; Not well-developed even after long periods (can occur anywhere )

9. The central concept of Gelisols is that of soils that have permafrost within 100 cm of the soil surface and/or have gelic materials within 100 cm of the soil surface and have permafrost within 200 cm. Gelic materials are mineral or organic soil materials that have evidence of cryoturbation (frost churning) and/or ice segeration in the active layer (seasonal thaw layer) and/or the upper part of the permafrost http://soils.usda.gov/technical/classification/orders/gelisols.html. Gelisols: permafrost

10. The central concept of Histosols is that of soils that are dominantly organic. They are mostly soils that are commonly called bogs, moors, or peats and mucks. A soil is classified as Histosols if it does not have permafrost and is dominated by organic soil materials. http://soils.usda.gov/technical/classification/orders/histosols.html. Histosols: Soils formed from organic matter (peats and mucks)

11. The central concept of Inceptisols is that of soils of humid and subhumid regions that have altered horizons that have lost bases or iron and aluminum but retain some weatherable minerals. They do not have an illuvial horizon enriched with either silicate clay or with an amorphous mixture of aluminum and organic carbon. The Inceptisols may have many kinds of diagnostic horizons, but argillic, natric kandic, spodic and oxic horizons are excluded. http://soils.usda.gov/technical/classification/orders/histosols.html. Inceptisols: Still forming; Water is available for soil formation (e.g., glaciated soils). Common in the Sierra Nevada

12. The central concept of Mollisols is that of soils that have a dark colored surface horizon and are base rich. Nearly all have a mollic epipedon. Many also have an argillic or natric horizon or a calcic horizon. A few have an albic horizon. Some also have a duripan or a petrocalic horizon. http://soils.usda.gov/technical/classification/orders/mollisols.html. Mollisols: Brown-black surface horizons; High in organic matter, vermiculite or smectite clays; Base saturation usually > 50% (e.g., Iowa farm soils) Most extensive in the US (25%), present in the Great Basin at higher elevations

13. The central concept of Oxisols is that of soils of the tropical and subtropical regions. They have gentle slopes on surfaces of great age. They are mixtures of quartz, kaolin, free oxides, and organic matter. For the most part they are nearly featureless soils without clearly marked horizons. Differences in properties with depth are so gradual that horizon boundaries are generally arbitrary.. http://soils.usda.gov/technical/classification/orders/oxisols.html. Oxisols: Highly-weathered; Only quartz, kaolinite, and Fe and Al oxides left (e.g., tropical rainforest)

14. The central concept of Spodosols is that of soils in which amorphous mixtures of organic matter and aluminum, with or without iron, have accumulated. In undisturbed soils there is normally an overlying eluvial horizon, generally gray to light gray in color, that has the color of more or less uncoated quartz. Most Spodosols have little silicate clay. The particle-size class is mostly sandy, sandy-skeletal, coarse-loamy, loamy, loamy- skeletal, or coarse-silty http://soils.usda.gov/technical/classification/orders/spodosols.html. Spodosols: Evidence of Fe, Al, and organic matter transport; Often a whitish E Horizon (e.g., boreal forest)

15. The central concept of Ultisols is that of soils that have a horizon that contains an appreciable amount of translocated silicate clay (an argillic or kandic horizon) and few bases (base saturation less than 35 percent). Base saturation in most Ultisols decreases with depth. http://soils.usda.gov/technical/classification/orders/ultisols.html. Ultisols: Clay transport like Alfisols, but much more acidic. Higher temperature; Often highly weathered (e.g., Southeastern U.S.)

16. The central concept of Vertisols is that of soils that have a high content of expending clay and that have at some time of the year deep wide cracks. They shrink when drying and swell when they become wetter. http://soils.usda.gov/technical/classification/orders/vertisols.html. Vertisols: Mixed soils; Swelling clays, frost, etc cause lower horizons to mix with upper horizons; Often characterized by cracks. Present locally, San Rafael park

17. Basic Soil Physical Properties Texture: particle size distribution (sand, silt, clay)Texture: particle size distribution (sand, silt, clay) Structure: arrangement of particles (blocky, single grained, massive, platy…)Structure: arrangement of particles (blocky, single grained, massive, platy…) Coarse fragments/rocks: > 2mmCoarse fragments/rocks: > 2mm Bulk density: soil weight in g cm -3Bulk density: soil weight in g cm -3 Porosity: inversely proportional to bulk densityPorosity: inversely proportional to bulk density Water properties: field capacity, permanent wilting percentage, available water capacity, hydraulic conductivityWater properties: field capacity, permanent wilting percentage, available water capacity, hydraulic conductivity You cannot modify texture or coarse fragmentsYou cannot modify texture or coarse fragments You can modify structure, bulk density, porosity, water propertiesYou can modify structure, bulk density, porosity, water properties

18. Textural Triangle Terms like “sandy loam” actually mean something specific relative to the fine earth fraction (that is, the fraction of soil that passes through a 2 mm sieve). Image from: http://en.wikipedia.org/wiki/Soil_texture

19. Image: Courtesy of NASA, Soil Science Education Home Page http://ltpwww.gsfc.nasa.gov/globe/pvg/prop1.htm, accessed 14 Feb 2008.http://ltpwww.gsfc.nasa.gov/globe/pvg/prop1.htm Soil structure

20. Soil Water Increasing soil water content -1x10 6 -1x10 5 -1500 kPa -33 kPa 0 Permanent Wilting Percentage Available Water Capacity Field Moisture Capacity Saturation Oven Dry Air Dry Soil Water Potential Plant Available Water Current Soil Moisture UnavailableWater

