Lecture 3 Soil Engineers Learning Objectives Lecture 3 – Soil Engineers Lecture 3 – Soil...
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Transcript of Lecture 3 Soil Engineers Learning Objectives Lecture 3 – Soil Engineers Lecture 3 – Soil...
Lecture 3Soil Engineers
Learning Objectives• Lecture 3 – Soil Engineers– Explain why earthworms, ants and termites
are called soil engineers– Describe earthworms as an example for the
importance of functional diversity and the impact of invasive species (both negative and positive)
– Discuss the benefits of managing soil to encourage a healthy, diverse soil community.
Lecture 3 - Topics• Intro Soil Engineers• Earthworms• Summary of Soil Organisms
Organisms that make major alterations to the physical environment that influences the habitats for many other
organisms within the ecosystem
Ecosystem Engineers
• Microorganisms that create impermeable surface microbiotic crust that spatially concentrates scarce nutrient and water supplies in certain arid and semi-arid ecosystems.
• Burrowing animals that create air and water movement in soil as well as create root passages through dense surface soils. Earthworms are “nature’s tillers”. Ants and termites create passage ways and mounds.
• Humans
What Do Earthworms Do?
1. Stimulate microbial activity• Earthworms derive nutrition from microbes• Organic matter is fragmented and inoculated
in gut• Greater microbial biomass in feces and casts
than in surrounding soil – microbial hotspot
http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
What Do Earthworms Do? (cont)
• Soil passed through the earthworm gut is expelled as “casts”.
• During the passage through the gut, organic materials are shredded and mixed with mineral soil materials. The casts enhance the aggregate stability of the soil.
• Carry organic matter down into deeper soil layers
2. Mix and aggregate soil
What Do Earthworms Do? (cont)3. Increase infiltration4. Improve water holding capacity
http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
Burrow
• Increase porosity• Burrows become preferential
flow paths • Help minimize surface water
erosion• By fragmenting organic matter
and increasing soil porosity and aggregation - earthworms improve water holding capacity
What Do Earthworms Do? (cont)1. Stimulate microbial activity2. Mix and aggregate soil3. Increase infiltration4. Improve water holding
capacity5. Provide channels for roots
growth6. Bury and shred plant residue
http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
Pulling corn leaf into burrow
Earthworm Functional Diversity
http://www.nrri.umn.edu/worms/identification/ecology_groups.html
EpigeicSurface soil and
litter species
EndogeicUpper soil species
AnecicDeep burrowing
species
Earthworm Video
www.bbc.co.uk/nature/life/lumbricidae#p00thgkz
Abundance and Distribution
Native Earthworm Distributions
(Proulx 2003 risk assessment of non-indigenous earthworms)
The majority of temperate and many tropical soils
support significant earthworm populations
Abundance and Distribution
Native Earthworm Distributions
(Proulx 2003 risk assessment of non-indigenous earthworms)
L. terrestrus and L. rubellus
Invasive Earthworm Distributions
Active Invasion on Local Scales
(Bohlen et al. 2004, Ecosystems) L. rubellus in Cornell’s Arnot Forest, NY Box 10.1
in text
Smithsonian Forest
3 old forest sites (120-150 y)
3 young forest sites (50-70 y)
Macroinvertebrate activityLitter decayOrganic matter inputs
Dominant earthworms
Late
Mid
• Consume litter layer, can leave 60% of soil surface bare
• Even when native earthworms are present, invasives make major alterations to the soil environment
Earthworm biomass (g/m2)
Successional Stage(Filley et al. 2008, Global Biogeochemical Cycles)
L. rubellus
10
20
30
40
50
60
0
Invaded Forests• Biomass and density was high• Species diversity was low• Functional diversity was low
Earthworms and Agriculture
• Croplands in the US can contain 50-300 earthworms/yd2 • Grasslands and temperate forests can have 100-500
earthworms/yd2• Based on total biomass, earthworms predominate
the soil invertebrates
Lumbricidae is the most important family of earthworms enhancing agricultural soils*.
Only 2 species are native,the rest are from Europe and Asia
Putting Invasives to WorkBUG BIOGRAPHY: Night Crawlers and Tillage
The substitution of conventional tillage by no-till or conservation tillage is increasingly common and widely adopted in the United States and elsewhere. In these situations, earthworms, particularly the “night crawler,” Lumbricus terrestris L., are especially important. Earthworms become the main agent for incorporating crop residue into the soil by pulling some into their burrows and by slowly burying the remainder under casts laid on the soil surface.
In reduced tillage systems, surface residue builds up and triggers growth in earthworm populations. Earthworms need the food and habitat provided by surface residue, and they eat the fungi that become more common in no-till soils. As earthworm populations increase, they pull more and more residue into their burrows, helping to mix organic matter into the soil, improving soil structure and water infiltration.
http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
Summary – Ecosystem Engineers• Organisms that make major alterations to the
physical environment that influences the habitats for many other organisms within the ecosystem
• Earthworms dominate the soil invertebrates, occur at every trophic level– Native populations are biodiverse, species and
functional diversity– Invasive populations are more likely to have greater
biomass but less diversity– Invasive earthworms can be damaging in forest floors
but beneficial in some agricultural systems
Summary – It’s Alive• Soil is a complex, diverse ecosystem
‒ Organisms incorporate plant residues into soil, return CO2 to the atm where it can be re-fixed into plants. In the process, soil organic matter is formed and essential plant nutrients are released.
• 80-90% of metabolic activity in soil food web is bacteria and fungi• The activity of organisms is more important
than the identity. Functional diversity vs. species diversity.
Summary – Beneath the Surface• Rhizosphere• Hyphae• Mycorrhizae• Biological N fixation– Inoculants to be sure that crops have the
right symbiosis cost $3 /ha; fertilizer costs $87 /ha
– Nearly as much N fixed into fertilizers than BNF annually
Summary – Soil Organisms• In every healthy system or watershed, the soil food web
is critical to major soil functions– Sustaining biological diversity– Regulating flow of water and dissolved nutrients– Storing and recycling nutrients and elements– Filtering, buffering, degrading, immobilizing, detoxifying
potential pollutants • Complexity, that is, interactions among organisms and
high functional diversity within the soil food web, enhances these functions
• Microorganisms and earthworms dominate the life of most soils (Table 10.4)