Soil Quality Indicators: Physical Properties

Measuring Available Water Capacity

-AWC (mm) = [drained upper limit (amount of water soil holds after drainage has stopped) - crop lower limit (extent to which a certain crop can extract water from a particular soil] x [depth interval (cm)/10] <--- per profile -total profile = sum of AWC per profile

Measuring SS + MP

-ribbon test -settling

Improving Bulk Density

-Any practice that improves soil structure decreases bulk density -tillage at the beginning of the growing season temporarily decreases bulk density and disturbs compacted soil layers, but subsequent trips across the field by farm equipment, rainfall events, animals, and other disturbance activities can recompact soil -long-term solutions to bulk density and soil compaction problems revolve around decreasing soil disturbance and increasing soil organic matter. A system that uses cover crops, crop residues, perennial sod, and/or reduced tillage results in increased soil organic matter, less disturbance and reduced bulk density -the use of multi-crop systems involving plants with different rooting depths can help break up compacted soil layers. • Minimize soil disturbance and production activities when soils are wet, • Use designated field roads or rows for equipment traffic, • Reduce the number of trips across the area, • Subsoil to disrupt existing compacted layers, and • Use practices that maintain or increase soil organic matter. -Grazing systems that minimize livestock traffic and loafing, provide protected heavy use areas, and adhere to recommended minimum grazing heights reduce bulk density by preventing compaction and providing soil cover • Conservation Crop Rotation • Cover Crop • Deep Tillage • Prescribed Grazing • Residue and Tillage Management

Improving aggregate stability

-Any practice that increases soil organic matter, and consequently biological activity, improves aggregate stability -slow to recover -Aggregates form readily in soil receiving organic amendments, such as manure. They also form readily where cover and green manure crops and pasture and forage crops are grown, and where residue management and/or reduced tillage methods are used. -cover and green manure crops, residue management, sod-based rotations, and decreased tillage and soil disturbance. • Conservation Crop Rotation • Cover Crop • Pest Management • Prescribed Grazing • Residue and Tillage Management • Salinity and Sodic Soil Management • Surface Roughening

Dynamic Factors Affecting Bulk Density

-Bulk density is changed by crop and land management practices that affect soil cover, organic matter, soil structure, and/or porosity -Plant and residue cover protects soil from the harmful effects of raindrops and soil erosion. Cultivation destroys soil organic matter and weakens the natural stability of soil aggregates making them susceptible to damage caused by water and wind. When eroded soil particles fill pore space, porosity is reduced and bulk density increases -Livestock and agricultural and construction equipment exert pressure that compacts the soil and reduces porosity, especially on wet soils.

Inherent Factors Affecting SS + MP

-Clay particles carry a negative charge on their surface that can cause them to repel each other, but that attracts and adsorbs cations present in the soil. Stacks of clay particles can form when their negative surface charge is neutralized by tightly adsorbed polyvalent cations, such as Ca2+ and Al3+. Further, Ca2+, Fe2+ and Al3+ flocculate (clump together) stacks of clay particles, and with humus (negatively charged, highly decomposed, stable organic matter), bind to form small, stable soil aggregates. -In contrast, sodium ions (Na+) are associated with soil dispersion. They are monovalent, relatively large and they are the prominent cation adsorbed to clay particles in some soils in arid and semi-arid regions. Because of their relatively weak charge and large size, sodium ions are ineffective at promoting clay stacking and aggregate formation. Dispersed clay causes the soil to be almost structureless, impervious to water and air, and undesirable for plant growth. -When soil dries out and water is removed, clay stacks move closer together, the soil shrinks in volume, and cracks develop in weakly bonded areas. As soil wetting and drying cycles are repeated with rainfall (or irrigation) and removal by plants, an extensive network of cracks develops and soil aggregates become more defined. Freezing and thawing cycles have a similar shrinking and swelling effect since freezing of soil water to form ice crystals withdraws water from clay structures. Shrinking and swelling breaks apart and compresses soil particles into defined structural aggregates. Certain types of clay particles have shrink-swell properties of their own.