22. Soil moisture release curve: A plot of soil moisture vs the tension at which it is held Notice that the sandy soil holds less moisture at a given tension than the loamy or clay soil do This is because the sandy soil has fewer fine pores Soil water (Ө) Soil moisture tension (kPa) -1500 (PWP) -33 (FMC) Sandy Loamy Clayey

23. High clay soils hold more total water than coarser textured soils However, less of the water in high clay soils is available to plants (lower Available Water Capacity) Thus, loamy soils have the best characteristics for holding water for plants. Clay percentage Soil water (Ө) Sandy Loamy Clay Permanent wilting percentage (-1500 kPa) Field moisture capacity (-33 kPa) Available water capacity

24. Compaction Increases bulk density (by definition)Increases bulk density (by definition) Reduces total porosityReduces total porosity Reduces average pore sizeReduces average pore size Reduces infiltrationReduces infiltration Because of reduced pore size, compaction canBecause of reduced pore size, compaction can Decrease plant available water in finer textured soilsDecrease plant available water in finer textured soils Increase plant available water in coarse textured soils (Gomez et al., 2002)Increase plant available water in coarse textured soils (Gomez et al., 2002)

25. Basic Soil Chemical Properties Total C: organic matter + carbonates Total N: mostly organic C:N Ratio: major factor affecting N availability Cation exchange capacity (CEC): permanent charge (clays) and pH-dependent (organic matter) Base saturation: [(Ca 2+ + Mg 2+ + K + + Na + )/CEC] x 100 Adsorbed ortho-P and SO 4 2- : related to sesquioxide concentrations and organic coatings Micronutrients: varying factors affect them You cannot modify permanent charge CEC or sesquioxidesYou cannot modify permanent charge CEC or sesquioxides You can modify organic matter, N, C:N ratio, base saturation, adsorbed ortho-P and SO 4 2-You can modify organic matter, N, C:N ratio, base saturation, adsorbed ortho-P and SO 4 2-

26. Cation Exchange Capacity (CEC) Cation Exchange Capacity (CEC)Sources: 1.Ionizeable H +; Organic matter, clay edgesOrganic matter, clay edges pH-dependent, just as in the case of a weak acid.pH-dependent, just as in the case of a weak acid. 2.Isomorphous substitution in clays: Substitution of Al 3+ for Si 4+ in the tetrahedral layer of claysSubstitution of Al 3+ for Si 4+ in the tetrahedral layer of clays Substitution of Mg 2+ for Al 3+ in the octahedral layer of claySubstitution of Mg 2+ for Al 3+ in the octahedral layer of clay This type of CEC is often referred to as permanent charge CEC because it is not affected by pH.This type of CEC is often referred to as permanent charge CEC because it is not affected by pH.

27. Kaolinite K K K K K K K 1.0 nm Mica (Primary mineral) H+ K K K H+ H+ 1.0 nm Illite (Med. CEC) 0.93 nm Chlorite (Low-Med CEC) ≈1.4 nm Ca Mg H 2 O Ca H 2 O Vermiculite (High CEC, expands/contracts somewhat) Ca Mg H 2 O Ca H 2 O Smectite (or Montmorillonite (High CEC, expands/contracts a lot) SiO 4 Al(OH) 3 ≈1.8 to 4.0 nm 0.72 nm H+ bonding Silicate clays: permanent charge CEC

28. ------------..Na + A simple example: Ca 2+ exchange displaces exchangeable Na + [Ca 2+ ] ------------..Ca 2+ [Na + ] 2 X Na + + Ca 2+  X Ca 2+ + 2Na + Negatively-charged clay Dissolved in soil solution X = exchangeable

29. Cation Exchange Strength of cation adsorption (lyotropic series):Strength of cation adsorption (lyotropic series): Na + < K + = NH 4 + < Mg 2+ = Ca 2+ < Al n+ < H + Adsorption depends on charge density (charge/vol), so increases with valence and decreases with size.Adsorption depends on charge density (charge/vol), so increases with valence and decreases with size. Not all exchangeable ions are Al n+ and H + because mass action allows the others to be present; but at equal soil solution conc's, this will be the order.Not all exchangeable ions are Al n+ and H + because mass action allows the others to be present; but at equal soil solution conc's, this will be the order.

30. Mass action: Displacement of one adsorbed/exchangeable cation by another by competition for sites when the second has a high number of ions in solution (high concentration)Displacement of one adsorbed/exchangeable cation by another by competition for sites when the second has a high number of ions in solution (high concentration) Works even when trying to drive off most strongly absorbed cations like H + and Al 3+Works even when trying to drive off most strongly absorbed cations like H + and Al 3+ This is why fertilization with K +, Mg 2+ and liming (Ca 2+ ) workThis is why fertilization with K +, Mg 2+ and liming (Ca 2+ ) work

31. Al 3+ Ca 2+ Cation Exchange Site Ca 2+ Cation Exchange Site Ca 2+ Ca 2+ Displaces Al 3+ by Mass Action even though Al 3+ is more strongly absorbed pH increases, Al precipitates as gibbsite: Al 3+ + 3OH -  Al(OH) 3

