Why Is Soil Quality Important?

Beyond Plants – Indicators and Soil Surface Properties in STM’s

Arlene Tugel Soil Scientist – Liaison to ARS USDA-NRCS Las Cruces, NM Soil degradation can affect:

• Plant production, reproduction and mortality • Erosion • Vegetation changes • Establishment and growth of invasive plants • Water yields and water quality • Air quality • Wildlife habitat • Carbon sequestration Transitions

Cause of transition Accelerating practice Directional climate ?? Redefine potential change Soil degradation Increase root biomass

Altered hydrology Gully plugs, create meanders

Competitor Selective herbicide application establishment Depletion of seed pool Seeding

Catastrophic fire Seeding, selective herbicides Disturbances, function, soil resistance and resilience Compaction Soil with disturbance high resistance

Low resistance

Soil function and high Low resistance and (% of capacity) resilience low resilience

Time (years) (Seybold, et al., 1999) Transitions: Soil degradation processes after disturbance • Organic matter loss •Erosion • Reduced biological activity • Nutrient depletion • Nutrient depletion • Structural degradation • Crusting, sealing • Decreased porosity • Compaction • Increased bare spaces • Increased soil temperature • Salinization • Water-logging/artificially drained • Fire-induced water repellency Using indicators to detect soil degradation • Indicator: “A soil or plant property that is sensitive to change.”

• Reflects complex processes that are too difficult or costly to measure. – Primary ecological processes (nutrient cycling, energy flows, water cycle) – Degradation processes

• Gives a snapshot in time.

ProcessesProcesses andand indicatorsindicators • Soil organic matter • Bulk density/porosity Affect • Aggregate stability infiltration • Surface crusts Rain

Infiltration

Soil Runoff Storage

Hydrologic function Dynamic soil properties

are ators y indic rties = soil properties that ualit pe oil q soil pro S mic change over the dyna human time scale.

0 - 20 cm

Decades = management 3.5 time scale 3 2.5 Decades to centuries = (kg/m2) recovery time scale 2

Soil Organic Carbon Carbon Soil Organic 1750 1800 1850 1900 1950 2000

Redrawn from Hibbard, 1995 Plant community changes affect soil organic matter and soil quality

Grass displaced by shrubs Topsoil and Soil surface fertility organic lost, matter infiltration decreases decreases and size of and soil water Aggregate bare spaces decreases stability and increases resistance to erosion decrease Process indicator: Black grama grassland: 42% canopy cover proportion of soil surface covered by large gaps

Mesquite shrubland: 38% canopy cover Calibration example (gap intercept method)

Wind erosion Threshold Velocity for Saltation

thresholds are 60 often crossed 40 during shrub invasion as gap 20 km/h @ 2m 0 sizes increase 0 500 1000 1500 2000 2500 Gap Diameter (cm) Management-plant-soil interactions drive transitions

Root distribution Grazing pressure

S1-UG (Intact) S1-LG (Stable) S1-SG (Degrading) S2-HG (Degraded) 0 4 0 20 30 4 0 3 1

Soil depth (cm)Soil depth 0 2 -10 0 0 3 2 0 0 20 1 0 1 1 0 -20 0

-30

-40 0 5 10 15 20 5101520 5 101520 5101520 Distance from plant center (cm)

Fig. 4. Root distributions (mm2/cm3 soil) within soils of tropical tallgrass sites in response to accumulated grazing pressure.

Norfolk, et. al. 2001 Soil organic matter

Soil Organic Matter TYPE RATE OF FUNCTION DECAY

Short term Light Weeks to • Serves as food for soil organisms fraction months • Stores and provides plant nutrients

Physically Decades • Enhances soil structure and protected porosity and water holding capacity

Chemically Hundreds • Hold nutrients Long term stable to • Stabilizes micro-aggregates thousands • Gives soil its dark color of years

Biotic Integrity Organic matter and nutrient cycling Soil and Site Stability Organic matter and soil aggregates: bound together by fungi, root exudates and “glues” (polysaccharides) secreted by bacteria Hydrologic function Organic matter, physical characteristics and water

Physical crusting

Infiltration and runoff Biological crusts may be important for: surface roughness/infiltration, soil stability, and nutrient cycling. Excessive traffic compacts soil.

• Soil compaction and physical crusting reduce water infiltration. • This can increase erosion and reduce water available for plants. • Subsoil compaction can reduce rooting depth. Erosion patterns

• Rills • Gullies • Water flow patterns • Wind scour • Pedestals • Terracettes State and Transition Models and Narratives

•• STATESTATE -- aa complexcomplex ofof twotwo ecosystemecosystem components,components, thethe soilsoil basebase andand vegetationvegetation structure.structure. –– SoilSoil formationformation determinesdetermines thethe sitesite’’ss capability.capability. –– InteractionInteraction betweenbetween soilsoil andand vegetationvegetation determinesdetermines functionalfunctional statusstatus ofof thethe site.site. Stringham, et al., 2001, 2003 Rates of degradation may vary among soil series correlated to one Ecological Site (even though they have similar HCPC and dynamics)

Burrograss-Mesquite Loamy SD-2

Tobosa-Mesquite

Typic Calciargid, Dona Ana % carbonates 0-30 cm =7.7 % clay 0-30 cm = 18.4

Tarbush-Burrograss Typic Calciargid, Berino % carbonates 0-30 cm =0.2 % clay 0-30 cm = 25.7

Degraded states are more frequent on Dona Ana soils than on Berino soils Transitions may not involve dramatic changes in vegetation

Nickel series, MLRA 42, typic aridic Gravelly Dark A Light A

Grassland absent for Recent grassland loss, decades, recovery potential unlikely for recovery Already crossed a soil Crossed a biotic degradation threshold threshold, soils not yet degraded

The dynamic relationship between soil and vegetation is key to defining thresholds 1. Use indicators to help determine transitions and states. Need to understand cause and affect.