Measuring Aggregate Stability

-Determine for the top three inches of soil. However, in rangeland conditions determine for the top ¼ to ½ inch of soil as it is most likely to be removed by erosion. A 400- watt hairdryer and drying chamber are required to conduct the wet aggregate stability test. -exposure to energy and seiving

Improving Available Water Capacity

-Farmers can grow high residue crops, perennial sod and cover crops, reduce soil disturbing activities, and manage residue to protect and increase soil organic matter to make improvements in a soil's available water capacity -tillage, harvest, and other farming operations requiring heavy equipment can be avoided when the soil is wet to minimize compaction; and compacted layers can be ripped to break them and expand the depth of the soil available for root growth -irrigation to leach salts below the root zone and practices that promote infiltration, reduce evaporation, minimize disturbance, manage residue, and prevent mixing of salt-laden lower soil layers with surface layers • Conservation Crop Rotation • Cover Crop • Prescribed Grazing • Residue and Tillage Management • Salinity and Sodic Soil Management

Problems with Poor Bulk Density

-High bulk density is an indicator of low soil porosity and soil compaction. It may cause restrictions to root growth, and poor movement of air and water through the soil -Compaction can result in shallow plant rooting and poor plant growth, influencing crop yield and reducing vegetative cover available to protect soil from erosion. -By reducing water infiltration into the soil, compaction can lead to increased runoff and erosion from sloping land or waterlogged soils in flatter areas • Consistently plowing or disking to the same depth, • Allowing equipment traffic, especially on wet soil, • Using a limited crop rotation without variability in root structure or rooting depth, • Incorporating, burning, or removing crop residues, • Overgrazing forage plants, and allowing development of livestock loafing areas and trails, and • Using heavy equipment for building site preparation or land smoothing and leveling.

Problems with Poor Available Water Capacity

-Lack of available water reduces root and plant growth, and it can lead to plant death if sufficient moisture is not provided before a plant permanently wilts. A soil's ability to function for water storage also influences runoff and nutrient leaching. -practices that prevent accumulation of soil organic matter and/or result in soil compaction and reduced pore volume and size: • Conventional tillage operations, • Low residue crop rotations, and burning, burying, harvesting, or otherwise removing plant residues, • Heavy equipment traffic on wet soils, and • Grazing systems that allow development of livestock loafing areas and livestock trails. -As natural areas are permanently converted to homes, roads, and parking areas, the overall amount of water that can be stored in the soil is reduced. This leads to higher total runoff, increased pressure on storm water drainage systems, a higher likelihood of flooding, and generally poorer water quality in streams and lakes

Dynamic Factors Affecting Soil Crusts

-Management activities that deplete soil organic matter and leave soil bare, smooth and exposed to the direct impact of water droplets increase soil dispersion, surface sealing, runoff, erosion, and crusting -excessive tillage -Harvest methods that remove most or all of aboveground biomass also prevent or reduce organic matter buildup and protection of the soil surface -exposure to sunlight dries it up

Avoid Soil Crusting!

-No-till or reduced tillage of cropland is the best way to reduce or eliminate crust formation. If tillage is necessary, it should only be done to the minimum level required for good seed germination and emergence -Residue intercepts the force of falling raindrops and is a source of organic matter. Organic matter stabilizes soil aggregates making them more resistant to the physical impact of raindrops -Improved infiltration and water movement through soil decreases surface ponding and runoff, and helps protect soil from erosion. Good soil structure and aggregate stability are vital to supporting healthy, vigorous plants -To reduce the incidence of surface crusting of soils high in sodium, irrigation water management prevents sodium accumulation at the surface, and gypsum (calcium sulfate) can be applied to promote flocculation and inhibit dispersion of soil particle • Conservation Crop Rotation • Cover Crop • Residue and Tillage Management • Salinity and Sodic Soil Managemen