32. Soil organic matter as a source of CEC Temporary (will ultimately decompose)Temporary (will ultimately decompose) Nearly insoluble in water, but soluble in base (high pH)Nearly insoluble in water, but soluble in base (high pH) Contains 30% each of proteins, lignin, complex sugarsContains 30% each of proteins, lignin, complex sugars 50% C and O, 5% N50% C and O, 5% N Very high CEC on a weight basisVery high CEC on a weight basis Develops a net negative charge due to the dissociation of H + fromDevelops a net negative charge due to the dissociation of H + from enolic (-OH), carboxyl (-COOH), and phenolic ( -OH) groups as pH increases (solution H + concentration decreases):enolic (-OH), carboxyl (-COOH), and phenolic ( -OH) groups as pH increases (solution H + concentration decreases):

33. No charge CEC and exch. K + (could be any cation) R-OH 0 + OH - --------> R-O - … K + + H 2 O (R stands for some organic molecule) This leaves a net negative charge on the organic colloid (R-O - ) which attracts cations just as the net negative charge on an isomorphously-substituted clay does.This leaves a net negative charge on the organic colloid (R-O - ) which attracts cations just as the net negative charge on an isomorphously-substituted clay does. Organic matter is the most important source of pH-dependent CEC in soils.Organic matter is the most important source of pH-dependent CEC in soils. pH-dependent CEC on Organic Matter

34. OH O - K + Low pH, sites protonated no CEC High pH (depronotated, cation exchange site) Organic matter : pH-dependent CEC + OH - + H 2 O

35. NRES 322 Soils Measurement of Cation Exchange Capacity (CEC) and Base Saturation (%BS) CEC is measured by applying concentrated ammonium chloride (NH 4 Cl) or ammonium acetate (NH 4 OAc) to the sample to exchange all exchangeable cations with NH 4 + by mass actionCEC is measured by applying concentrated ammonium chloride (NH 4 Cl) or ammonium acetate (NH 4 OAc) to the sample to exchange all exchangeable cations with NH 4 + by mass action The extractant solution is analyzed for Ca 2+, Mg 2+, K +, Na +, and in some cases Al to determine what was on the exchanger.The extractant solution is analyzed for Ca 2+, Mg 2+, K +, Na +, and in some cases Al to determine what was on the exchanger. At that point, one measure of CEC can be made. Then the NH 4 + is displaced by another cation (typically Na + or K + ) by mass action, and NH 4 + is then measured to obtain another estimate of CEC.At that point, one measure of CEC can be made. Then the NH 4 + is displaced by another cation (typically Na + or K + ) by mass action, and NH 4 + is then measured to obtain another estimate of CEC.

36. NRES 322 Soils Measurement of CEC and %BS The usual assumption is that NH 4 + constitutes a negligible proportion of CEC.The usual assumption is that NH 4 + constitutes a negligible proportion of CEC. Exchangeable NH 4 + is often measured separately using concentrated KCl extractant.Exchangeable NH 4 + is often measured separately using concentrated KCl extractant. H + (pH) is not measured on this extractant, either; exchangeable H + is measured another way.H + (pH) is not measured on this extractant, either; exchangeable H + is measured another way. Some soil scientists argue that there is no exchangeable H + on mineral soils; all H + that becomes absorbed onto clay minerals quickly enters the lattice structure and causes clay decomposition to hydrous oxides.Some soil scientists argue that there is no exchangeable H + on mineral soils; all H + that becomes absorbed onto clay minerals quickly enters the lattice structure and causes clay decomposition to hydrous oxides.

37. There are three ways to measure CEC (two from one method and one from another method): 1. Sum of cations Method: The sum of Ca 2+, Mg 2+, K +, Na +, and Al after extraction with 1M NH 4 Cl (a neutral salt which does not buffer pH). The sum of Ca 2+, Mg 2+, K +, Na +, and Al after extraction with 1M NH 4 Cl (a neutral salt which does not buffer pH). CEC by sum of cations, CEC sum, and is measured in the first extractant in Figure 1. CEC by sum of cations, CEC sum, and is measured in the first extractant in Figure 1. In a pure clay system (no organic matter Fe, Al hydrous oxides, of allophane; i.e., no pH-dependent CEC) this represents CEC and cations on the clay minerals (permanent charge CEC). In a pure clay system (no organic matter Fe, Al hydrous oxides, of allophane; i.e., no pH-dependent CEC) this represents CEC and cations on the clay minerals (permanent charge CEC).

39. 2. Effective CEC (CEC eff ) at existing soil pH. This includes the permanent charge CEC plus that portion of pH-dependent CEC that is in effect at existing soil pH.This includes the permanent charge CEC plus that portion of pH-dependent CEC that is in effect at existing soil pH. It is determined from the second extractant in Figure 1, After the 1M NH 4 Cl extraction, the soil is washed with ethanol to remove soluble NH 4 +, and then extracted with 1M NaCl to displace the exchangeable NH 4 +.It is determined from the second extractant in Figure 1, After the 1M NH 4 Cl extraction, the soil is washed with ethanol to remove soluble NH 4 +, and then extracted with 1M NaCl to displace the exchangeable NH 4 +. The extractant is analyzed for NH 4 +.The extractant is analyzed for NH 4 +. Three ways to measure (cont.)

41. 3. Ammonium acetate CEC (CEC OAc ). This includes permanent charge CEC + all pH-dependent CEC. Is is measured by extracting the soil with either ammonium acetate (NH 4 OAc, buffers pH at 7.0). (Figure 2).This includes permanent charge CEC + all pH-dependent CEC. Is is measured by extracting the soil with either ammonium acetate (NH 4 OAc, buffers pH at 7.0). (Figure 2). Then the same produre is followed as for the neutral salt CEC.Then the same produre is followed as for the neutral salt CEC. Note: exchangeable Al should be measured separately because Al precipitates as Al(OH) 3 at high pHNote: exchangeable Al should be measured separately because Al precipitates as Al(OH) 3 at high pH Three ways to measure (cont.)

