Leaving at 8:30 am Be prepared for a little mud!

Transcription

1 Field Trip Overview Day trip to Tyson Research Center on Saturday Leaving at 8:30 am from bus drop by Mallinckrodt Center Don t be late!!! You cannot enter the site if you drive there on your own Forecast: Partly cloudy, mid-40s in morning, upper-50s by afternoon Wear layers; Be prepared for a little mud! Bring a notebook and pen or pencil; A camera would also be helpful, as would be bug spray and sunscreen Bring a lunch, snacks, and water Prof. Catalano will provide bagels and coffee, but there is no other food available on the field trip Our goal is to return by 4:30 pm, hopefully earlier

2 Lecture 23: Salt-Affected Soils; Introduction to Soil Mapping

3 Measures of Soil Salinity and Classification of Salt-Affected Soils

4 Measures of Total Soil Salinity Electrical Conductivity (EC): Conductivity is generally proportional to salinity Multiple EC methods used EC of a solution extracted from a water-saturated soil paste is the most common method used New probes measure EC directly in the field Total Dissolved Solids (TDS): Mass of dissolved salts per unit volume of soil water or the solution extracted from a water-saturated soil paste EC-TDS relationship varies with the type of salt present

5 Measures of Sodium Status Not a measure of concentration!!!! Exchangeable sodium percentage (ESP) + Exchangeable Na, cmolc / kg ESP = 100 CEC, cmolc / kg Exact same parameter as sodium saturation ESP > 15% is associated with degraded soils and high ph Sodium adsorption ratio (SAR) SAR = [ Na ] ([ Ca ] + [ Mg ]) Concentrations of ions in the soil solution in mmol c /L SAR is easier to measure than ESP SAR = 13 is approximately equal to ESP = 15

6 Classes of Salt-Affected Soils Saline: High salt, low sodium, ph often <8.5 Saline-Sodic: High salt, high sodium, ph often <8.5 Sodic: Low salt, high sodium, ph often >8.5 May form by leaching saline-sodic soils

7 Key Concepts in the Classification of Salt-Affected Soils Sodium status is a measure of the percentage of exchangeable cations that are sodium Measured as ESP or SAR This is a relative measure; it does not requires soils to have a lot of salt Salt-affect soils are classified by the amount of salt present (salinity, measured by electrical conductivity) and the sodium status Familiarize yourself with this classification

8 Sodic Soils

9 General Features of Sodic Soils Natric subsurface horizons may be present ph is high because no further CaCO 3 precipitation can occur; all Ca is used up Evaporation can raise ph to 10.5 Many plants do not tolerate high sodium and high ph Sodic soils often have poor structure High ph may disperse organic matter High Na + causes soil minerals to disperse

10 Sodic Soil with a Natric Horizon

11 Physical Degradation of Soil by Sodic Conditions Exchangeable sodium increases slaking, the breakup of aggregates when wet The silt and clay released then clog soil pores Na + -saturated 2:1 clays swell more than if the interlayer contains other cations, closing pores Most important: High sodium and low salt cause dispersion of soil particles Opposite of flocculation, which helps form soil aggregates Destroys aggregates, macropores, and most soil structure These processes can also occurs in non-arid soils from addition of sodium (e.g., road salt)

12 Cation Controls on Soil Dispersion High salt concentrations and strongly attracted ions (e.g., calcium) promote flocculation, aggregation, and high permeability Low salt concentrations and weakly attracted ions (e.g., sodium) encourage dispersion, puddling, and low permeability

13 Sodium and Low Salinity Causes Dispersion, Degrading Soil Structure Alkaline, Low SAR/ESP Low Salinity High Salinity Alkaline, High SAR/ESP Dispersion

14 Soil Dispersion in Water Increasing ESP/SAR (More Exchangeable Sodium, Less Exchangeable Calcium) High sodium and low total salt content (low EC) causes soil aggregates to degrade, with the soil particles dispersing into water Images from:

15 Example of a Clay-Rich Soil with High Dispersion from Sodium

16 High Exchangeable Sodium Reduces Hydraulic Conductivity of Soil Sodic soil often have poor infiltration and high runoff, further reducing available water in already arid soils

17 Dispersive Soils are Prone to Waterlogging and Erosion Images from:

18 Key Concepts in Sodic Soils Have high ph because no Ca present to buffer the system May have natric horizons (if subsurface clay accumulation is present) Sodic soils are poorly vegetated and often have poor structure Soil minerals and OM are dispersed by Na +, may see loss of soil structure (puddling) The addition of sodium to a soil causes physical degradation

19 Soil Surveys and Soil Mapping Soil Profile Descriptions

20 Field Mapping Methods: Soil Profile Descriptions When mapping it is essential to examine soil profiles in the area For each soil profile: Identify the horizons Determine diagnostic features Assign to a soil series

21 Profile Description for the Thorndale Soil Series, a Fine-silty, mixed, active, mesic Typic Fragiaqualf

22 Group Activity: Determine the Soil Series! Break up into four groups Read the soil series description Prof. Catalano has conveniently removed the overview paragraph and taxonomic class Discuss among your group members the likely soil order for each series and the reasons why you made this assignment Nominate someone to present and justify your soil order assignments to the class

23 Rusty Series The Rusty series consists of very deep, well drained soils that formed in lacustrine sediments reworked by wind. The sediments are from mixed rock sources. These soils are on lake plains and have slopes of 0 to 8 percent. The mean annual precipitation is about 125 mm and the mean annual temperature is about 12 degrees C. TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Typic Natrargids

24 Swanlake Series The Swanlake series consists of very deep, well drained soils that formed in loamy calcareous till on ground moraines and till plains. Slope ranges from 2 to 6 percent. Mean annual air temperature is about 9 degrees C (48 degrees F). Mean annual precipitation is about 711 mm (28 inches). TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Typic Calciudolls

25 Skerry Series The Skerry series consists of very deep, moderately well drained soils that formed in a loamy mantle overlying dense, sandy till on drumlins and glaciated uplands. They are moderately deep to a densic contact. Saturated hydraulic conductivity is moderately high or high in the mineral solum and moderately low or moderately high in the dense substratum. Slope ranges from 0 through 25 percent. Mean annual precipitation is about 40 inches, and mean annual temperature is about 43 degrees F. TAXONOMIC CLASS: Coarse-loamy, isotic, frigid Aquic Haplorthods

26 Possumtrot Series The Possumtrot series consists of very deep, well drained soils on low stream terraces and flood plains. These soils formed in loamy stream alluvium. Permeability is moderately rapid. Slopes range from 0 to 3 percent. Mean annual temperature is 56 degrees F., and the mean annual precipitation is about 42 inches. TAXONOMIC CLASS: Coarse-loamy, siliceous, superactive, mesic Fluventic Dystrudepts