Problems with Slaking

-Slaked soil particles block soil pores, form a soil crust, reduce infiltration and water movement through soil, and increase runoff and erosion. Small aggregates produced by slaking settle together resulting in smaller pore spaces than where present with larger aggregates. Pore volume may be reduced and the ability of plants to use water stored in pore spaces may be altered. • Conventional tillage methods that disturb soil and accelerate organic matter decomposition, • Burning, harvesting or otherwise removing crop residues, and • Using pesticides harmful to soil organisms that cycle organic matter and promote aggregation. -to reduce slaking: • Conservation Crop Rotation • Cover Crops • Prescribed Grazing • Residue and Tillage management

Inherent Factors Affecting Slaking

-Slaking is affected by wetting rate, soil water content, soil texture, type of clay, and organic matter -Slaking is increased by fast wetting rates, particularly when soil is initially dry. Moist aggregates slake less readily than air-dry aggregates because they have already completed some or all of their swelling and some pores are already filled with water -The pressure of entrapped air is the primary factor for causing slaking of loamy soils, while clay is associated with slaking caused by soil swelling -Slaking is influenced by the presence of smectitic clays, such as montmorillonite, that shrink when dry and swell when wet. Soil water forms part of the structure of these clays. Montmorillonite can swell 25 times more than kaolinite. The presence of even small quantities of smectites in kaolinitic soils can dramatically affect slaking, soil dispersion and surface sealing. Soils with high shrinkswell potential are common in the central region of the United States -Fast wetting of high clay soil increases the extent of differential swelling and volume of entrapped air in pore space that create internal stress and break aggregates apart -Compared to the effects of raindrop splash on external breakdown of soil aggregates, slaking plays the primary role in particle detachment and surface sealing of clay soils with otherwise stable structure

Soil Structure and Macropores

-Soil structure is the combination or arrangement of primary soil particles into aggregates. Using aggregate size, shape and distinctness as the basis for classes, types and grades, respectively, soil structure describes the manner in which soil particles are aggregated. Soil structure affects water and air movement through soil, greatly influencing soil's ability to sustain life and perform other vital soil functions. -Macropores are large soil pores, usually between aggregates, that are generally greater than 0.08 mm in diameter. Macropores drain freely by gravity and allow easy movement of water and air. They provide habitat for soil organisms and plant roots can grow into them. With diameters less than 0.08 mm, micropores are small soil pores usually found within structural aggregates. Suction is required to remove water from micropores

Soil Crusts

-Structural soil crusts are relatively thin, dense, somewhat continuous layers of non-aggregated soil particles on the surface of tilled and exposed soils. Structural crusts develop when a sealed-over soil surface dries out after rainfall or irrigation. Water droplets striking soil aggregates and water flowing across soil breaks aggregates into individual soil particles. Fine soil particles wash, settle into and block surface pores causing the soil surface to seal over and preventing water from soaking into the soil. As the muddy soil surface dries out, it crusts over. -Soil crusting is also associated with biological and chemical factors. A biological crust is a living community of lichen, cyanobacteria, algae, and moss growing on the soil surface that bind the soil together. A precipitated, chemical crust can develop on soils with high salt content.

Inherent Factors Affecting Soil Crusts

-Surface crusts are more common on fine-textured soils, such as silts, loams and clays. In combination with the splashing effect of raindrops, increased runoff and erosion of fine-textured soil increases the likelihood that a crust will develop. Crusts are usually thin and weak if present on coarse textured, sandy soils. -Low organic matter results in poor soil structure, reduced pore space, and weak, unstable aggregates that fall apart when raindrops hit them -Soils with high sodium content are more likely to develop surface crusts since these soils are more readily dispersed with rainfall and irrigation.

Problems with Poor Infiltration

-When water is supplied at a rate that exceeds the soil's infiltration capacity, it moves downslope as runoff on sloping land or ponds on the surface of level land. When runoff occurs on bare or poorly vegetated soil, erosion takes place. Runoff carries nutrients, chemicals, and soil with it, resulting in decreased soil productivity, off-site sedimentation of water bodies and diminished water quality. Sedimentation decreases storage capacity of reservoirs and streams and can lead to flooding. -Restricted infiltration and ponding of water on the soil surface results in poor soil aeration, which leads to poor root function and plant growth, as well as reduced nutrient availability and cycling by soil organisms -. Ponding and soil saturation decreases soil strength, destroys soil structure, increases detachment of soil particles, and makes soil more erodible • Incorporating, burning, or harvesting crop residues leaving soil bare and susceptible to erosion, • Tillage methods and soil disturbance activities that disrupt surface connected pores and prevent accumulation of soil organic matter, and • Equipment and livestock traffic, especially on wet soils, that cause compaction and reduced porosity.