42. Soil Sample Extractant 1M NH OAc Buffers pH at 7 4 NH displaces exchangeable cations 4 + Analyze for Ca, K, Mg, and Na ; this gives exchangeable cations except for Al. 2+ 3+ + + Soil Sample Extractant 1M NaCl Na displaces exchangeable NH + + 4 Analyze for NH ; this gives CEC + 4 Step 1. Displace exchangeable cations with NH 4 + Step 2. Displace exchangeable NH 4 + with Na + Figure 2. Measurement of exchangeable cations and CEC buffering pH at 7 using ammonium acetate. pH 7 - - - - - - - - -- Ca -- Mg -- K -- Na -- Al -- H 2+ + + + 3+ + NH + 4 + Na + - - - - - - - - -- NH + 4 + 4 + 4 + 4 + 4 + 4 - - - - - - - - -- Ca -- Mg -- K -- Na -- Al -- H 2+ + + + 3+ + NH + 4 - - - - - - - - -- Na + + + + + + Extractant (Exchangeable Bases only; Al precipitates) Extractant (CEC)

43. Permanent Charge CEC pH-dependent CEC CEC eff CEC OAc CEC sum : Measured as the sum of Ca + Mg + K + Na + Al extracted with ammonium chloride in the first extraction in Figure 1 CEC eff : Measured with ammonium chloride, neutral salt, after second extraction in Fig 1 CEC OAc : Measured with ammonium acetate at pH 7 in Figure 2 Figure 3. Types of CEC depend on how it is measured CEC sum

44. Base Saturation Base Cation Saturation Percentage (BCSP) (often stated as simply base saturation) BCSPis defined as the sum of exchangeable base cations (Ca 2+, Mg 2+, K +, and Na + ) divided by CEC. It is usually expressed as a percentage of CEC thus: BS (%) = Ca + Mg + K + Na CEC x100 CEC x100

45. Base Saturation Since CEC can be measured in different ways, BCSP will vary with the method used, and must be specified. Since CEC can be measured in different ways, BCSP will vary with the method used, and must be specified. For a soil with a given amount of exchangeable bases, % Base saturation calculated from CEC sum will be greater than that calculated from CEC eff which will be greater than that calculated from CEC tot because more of the potential acidity on the pH- dependen CEC is counted as CEC (i.e., CEC sum < CEC eff < CEC tot ). For a soil with a given amount of exchangeable bases, % Base saturation calculated from CEC sum will be greater than that calculated from CEC eff which will be greater than that calculated from CEC tot because more of the potential acidity on the pH- dependen CEC is counted as CEC (i.e., CEC sum < CEC eff < CEC tot ). The example in Figure 4 shows how this might occur. In each case, the base cations are the same (6 cmol c kg -1 ); only the measure of CEC (the denominator) changes. The example in Figure 4 shows how this might occur. In each case, the base cations are the same (6 cmol c kg -1 ); only the measure of CEC (the denominator) changes.

46. Base Cations Ca 2+ + Mg 2+ + K + + Na + = 6 cmol c kg -1 Acid cations Al n+ = 1 cmol c kg -1 H + = 3 cmol c kg -1 CEC eff = 8 cmol c kg -1 CEC OAc = 10 cmol c kg -1 Figure 4. Base saturation value depends on which CEC measure is used CEC sum = 7 cmol c kg -1 %BS sum = __________________________ Ca 2+ + Mg 2+ + K + + Na + CEC sum = Ca 2+ + Mg 2+ + K + + Na + Ca 2+ + Mg 2+ + K + + Na + + Al n+ ________________________ =X 100 6767 =85% %BS eff = Ca 2+ + Mg 2+ + K + + Na + CEC rff ________________________ X 100 6868 =75%= %BS OAc = Ca 2+ + Mg 2+ + K + + Na + CEC OAc ________________________ X 100 6 10 =60%=

47. Anion adsorption and retention on soils: Negatively-charged ions adsorbed on positively-charges sites. In general, anion adsorption is associated with allophane and the hydrous oxides of Fe and Al in soils.In general, anion adsorption is associated with allophane and the hydrous oxides of Fe and Al in soils. H 2 PO 4 - >> SO 4 -2- >> NO 3 - > Cl - (the latter being nil in all but the most sequoixide-rich soils)H 2 PO 4 - >> SO 4 -2- >> NO 3 - > Cl - (the latter being nil in all but the most sequoixide-rich soils) Anion adsorption on these surfaces is highly dependent upon pH.Anion adsorption on these surfaces is highly dependent upon pH. Usually much lower than CEC in temperate, non- volcanic ash soils.Usually much lower than CEC in temperate, non- volcanic ash soils.

48. Al OH + 2 Cl - Low pH (protonated, anion exchange site) Al OH Al O - OH K + Zero Point of ChargeHigh pH (depronotated, cation exchange site) Allophane, Fe and Al hydrous oxides are amphoteric: they take on different charges depending upon pH:

49. Soil pH pH is the negative log of the H + activity = -log (H + ); therefore,pH is the negative log of the H + activity = -log (H + ); therefore, 10 -pH = (H + ) (in moles L -1 )10 -pH = (H + ) (in moles L -1 ) Soil reaction, or pH is taken in a paste of water or 0.01 CaCl 2.Soil reaction, or pH is taken in a paste of water or 0.01 CaCl 2. The latter gives a lower pH than the former, in most cases, because the Ca 2+ displaces exchangeable H + and Al 3+ by mass action.The latter gives a lower pH than the former, in most cases, because the Ca 2+ displaces exchangeable H + and Al 3+ by mass action.

