Stoichiometry and Nutrient Availability
What is ecological stoichiometry and what does it mean for an organism to be “limited” by a given nutrient (e.g. C, N, or P)?
“The idea that organisms generally require elements in some ratio (e.g. C: N:P of 60:7:1 in soil microbial biomass)."
What are the major types and causes of soil degradation, and hat human activity is most commonly associated with soil degradation?
1. Water washing away or carrying away looser soil particles
2. Effects of gravity on conventional tillage practices
3.The action of wind on dry exposed soil
Agriculture is the human activity that contributes the most to soil erosion by weakening soil structure. Promotes wind and water erosion.
Once inside an ecosystem, what is the most common “circuit” that a nitrogen or phosphorus atom will travel?
SOM -> decomposers -> mineral N or P -> plants -> SOM.
What are cover crops and how do they help regenerate soil?
Cover crops, also known as green manure are crops planted without the purpose of human consumption or processing.
Keeping plants in soil as much as possible helps maintain biota and structure, keeps soil ‘alive’
Help bolster organic matter in soil
Legumes planted can increase available nitrogen
Tillage destroys organic matter over long term so this can amend OM losses
Provides pollen for beneficial predatory insects (wasps)
Increases biodiversity in soils
Rotations can help the nutrient cycling of N
What are the problems associated with the loss of soil biodiversity and how can a farmer increase soil diversity?
Loss of biodiversity can diminish ecosystem function and resilience. "In addition to using cover crops and perennial crop species as described above, soil biodiversity improves with the use of diverse crop polycultures and integrated pest management."
What is nitrogen mineralization and why is it so important?
“...bacteria will be limited by the availability of carbon in the soil organic matter and will thus “excrete” or “release” mineral nitrogen as a waste product."
Nitrogen mineralization via bacteria is one of the main ways organic nitrogen is converted into a form that is able to be taken up by plants.
What are the four processes that – together with gravity and the inescapable up/down nature of soil – lead to soil horizons?
Additions: rain, organic material (leaves, animal droppings)
Losses: gaseous loss, harvest, leeching, etc
Translocations: something moves but it doesn't change its nature. e.x.Moving from one horizon to another
Transformation: e.x. Decomposition. Form is changed, oxidation/reduction
What is the “immobilization” of nitrogen or phosphorus?
The N or P is no longer “mobile” and able to be taken up by plants because it has been taken up my microbes (i.e. fungi or bacteria or archaea).
What are the problems associated with tillage and what is “no-till” farming?
“Over long periods, tillage greatly hastens the oxidative loss of soil organic matter, thus weakening soil aggregates. Tillage operations, especially if carried out when the soil is wet, also tend to crush or smear soil aggregates, resulting in loss of macroporosity and the creation of a puddled condition.”
“Technology that directly drills seeds into the soil without having to turn the soil over has allowed the advent of no-till farming. The huge benefit is that soil structure is maintained (recall that real soil has an “up” and a “down”; tillage destroys this), which supports aggregation and water infiltration. One important tradeoff is that in order to deal with weeds, most large no-till operations use more herbicide than tillage operations.”
What are CaFO’s and why are they so problematic?
Concentrated animal feeding operations (CAFOs, aka “factory farms”).
"Whereas on integrated farms the animal waste was a resource that could help maintain soil health, the animal waste from CAFOs is more akin to industrial pollution that has to be dealt with. Farm animals in the US produce ten times as much waste as humans overall!"
What does it mean to say an organism (e.g. plants, soil microbes) is “carbon limited” or “nitrogen limited” or “phosphorus limited”?
The food that organisms consume consume seldom has the precise ratio that they require.
The nutrient an organism is limited by is the one they are not in excess of, and is therefore needed to facilitate further growth and reproduction.
What are the four USDA soil orders we have been using in all of our in-class analyses and what are their general characteristics and the contexts in which they tend to form?
-Alfisols-subsurface silicate clay accumulation, under deciduous forest, high fertility. Strong weathered soils found in good to hot humid areas
-Histosols: consists of most OM, abundant fibric (peats and mucks). Roots and rhizomes of marsh grasses. Form in wetlands with limited drainage. Highest in carbon storage.
-Mollisols: soil of grassland prairie ecosystem. Accumulation of Ca rich OM. Found in middle latitudes. High productive agricultural soils. Dominate US great plains.
-Spodosols: acidic soil with accumulation of humus with Al and Fe content. Not agriculturally productive. Prevalent in northern parts of US-great lakes region. Form mostly in coniferous (e.g. pine, spruce, cedar) forests.
What are the major inputs and outputs of nitrogen to terrestrial ecosystems and how do those impact nitrogen availability over geologic time?