Dynamic Factors Affecting Available Water Capacity

-affected by organic matter, compaction, and salt concentration of the soil -Organic matter increases a soil's ability to hold water, both directly and indirectly. When a soil is at field capacity, organic matter has a higher water holding capacity than a similar volume of mineral soil -Indirectly, organic matter improves soil structure and aggregate stability, resulting in increased pore size and volume. These soil quality improvements result in increased infiltration, movement of water through the soil, and available water capacity -Compaction reduces available water capacity through its adverse affects on both field capacity and permanent wilting point. Compaction reduces total pore volume, consequently reducing water storage when the soil is at field capacity. Compaction also crushes large soil pores into much smaller micropores. Since micropores hold water more tightly than larger pores, more water is held in soil at its permanent wilting point -Salts in soil water result from fertilizer application or naturally occurring compounds. Salt concentration increases as soil water decreases. For soils high in soluble salts, moisture stress results when plants cannot uptakewater across an unfavorable salt concentration gradient. Soils with high salt concentration tend to have reduced available water capacity because more water is retained at the permanent wilting point than if water was held by physical factors alone. These effects are most pronounced in soils in dry regions where salts accumulate because of irrigation or natural processes

Inherent factors affecting aggregate stability

-amount and type of clay -absorbed cations like Ca and Na -iron and oxide content -expansion/contraction of clay particles when they become wet/dry shift and crack soil mass and create/break apart aggregates -Ca, Mg, Fe, and Al stabilize aggregates by forming organic matter -decreases w amount of Na: dispersion occurs when Na ions collect between soil particles

Dynamic Factors Affecting SS + MP

-biological processes are important for development of large aggregates and macropores, and they are the primary factor for aggregation of sandy soils. Important biological processes include: earthworms burrowing in soil and ingesting soil particles to form casts, development of sticky networks of roots and fungal hyphae, and production of organic glues by fungi and bacteria -Plant roots also contribute to aggregation and development of macropores as they push through the soil while they are growing or by leaving channels when they die. Mycorrhizae, or thread-like fungi, secrete a gooey protein called glomalin that is an effective cementing agent for providing short-term stability of large aggregates -Organic matter is the major contributing factor for aggregate formation that can be directly affected by human management. It provides energy for microbial processes that release organic products. The organic products chemically interact with soil particles and iron and aluminum oxides to bind soil particles together into aggregates. Tillage can have favorable and unfavorable effects on aggregation and soil structure. Short-term, tillage breaks clods apart, incorporates organic matter into the soil, and loosens it to increase porosity; however, longterm, tillage increases decomposition of organic matter, prevents accumulation, and reduces its aggregating effects. Tillage of wet soil generally destroys surface soil structure.

Inherent Factors Affecting Infiltration

-dependent on soil texture (percentage of sand, silt, and clay) and clay mineralogy -Water moves more quickly through the large pore spaces in a sandy soil than it does through the small pores of a clayey soil, especially if the clay is compacted and has little or no structure or aggregation -steady infiltration rate: sand >0.8 in/hr silt 0.2-0.4 in/hr clay 0.04-0.2 in/hr -many clayey soils develop shrinkage cracks as they dry, creating a direct conduit for water to enter the soil. These clay soils have high infiltration capacities as water moves into the shrinkage cracks, although at other times, when cracks are not present, their infiltration rate is characteristically slow

Inherent Factors Affecting Bulk Density

-dependent on soil texture and the densities of soil mineral (sand, silt, and clay) and organic matter particles, as well as their packing arrangement -most rocks have a bulk density of 2.65 g/cm3 so ideally, a medium textured soil with about 50 percent pore space will have a bulk density of 1.33 g/cm3 -loose, porous soils and those rich in organic matter have lower bulk density -Sandy soils have relatively high bulk density since total pore space in sands is less than that of silt or clay soils. Finer-textured soils, such as silt and clay loams, that have good structure have higher pore space and lower bulk density compared to sandy soils -Bulk density typically increases with soil depth since subsurface layers have reduced organic matter, aggregation, and root penetration compared to surface layers and therefore, contain less pore space. Subsurface layers are also subject to the compacting weight of the soil above them.