50. Soil pH pH decreases as base saturation decreases (recall that you must keep the methods constant, that is by sum, eff, or Oac; the soil in Figure 4 has only one pH although base saturation value differs by method).pH decreases as base saturation decreases (recall that you must keep the methods constant, that is by sum, eff, or Oac; the soil in Figure 4 has only one pH although base saturation value differs by method). pH has a strong effect on plant growth and nutrient availability It not only changes the solubility of many nutrients, but may also cause direct toxicity (Al, usually) to plant roots.pH has a strong effect on plant growth and nutrient availability It not only changes the solubility of many nutrients, but may also cause direct toxicity (Al, usually) to plant roots.

51. http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_soil_reaction_ph.html

52. Buffering capacity: Ability of the soil to resist changes in pH.Ability of the soil to resist changes in pH. Related to exchangeable H + and Al 3+ in acid soils and carbonates in alkaline soils. Related to exchangeable H + and Al 3+ in acid soils and carbonates in alkaline soils. CEC always plays a major role in buffering.CEC always plays a major role in buffering. Total acidity on solid phase > 10,000 x that in soil solution Potential Acidity Active Acidity Buffering

53. Basic Soil Biological Properties Difficult to generalize what is a “good” soil relative to microorganisms C:N Ratio: major factor affecting decomposition and N availabilityC:N Ratio: major factor affecting decomposition and N availability pH: low pH disfavors bacteria and favors fungipH: low pH disfavors bacteria and favors fungi Aeration/flooding: anaerobes vs aerobesAeration/flooding: anaerobes vs aerobes

54. Soil Micro-organisms Many ways to classify Based on how they get energy:Based on how they get energy: Autotrophic: Use sunlight of inorganic chemical reactions for energyAutotrophic: Use sunlight of inorganic chemical reactions for energy Heterotrophic: Use organic compounds for energyHeterotrophic: Use organic compounds for energy Based on oxygen requirements:Based on oxygen requirements: AerobicAerobic AnaerobicAnaerobic FacultativeFacultative

55. Some Important Heterotrophs FungiFungi Decomposers (tolerate low pH)Decomposers (tolerate low pH) Mycorrhizae (vital for growth of many plants)Mycorrhizae (vital for growth of many plants) Bacteria/ActinomycetesBacteria/Actinomycetes Decomposers (do not tolerate low pH)Decomposers (do not tolerate low pH) Denitrifying bacteria (anaerobic)Denitrifying bacteria (anaerobic) Sulfur reducing bacteria (anaerobic)Sulfur reducing bacteria (anaerobic) Nitrogen fixersNitrogen fixers Rhizobium: legumesRhizobium: legumes Frankia actinomycetes: alders, snowbrush…Frankia actinomycetes: alders, snowbrush…

56. Decomposition and N-Mineralization and Immobilization in Soils: Critical Processes for Plant Nutrition!!! Most N taken up by plants in forest ecosystems is derived from decomposed organic matter (recycled)Most N taken up by plants in forest ecosystems is derived from decomposed organic matter (recycled) Decomposition is microbially mediated, yet microbial biomass is < 3% of soil OMDecomposition is microbially mediated, yet microbial biomass is < 3% of soil OM Microbes have higher concentrations of nutrients than the substrates they consumeMicrobes have higher concentrations of nutrients than the substrates they consume For example, bacteria and fungi have C:N ratios of around 6 to 1 (4 to 8% N), whereas substrates they consume have C:N ratios of 25 to 200 (3.0 to 0.05% N)For example, bacteria and fungi have C:N ratios of around 6 to 1 (4 to 8% N), whereas substrates they consume have C:N ratios of 25 to 200 (3.0 to 0.05% N)

57. Nitrogen Cycling in Soil:  Microbes concentrate nutrients in their bodies  This is termed immobilization Organic Substrate C:N = 200 Carbon Nitrogen CO 2 Microbes C:N = 12 Organic acids Immobilization

58. Nitrogen Cycling in Soil:  When microbes concentrate nutrients in their bodies  This is termed immobilization  When microbes release N from during decomposition  This is termed mineralization Organic Substrate C:N = 200 Carbon Nitrogen CO 2 Microbes C:N = 12 Immobilization Mineralization

59. Material C/N ratio Soil Microbes Bacteria 6:1 Actinomycetes 6:1 Fungi 12:1 Litter Types Alfalfa 13:1 Clover 20:1 Straw 80:1 Deciduous litter 40:1 to 80:1 Coniferous litter 60:1 to 130:1 Woody litter 250:1 to 600:1 Soil Organic Matter 10:1 to 50:1 Nitrogen Cycling in Soils: Importance of the C:N Ratio

60. C:N Ratio In order for soil microbes to decompose most litter types, they must initially incorporate N from the soilIn order for soil microbes to decompose most litter types, they must initially incorporate N from the soil Thus, inputs of high C/N ratio organic matter, such as sawdust or wood chips, can cause N deficiency to plants unless accompanied by fertilizationThus, inputs of high C/N ratio organic matter, such as sawdust or wood chips, can cause N deficiency to plants unless accompanied by fertilization As C is lost at CO 2 gas, the C/N ratio of the litter decreases to a value ranging from 20:1 to 30:1, at which point N is released from decomposing litterAs C is lost at CO 2 gas, the C/N ratio of the litter decreases to a value ranging from 20:1 to 30:1, at which point N is released from decomposing litter