• What are management affects on soil and plants, aka on ecological processes?

• How do plant community shifts affect soil properties (dynamic soil properties)?

• How do shifts in dynamic soil properties affect plant communities? 2. Include specific soil degradation process when choosing and describing mechanisms of change. Organic matter loss Reduced biological activity Structural degradation Crusting, sealing Decreased porosity Compaction Increased soil temperature Nutrient depletion Salinization Water-logging Fire-induced water repellency Erosion 3. Strategies for the Text - Add descriptions of rangeland health/soil quality indicators How do we distinguish the states and communities? • Diagnosis: Grass cover is fairly uniform with few large bare areas present. Mature piñon and/or juniper are an important component of the site with canopy averaging 25 percent. Evidence of erosion such as pedestalling of grasses, rills and gullies are infrequent.

• From MLRA-36, WP-2: Savannah, David Trujillo, author

• Why we think this is good: • 1) Descriptive • 2) Refers to data • 3) Refers to rangeland health indicators Where do I get more information on soil quality indicators? monitoring biological crusts

2. Assessment and 3. Aggregate stability 4. Compaction 5. Infiltration 6. Organic matter 7. Physical and 8. Soil biota 9. Water erosion 10.Wind erosion

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Rangeland Soil Quality— Soil Rangeland Soil Quality Information Sheet Information Quality Soil Rangeland soil quality Information Rangeland Sheet 6

Soil Quality Information Sheet sheets Rangeland Soil Quality—Organic Matter USDA, Natural Resources Conservation Service May 2001

What is soil organic matter? Soil organic matter is carbon-rich material that includes plant, animal, and microbial residue in various stages of decomposition. Live soil organisms and plant roots are part of the carbon pool in soil but are not considered soil organic matter until they die and begin to decay. The quantity and composition of soil organic matter vary significantly among major ecosystems. Soil in arid, semiarid, and hot, humid regions commonly has less organic matter than soil in other environments. The total content of organic matter ranges from less than 0.5 to more than 8 percent in the surface layer of rangeland soils. Soil organic matter includes three main components (table 1). The light fraction is more biologically active than the other two and includes relatively fresh plant fragments. Physically protected organic matter is locked within aggregates of mineral particles, where it is protected from microbial decomposition. Organic mattter darkens and stabilizes the surface layer in soils. Chemically stable organic matter gives soil its dark color and is generally the largest pool of organic matter in soil. Physically • enhances soil fertility and plant productivity by improving protected organic matter may also be chemically stable. the ability of the soil to store and supply nutrients, water, Table 1.—Soil organic matter and air; • provides habitat and food for soil organisms; Component Rate of Primary function • sequesters carbon from the atmosphere; decay • reduces mineral crust formation and runoff; and • reduces the negative water quality and environmental Light fraction Weeks to • Serves as food for soil effects of pesticides, heavy metals, and other pollutants by • What is soil organic matter?months organisms actively trapping or transforming them. • Stores and provides plant nutrients What affects soil organic matter? Physically Decades • Enhances soil structure, protected porosity, and the water-holding The amount of organic matter in the soil is a balance between • Why is it important? capacity additions of plant and animal materials and losses through decomposition and erosion. Chemically Hundreds to • Holds nutrients Environmental factors interacting over time affect the stable thousands • Stabilizes microaggregates amount of organic matter in soil. Rainfall and temperature affect of years plant productivity and the rate of organic matter decomposition. Increasing levels of organic matter promote a higher water- • How is it measured? Why is organic matter important? holding capacity, which results in increased plant growth and thus an increased amount of organic matter and plant nutrients. Soil organic matter enhances soil functions and Roots are the primary source of organic matter. Dead roots environmental quality because it: and gelatinous materials exuded by plant roots as they grow • binds soil particles together into stable aggregates, thus through the soil are decomposed by soil organisms and improving porosity, infiltration, and root penetration and converted into organic matter. Since much of what is produced • What affects it? reducing runoff and erosion; above ground is lost through photo-oxidation, the amount of • Management strategies Chemical indicators may also be important • Active carbon • Soil nutrients • Carbonates • Electrical conductivity/salinity • Sodicity • Cation exchange capacity • Soil contaminants Qualitative soil methods

Soil stability kit

Infiltration

Aggregate stability Samples for Bulk density Organic carbon Penetrometer pH, EC SAR, etc Soil and vegetation change: Dynamic soil properties and STM’s

Soil survey today: Need multiple values Only one set of based on management values exists for all (states) land uses (1) (2) Dynamic Properties (Use-dependent) (3) (4)

Static Properties (5) Tilled (6) No-till Cropland Cropland Summary

1. How well a soil (site) functions is related to the effect of soil degradation on primary ecological processes. 2. Consider differences in near-surface soil properties as clues to identification of states. 3. Remember that different soils can respond differently to the same disturbance 4. Include soil dynamics in STM’s. 5. Soil scientists have a role in developing and describing STM’s • Rangeland Health: “The degree to which the integrity* of the soil, vegetation, water, & air as well as the ecological processes of the rangeland ecosystem are balanced and sustained.”

•* “Integrity is the maintenance of the functional attributes characteristic of a locale, including normal variability”