Dynamic Factors Affecting Infiltration

-existing soil water content affects the ability of the soil to pull additional water into it. Pores and cracks are generally open in a dry soil. Many of them are filled in by water or swelled shut as the soil becomes wet, so infiltration rate is generally highest when the soil is dry -Infiltration is affected by crop and land management practices that affect surface crusting, compaction, and soil organic matter. Without the protective benefits of vegetative or residue cover, bare soil is subjected to the direct impact and erosive forces of raindrops that dislodge soil particles. Dislodged soil particles fill in and block surface pores, contributing to the development of surface crusts that restrict water movement into the soil -Compaction results from livestock and equipment traffic, especially on wet soils, and continuous plowing to the same depth, e.g. the creation of a plow pan below the tillage depth. Compacted or impervious soil layers have reduced pore space and restricted water movement through the soil profile -Soil organic matter affects infiltration through its positive affect on the development of stable soil aggregates, or crumbs. Highly aggregated soil has increased pore space and infiltration. Soils high in organic matter also provide good habitat for soil biota, such as earthworms, that through their burrowing activities, increase pore space and create continuous pores linking surface to subsurface soil layers. -Management that reduces soil cover, disrupts continuous poor space, compacts soil, or reduces soil organic matter negatively impacts infiltration. Since tillage negatively affects all of these properties, it plays an important role in a soil's infiltration rate

Relationship of Available Water Capacity to Soil Function

-in areas where plants remove more water than is supplied by precipitation, the amount of water held by the soil may be critical -By holding water for future use, soil buffers the plant - root environment against periods of water deficit. -Available water capacity is used to develop water budgets, predict droughtiness, design and operate irrigation systems, design drainage systems, protect water resources, and predict yields

Improving Infiltration

-increasing vegetative cover, managing crop residues, and increasing soil organic matter -minimize soil disturbance and compaction, protect soil from erosion, and encourage the development of good soil structure and continuous pore space -Long-term solutions for maintaining or improving infiltration include practices that increase soil organic matter and aggregation, and reduce soil disturbance and compaction. High residue crops, such as corn and small grains, perennial sod, and cover crops protect the soil surface from erosion and increase soil organic matter when reduced tillage methods that maintain surface cover are used to plant the following crop -Application of animal manure also helps to increase soil organic matter. Increased organic matter results in increased aggregation and improved soil structure leading to improved infiltration rates • Conservation Crop Rotation • Cover Crop • Prescribed Grazing • Residue and Tillage Management • Waste Utilization

Relationship of soil aggregates to soil function

-indicator of organic matter content, biological activity, and nutrient cycling -smaller aggregates bound by older more stable forms of organic matter -material from microbial decomposition of organic matter is less stable and binds larger aggregates -larger particles better indicator of soil quality bc more susceptible to management effects on organic matter -stable aggregates = range in pore sizes

Bulk Density

-indicator of soil compaction -dry weight of soil/ volume -volume = volume of soil + volume of pores -g/cm^3

Available Water Capacity

-maximum amount of plant available water a soil can provide -indicator of a soil's ability to retain water and make it sufficiently available for plant use -Available water capacityis the water held in soil between its field capacity and permanent wilting point. Field capacity is the water remaining in a soil after it has been thoroughly saturated and allowed to drain freely, usually for one to two days. Permanent wilting point is the moisture content of a soil at which plants wilt and fail to recover when supplied with sufficient moisture -Water capacity is usually expressed as a volume fraction or percentage, or as a depth (in or cm).