61. Nitrogen Cycling in Soil:  Microbes concentrate nitrogen in their bodies  This is termed immobilization  When microbes release N from during decomposition  This is termed mineralization Organic Substrate C:N = 200 Carbon Nitrogen CO 2 Microbes C:N = 12 Organic acids Immobilization NH 4 +

62.  During decomposition, C:N ratio declines as C is lost to CO 2  When C:N ratio reaches about 20, N mineralization commences  Before that, N is immobilized C:N 600 20 N immobilization N mineralization Time of decomposition Sawdust Aspen leaves Clover NH 4 +

63. Other Important heterotrophs Mycorrhizae: Essential for nutrient and water uptake in most plants Denitrifying bacteria: N loss to gas in anaerobic conditions Nitrogen fixers: Convert N 2 gas in the atmosphere to ammonium (NH 4 + )Convert N 2 gas in the atmosphere to ammonium (NH 4 + ) Very important source of N for soils and vegetation, especially in unpolluted areas – soils have no mineral N source!Very important source of N for soils and vegetation, especially in unpolluted areas – soils have no mineral N source! The atmosphere is 78% N 2 gas but plants cannot utilize it because of the strong triple bond:The atmosphere is 78% N 2 gas but plants cannot utilize it because of the strong triple bond: N=N N=N Nitrogen fixers take energy from host plants (symbiotic) or associate (non-symbiotic) and convert this N to usable form using nitrogenase enzymeNitrogen fixers take energy from host plants (symbiotic) or associate (non-symbiotic) and convert this N to usable form using nitrogenase enzyme

64. Some Important Chemautotrophs Nitrifying bacteria One of the most important autorophic bacteria are nitrifying bacteria, who convert ammonium (NH 4 + ) to nitrite (NO 2 - ) and nitrate (NO 3 - ): 2NH 4 + + 3O 2  2NO 2 - + 4H + + 2H 2 ONitrosomonas 2NO 2 - + O 2 _  2NO 3 - Nitrobacter 2NH 4 + + 4O 2  4H + + 2H 2 O 2NO 3 - Note that nitrification is acidifying, and therefore self-limiting (in theory) because bacteria do now tolerate low pH. However, nitrification has been observed many times in very acid soils.

65. Sulfur oxidizing bacteria Another important chemautotroph is Genus Thiobacillus; most important of chemautotroph mineral oxidizers (elemental sulfur and sulfide minerals). For elemental S: 2S + 3O 2 + 2H 2 O -------> 4H + + 2SO 4 2- Thiobacillus thiooxidans Some Important Chemautotrophs Another important reaction carried out by these bacteria is the oxidation of pyrite, FeS 2, which occurs commonly in mine spoils by Thiobacillus thiooxidans and Thiobaccillus ferroxidans: 4FeS 2 + 150 2 + 2H 2 O  2Fe 2 (SO 4 ) 3 + 4H + + 2SO 4 2- Both reactions produce strong acid

66. So given that brief background, what is a “good” quality soil? I am guessing: Relatively rich in organic matterRelatively rich in organic matter Good N status (meaning: low C:N ratio)Good N status (meaning: low C:N ratio) Circumneutral pHCircumneutral pH Good supplies of P, K, Ca, Mg, S and micronutrientsGood supplies of P, K, Ca, Mg, S and micronutrients Good texture or structure (water holding capacity)Good texture or structure (water holding capacity) Bulk density near 1.0 (good infiltration and aeration, not compacted)Bulk density near 1.0 (good infiltration and aeration, not compacted) But what does all this imply for: Plants with varying nutritional needsPlants with varying nutritional needs Invasive speciesInvasive species Water qualityWater quality Soil water characteristicsSoil water characteristics?

67. Case Study 1: Compaction Bob Powers LTSP sites included experimental compactionBob Powers LTSP sites included experimental compaction Gomez et al (2002)* reported some resultsGomez et al (2002)* reported some results Many thanks to Bob for providing the following slides for my class!Many thanks to Bob for providing the following slides for my class! *Gomez, A., R.F. Powers, M.J. Singer, and W.R. Horwath. 2002. Soil compaction effects on growth of young ponderosa pine following litter removal in California’s Sierra Nevada. Soil S ci. Soc. Amer. J. 66: 1334-1343.

71. SEVERE COMPACTION BULK DENSITY SOIL BULK DENSITY (Mg m 2 at10-20 cm) BULK DENSITY BEFORE COMPACTION

72. SANDY LOAM 0.00 0.10 0.20 0.30 0.40 0.50 0.60 No CompactionSevere Compaction TREATMENT PORE VOLUME (cm 3 cm -3 >30  m 30-0.2  m <0.2  m ) Soil Pore Diam. INFLUENCE OF COMPACTION ON SOIL PORES BY FUNCTIONAL GROUPINGS

73. Soil Texture Total Soil Porosity (cm 3 /cm 3 ) Total Porosity Decrease (cm 3 /cm 3 ) Non- Compacted Treatments Compacted Treatments AbsRel % Loam 0.640.600.046 Sandy loam 0.550.510.047 Clay loam 0.550.560.012 Loam (volcanic ash) 0.630.620.012 Measured Total Soil Porosity

74. Decrease in Soil Pores >30µm as a Result of Soil Compaction Soil Texture Soil Macro Pores (cm 3 /cm 3 ) Decrease in Soil Macro Pores Non- Compacted Treatments Compacted Treatments AbsRel % Loam 0.290.180.1138 Sandy loam 0.290.190.1034 Clay loam 0.230.180.0522 Loam (volcanic ash) 0.290.220.0724