Problems with Soil Crusts

-restrict seedling emergence, especially in non grass crops -reduce oxygen diffusion into the soil profile by as much as 50% if the soil crust is wet -reduces infiltration, increases erosion -The sunlight (and energy) reflectance of a surface crust is higher than that of a non-crusted soil, so soil temperature may be lower and surface evaporation reduced where a crust exists -Crusts decrease water loss because less of their surface area is exposed to the air compared to a tilled, fluffy soil. In addition, a crust forms a barrier to evaporation of soil moisture. Reduced evaporation of soil moisture means more water remains in the soil for plant use. • Harvesting, burning, burying, or otherwise removing plant residues and mulches so as to leave the soil surface bare for an extended period of time, and • Soil disturbing activities that destroy organic matter, soil structure and aggregation, and result in very smooth seedbeds

Problems with Poor SS + MP

-runoff, erosion, surface crusting -poor germination and seedling emergence • Disturbance that exposes soil to the adverse effects of higher than normal soil drying, raindrop and rill erosion, and wind erosion • Conventional tillage and soil disturbance that accelerates organic matter decomposition • Residue harvest, burning or other removal methods that prevent accumulation of soil organic matter • Overgrazing that weakens range and forage plants and leads to declining root systems, poor growth and bare soil • Equipment or livestock traffic on wet soils • Production and irrigation methods that lead to salt or sodium accumulation in surface soils

Aggregate Stability

-soil aggregates: groups of soil particles that bind to each other more strongly than to other surrounding particles -aggregate stability: ability of soil aggregates to resist disintegration when disruptive forces associated with tillage and water or wind erosion are applied

Inherent Factors Affecting Available Water Capacity

-soil texture, presence and abundance of rock fragments, and soil depth and layers. -increases with increasingly fine textured soil, from sands to loams and silt loams. Coarse textured soils have lower field capacity since they are high in large pores subject to free drainage. Fine textured soils have a greater occurrence of small pores that hold water against free drainage, resulting in a comparatively higher field capacity -in comparison to well-aggregated loam and silt loam soils, the available water capacity of predominantly clay soils tends to be lower since these soils have an increased permanent wilting point -Rock fragments reduce available water capacity of soil proportionate to their volume, unless the rocks are porous -Soil depth and root restricting layers affect total available water capacity since they can limit the volume of soil available for root growth.

Dynamic factors affecting aggregate stability

-stability increases w organic matter and bio activity in soil -fungal hyphae bind soil particles to form aggregates -earthworms secrete binding materials -particles can be aggregated by "glue" formed during the decomposition of organic matter -physical disturbance accelerates decomposition and destroys fungal hyphae and soil aggregates

Relationship of Bulk Density to Soil Function

-structural support, water and solute movement, and soil aeration -bulk density above 1.8 g/cm3 in sandy soil, 1.65 g/cm3 in silty soil, and 1.47 g/cm3 in clay soils restrict root growth -ideal bulk densities are below 1.6 g/cm3 for sandy soils, 1,4 g/cm3 for silty soils, and 1.1 g/cm3 for clay soils -used to express soil physical, chemical and biological measurements on a volumetric basis for soil quality assessment and comparisons between management systems

Relationship of SS + MP to Soil Function

-sustaining biological productivity, regulating and partitioning water and solute flow, and cycling and storing nutrients. Soil structure and macropores are vital to each of these functions based on their influence on water and air exchange, plant root exploration and habitat for soil organisms.

Slaking

-the breakdown of large, air-dry soil aggregates (>2-5 mm) into smaller sized microaggregates (<0.25 mm) when they are suddenly immersed in water -Slaking occurs when aggregates are not strong enough to withstand internal stresses caused by rapid water uptake. Internal stresses result from differential swelling of clay particles, trapped and escaping air in soil pores, rapid release of heat during wetting, and the mechanical action of moving water -In contrast to slaking, tests for aggregate stability measure how well soil withstands external destructive forces, such as the splashing impact of raindrops. Both poor aggregate stability and slaking result in detached soil particles that settle into pores, and cause surface sealing, reduced infiltration and plant available water, and increased runoff and erosion.