75. WHAT DOES COMPACTION DO TO SITE PRODUCTIVITY? Clay 0 20 40 60 80 100 12 Trees TOTAL BIOMASS (Mg ha - 1 ) No Compaction Severe Compaction PRODUCTIVITY SEVERELY REDUCED ON CLAY TEXTURES Understory

76. PRODUCTIVITY SLIGHTLY REDUCED ON ASH AND LOAM TEXTURES WHAT DOES COMPACTION DO TO SITE PRODUCTIVITY?

77. PRODUCTIVITY INCREASED ON SANDY TEXTURES WHAT DOES COMPACTION DO TO SITE PRODUCTIVITY?

78. CLAYEY 0.0 1.5 2.0 1.0 0.5 RELATIVE BIOMASS SOIL TEXTURAL CLASS 4 LOAMY 16 SANDY 6 Uncompacted Control EFFECT OF SEVERE SOIL COMPACTION ON PRODUCTIVITY VARIES BY SOIL TEXTURE (26 LTSP INSTALLATIONS)

79. Gomez, A., R.F. Powers, M.J. Singer, and W.R. Horwath. 2002. Soil compaction effects on growth of young ponderosa pine following litter removal in California’s Sierra Nevada. Soil S ci. Soc. Amer. J. 66: 1334-1343.

80. Lesson from Case Study 1: Compaction can either increase or decrease soil quality as defined by: Soil water characteristicsSoil water characteristics Tree growthTree growth

81. So given that brief background, what is a “good” quality soil? Good N status (low C:N ratio) and circumneutral pH is fertile ground for nitrifying bacteria. What does this imply for nitrate pollution of ground and surface waters? What does good N status imply for N-loving invasive species like cheatgrass? What does it imply for native N-fixers like alder and snowbrush? What does circumneutral pH imply for the competitive advantage of native acid-tolerant species on naturally acidic soils?

82. Case Study 2 Here are some soil data from two forested ecosystems with different vegetation cover for the last 50 years. Which soil is of better quality? Depth (cm) SoilpH%BSC (mg g -1 ) N C:N Bray P (mg kg -1 ) Db (g cm -3 ) 0-1515.3±0.213±743±111.6±0.42782±390.96±0.11 0-1524.5±0.28±595±264.8±1.52921±140.85±0.18 15-3015.3±0.212±829±101.2±0.32443±291.03±0.12 15-3024.8±0.27±459±173.2±0.71810±60.86±0.15 30-4515.3±0.19±526±81.2±0.22230±191.13±0.13 30-4524.9±0.29±858±243.1±1.1198±31.01±0.21

83. DepthpH%BS C (mg g -1 ) N (mg g -1 ) cm Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 0-155.3±0.24.5±0.213±78±543±1195±261.6±0.44.8±1.5 15-305.3±0.24.8±0.212±87±429±1059±171.2±0.33.2±0.7 30-455.3±0.14.9±0.29±59±826±858±241.2±0.23.1±1.1 DepthC:N Bray P (mg kg -1 ) Db (g cm -3 ) cm Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 0-15272982±3921±140.96±0.110.85±0.18 15-30241843±2910±61.03±0.120.86±0.15 30-45221930±198±31.13±0.131.01±0.21 Case Study 2 Here are some soil data from two forested ecosystems with different vegetation cover for the last 50 years. Which soil is of better quality?

84. Case Study 2 Soil 1 is from a Douglas-fir stand, soil 2 is from an adjacent red alder stand. Same soils before vegetation changed (Van Miegroet and Cole, 1984). So how do these soil properties affect tree growth? DepthpH%BS C (mg g -1 ) N (mg g -1 ) cm Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 0-155.3±0.24.5±0.213±78±543±1195±261.6±0.44.8±1.5 15-305.3±0.24.8±0.212±87±429±1059±171.2±0.33.2±0.7 30-455.3±0.14.9±0.29±59±826±858±241.2±0.23.1±1.1 DepthC:N Bray P (mg kg -1 ) Db (g cm -3 ) cm Soil 1 Soil 2 Soil 1 Soil 2 Soil 1 Soil 2 0-15272982±3921±140.96±0.110.85±0.18 15-30241843±2910±61.03±0.120.86±0.15 30-45221930±198±31.13±0.131.01±0.21

86. Van Miegroet et al., 1989 Planting red alder on former red alder soil resulted in slower growth than planting red alder on former Douglas-fir soil.Planting red alder on former red alder soil resulted in slower growth than planting red alder on former Douglas-fir soil. At this stage, no response in Douglas-fir, but past experience has shown that it will grow much better on former red alder soil.At this stage, no response in Douglas-fir, but past experience has shown that it will grow much better on former red alder soil. (The stand was destroyed in a wind storm after these measurements were taken).(The stand was destroyed in a wind storm after these measurements were taken).

87. Interplantings of red alder and conifers (Binkley, 2003) Initially, red alder inhibits D. fir growth in the poorer (Wind River) siteInitially, red alder inhibits D. fir growth in the poorer (Wind River) site Over time, D. fir takes the site, grows faster because of more N in soil at Wind RiverOver time, D. fir takes the site, grows faster because of more N in soil at Wind River At N-rich Cascade Head site, alder continues to inhibit D. FirAt N-rich Cascade Head site, alder continues to inhibit D. Fir

88. Van Miegroet et al., 1984 What about water quality considerations? The red alder soil produced high rates of nitrate leaching and no doubt contributed to soil acidification

89. What about water quality considerations? Subsequent studies by Compton et al (2003) showed that nitrate in streamwater from Oregon Coast Watersheds was related to the presence of red alder.