Infiltration

-the downward entry of water into the soil -The velocity at which water enters the soil is infiltration rate. Infiltration rate is typically expressed in inches per hour

Problems w Poor Aggregate Stability

-unstable aggregates disintegrate during storms -Dispersed soil particles fill surface pores and a hard physical crust can develop when the soil dries. -infiltration reduced -highly erodable -Tillage methods and soil disturbance activities that breakdown plant organic matter, prevent accumulation of soil organic matter, and disrupt existing aggregates, • Cropping, grazing, or other production systems that leave soil bare and expose it to the physical impact of raindrops or wind-blown soil particles, • Removing sources of organic matter and surface roughness by burning, harvesting or otherwise removing crop residues, • Using pesticides harmful to beneficial soil microorganisms.

Measuring Slaking

2. Take several (at least three) small (3 to 5 mm diameter) crumbs of dry soil and place them in a dish or saucer of rainwater (or distilled water) deep enough to completely cover the samples. 3. Cover the dish to prevent wind from disturbing the water. 4. Assess the slaking score (0-4) after 5 minutes. After five minutes, score slaking as follows: Score 0 if the lump remains intact Score 1 if the lump collapses around the edges but remains mainly intact Score 2 if the lump collapses into angular pieces Score 3 if the lump collapses into small (less than 2 mm diameter) rounded pieces, forming a cone Score 4 if the lump collapses into single grains (you can see sand grains).

Measuring Bulk Density

A metal cylinder is pressed or driven into the soil. The cylinder is removed, extracting a sample of known volume. Alternatively, for subaqueous samples taken as vibracores and opened by cutting, a plastic syringe with the end removed is used to collect a mini-core. The plunger can be fixed at the 10-ml volume mark and the syringe gently pushed into the split vibracores sample to collect a known volume of sample. The moist sample weight is recorded. The sample is then dried in an oven and weighed.

Relationship of Soil Crust to Soil Function

A surface crust indicates poor infiltration, a problematical seedbed, and reduced air exchange between the soil and atmosphere. It can also indicate that a soil has a high sodium content that increases soil dispersion when it is wetted by rainfall or irrigation

Measuring Soil Crusting

Crust air-dry rupture resistance can be measured by taking a dry piece of the crust about ½ inch on edge and applying a force on the edge until the crust breaks. Generally, more force is required for crusts that are thick and have high clay content. A penetrometer to measure the penetration resistance of the crust can be used. Crust thickness can also be measured

Relationship of Infiltration to Soil Function

Infiltration is an indicator of the soil's ability to allow water movement into and through the soil profile. Soil temporarily stores water, making it available for root uptake, plant growth and habitat for soil organisms.

Relationship of Slaking to Soil Function

Slaking indicates the stability of soil aggregates, resistance to erosion and suggests how well soil can maintain its structure to provide water and air for plants and soil biota when it is rapidly wetted. Limited slaking suggests that organic matter is present in soil to help bind soil particles and microaggregates into larger, stable aggregates

Dynamic Factors Affecting Slaking

Soil organic matter promotes aggregate formation and stability of bound aggregates. Repeated tillage prevents accumulation or results in loss of organic matter and causes soil aggregates to breakdown into finer particles. Since loss of organic matter reduces aggregate stability, slaking increases as organic matter decrease

Measuring Infiltration

The single ring infiltrometer involves driving a single metal ring partially into the soil and filling it with water. Double ring infiltrometers in contrast require two rings (inner and outer), which creates a one dimensional flow of water from the inner ring. The inner ring is driven into the ground, while a second larger ring is located around the smaller one in order to help control the flow of water through the first ring. In both cases the rate at which the water moves into the soil is measured by recording how much water goes into the soil for a given time period. This rate becomes constant when the saturated infiltration rate for the particular soil has been reached. The rate at which water goes into the soil is related to the soil's hydraulic conductivity (or ease with which water can move through pore spaces or fractures). The difference between the single ring and double ring methods is that with single ring infiltrometers, water spreads laterally as well as vertically making the analysis more difficult.

Improving SS + MP

• Cover Crop • Conservation Crop Rotation • Irrigation Water Management • Prescribed Grazing • Residue and Tillage Management • Salinity and Sodic Soil Management