90. What about water quality considerations? Harvesting in red alder caused large reductions in nitrate leaching Water quality problems were related to excessive N-fixation, not directly to soil properties in this case

91. Summary of Case Study 2 Red alder improves C and N status of soils, which is good for Douglas-fir. But this comes at a price in water quality.Red alder improves C and N status of soils, which is good for Douglas-fir. But this comes at a price in water quality. Red alder acidifies soils which is (apparently) not good for red alder but does not bother Douglas-firRed alder acidifies soils which is (apparently) not good for red alder but does not bother Douglas-fir Therefore, what is good soil quality for Douglas-fir is not good quality for red alder.Therefore, what is good soil quality for Douglas-fir is not good quality for red alder.

92. Case Study 3, Site 1 Here are some soil data from adjacent sites which have had different vegetation cover for 100 years. Which soil is of better quality? Vegetation 1 Vegetation 2

93. Case Study 3, Site 1 (cont) Vegetation 1 Vegetation 2 Soil data from adjacent sites which have had different vegetation cover for 100 years.

94. Veg 1 Veg 2 Case Study 3, Site 2 Here are some soil data from adjacent sites which have had the same two vegetation covers but for only two decades. Which soil is of better quality? Vegetation 1 Bulk Density (g cm -3 ) Vegetation 2 Veg 1 Veg 2 Veg 1 Veg 2Depthcm Soil 1 Soil 2 0-71.34±0.041.15±0.04 7-201.43±0.051.29±0.03 20-401.42±0.051.32±0.02

95. Veg 2: Pinus jeffreyii Comparisons of soils in beneath 5 paired adjacent, mature stands of Ceanothus velutinus and Pinus jeffreyii in Little Valley, Nevada (Johnson, 1995). Veg 1: Ceanothus velutinus Site 1: Upper Little Valley, Nevada. Mature, adjacent snowbrush and 100 year old jeffrey pine stands.

96. Immediate post-fire Foliage and forest floor are totally combustedFoliage and forest floor are totally combusted Soil organic matter losses unknownSoil organic matter losses unknown 20 years post-fire 80% N-fixing Ceanothus velutinus80% N-fixing Ceanothus velutinus 20% non-fixing shrubs20% non-fixing shrubs Site 2: In and near 1981 wildfire in lower Little Valley, Nevada. 20-year- old snowbrush and nearby mature jeffrey pine stands.

97. Soil solutions from beneath snowbrush in upper Little Valley had extremely low (< 3 umol c L -1 ) nitrate concentrations (Johnson, 1995)

98. Soil solutions from snowbrush-dominated former fire site in Little Valley had only slightly elevated nitrate concentrations (Stein, 2006)

99. Both studies showed that snowbrush improves soil quality.Both studies showed that snowbrush improves soil quality. Furthermore, soil solution data from both sites showed that snowbrush, unlike red alder, produce only very slight increases in nitrate leaching and does not acidify soils, but in fact, increases base saturation.Furthermore, soil solution data from both sites showed that snowbrush, unlike red alder, produce only very slight increases in nitrate leaching and does not acidify soils, but in fact, increases base saturation. So why not manage for snowbrush if we want to improve soil quality?So why not manage for snowbrush if we want to improve soil quality? Because snowbrush competes with regenerating forest vegetation for water; if measures are not taken to control it, former forests will revert to chaparral for 50- 100 years after wildfire!Because snowbrush competes with regenerating forest vegetation for water; if measures are not taken to control it, former forests will revert to chaparral for 50- 100 years after wildfire! Summary of Case Study 3 Snowbrush studies in Little Valley

100. Nitrogen has some features that are unique among major nutrient that make it most frequently limiting and problematic: No significant primary mineral sourceNo significant primary mineral source Will not accumulate in ionic form in soils in any substantial amounts for longWill not accumulate in ionic form in soils in any substantial amounts for long N present in excess of biological demand nearly always nitrifies (if not already in NO 3 - form) and leaches away as NO 3 -, causing water pollution and soil acidificationN present in excess of biological demand nearly always nitrifies (if not already in NO 3 - form) and leaches away as NO 3 -, causing water pollution and soil acidification The Nitrogen Problem

101. Nitrogen has a very narrow “sufficiency or optimum plateau” after which bad things start to happen and before which N is deficient (soil quality is low) The Nitrogen Problem Deficiency Toxicity Sufficiency Growth-limiting Enough but, possibly more Then enough, but not too much Too much – growth inhibited, negative effects on soil and water Nitrogen P, K, Ca, Mg, S

102. Nitrogen is the most frequently limiting nutrient and a high quality soil must have adequate N. However, it is very difficult to manage nitrogen at an optimal level for plant growth while at the same time maintaining water quality and not causing negative effects on other soil nutrients (and causing deteriorating soil quality) The Nitrogen Problem

103. A single soil quality standard does not make any sense: Plants vary in nutritional needsPlants vary in nutritional needs Invasive species tend to love high quality soilInvasive species tend to love high quality soil We tend to like like oligotrophic (nutrient poor) surface waterWe tend to like like oligotrophic (nutrient poor) surface water Soil quality, or soil fertility as it was previously termed, should be viewed from the perspective of management objectives and priorities: Increase productionIncrease production Grow specific species (some love acid, some cannot tolerate it)Grow specific species (some love acid, some cannot tolerate it) Control invasive speciesControl invasive species Preserve water qualityPreserve water quality Summary and Conclusions It is probable that not all of these objectives can be met at once with the same soil quality standard!