1. The largest input to the local nitrogen cycle comes from the activities of nitrogen-fixing bacteria…takes place in the nodules of “nitrogen-fixing” plants. Relatively few plant species are “nitrogen fixing.”
2. Industrial fertilizer. Between fertilizer and the planting of nitrogen-fixing crops, humans have DOUBLED nitrogen inputs to terrestrial ecosystems.
3. Lighting breaks the triple bond of dinitrogen gas and causes mineral nitrogen to rain down on the soil…smaller input than either nitrogen fixation or fertilizer.
1. Denitrification is an important nitrogen loss pathway…anaerobic denitrifying bacteria use nitrate as an energy source in low-oxygen conditions and produce dinitrogen gas, releasing nitrogen from the soil.
2. Leaching is another important nitrogen loss pathway. Very little ammonium (NH4+) is lost via leaching because it tends to electrostatically stick to negatively charged clay particles. In contrast, nitrate (NO3-) can get flushed out in a rain event. Mainly effects agricultural areas.
What are the advantages of perennial agriculture over annual agriculture?
“...perennial crops minimize the number of times the farmer needs to disturb the agroecosystem, and perennials cover the soil year round”
Why is soil compaction problematic and what solutions exist to address it?
“Poor water infiltration leads to standing water at the soil surface and little water storage in the soil. Poor aeration leads to anaerobic decomposition. Tight, compacted soil makes it difficult for roots, earthworms, and other burrowing organisms to move through the soil. With less activity from aerobic soil organisms, soil aggregation suffers, which does nothing to help with water retention or aeration.”
“There is very little that can be done to “uncompact” compacted soil. Soil compaction is best avoided by keeping planted areas separate from areas with foot or machinery traffic and by avoiding the use of machines when soils are saturated and more liable to compact. That said, tough- and deep-rooted plant species grown as cover crops or on fallowed land may slowly work to loosen compacted soil particles.”
How does soil pH affect nutrient availability for plants?
Different compounds and elements are more or less soluble at varying pH’s, you want to maintain a pH where nutrients are accessible.
Many heavy metals sit on more acidic or basic sides on the pH scale, making it important to monitor if you are concerned about the bioavailability of pollutants in your soil.
What are the general soil horizons O, A, B, C, & R, and what are their basic characteristics?
O:Top most and darkest layer. Organic matter accumulation is the first step in soil formation. Organic layers, plants, leaves, animal residues, initial decomposition. O Sub Horizons-organic fibric materials with recognizable plant and animal parts.
A: Topmost mineral horizon, dark brownish layer, coarser. (More recognizable in grassland vegetation with sandy soils)
(Predominant in arid and semiarid regions)
Reduced biological activity, carbonates and gypsum accumulation.Predominant in rock like soil. Less weathered plant material.
R: Consolidated rocks. Little evidence of weathering. None to very reduced biological activity. e.x. rockbeds
What are the major inputs and outputs of phosphorus to terrestrial ecosystems and how do those impact phosphorus availability over geologic time?
1. The largest input to the local phosphorus cycle comes from the weathering of rock (a.k.a. “parent material”). That is why geologically young soils have so much usable phosphorus; the parent material is close to the surface and loaded with phosphorus atoms that keep getting weathered out.
2. Airborne rock dust from deserts (especially the Sahara) can make it into the upper atmosphere and then precipitate out far away.
3. Humans have also increased phosphorus availability by adding mined phosphorus fertilizer to farmland.
1. The main “output” of phosphorus is occlusion: phosphorus-containing molecules become so tightly bound with soil particles that no living thing can liberate them…Those phosphorus atoms will have to wait…to become compressed into rock in the Earth’s crust and then lifted back to the surface as part of the mountain-building processes of plate tectonics…millions of years later, the phosphorus atoms can again weather out of the parent material and begin another few centuries circulating around a local ecosystem before they are again occluded.
2. Leaching of phosphorus is less important than leaching of nitrogen..mineral phosphorous is less mobile in soil than mineral nitrogen. However, when farmers apply lots of mineral phosphorus fertilizer, a lot can leach out and impact groundwater and surface waters.
What is Integrated Pest Management and how does it benefit soil?
“integrated pest management seeks to minimize the use of pesticides by promoting habitat for natural enemies and by using targeted applications of more benign chemicals only as a last resort. Soil organisms benefit from the reduction of toxins that find their way into the soil.”
What solutions help with soil contamination by herbicides, pesticides, heavy metals, and industrial chemicals? Can you explain how phytoremediation is related?
“...many of the physical, chemical, and biological processes that naturally take place within the soil can degrade soil contaminants, given enough time. Heavy metals can sometimes be immobilized by binding to soil chemicals and thus be made less hazardous. However, with other chemicals or under other soil conditions, contaminated soils must be remediated. Until recently, this was almost always done with heavy-handed industrial chemistry,”.
Phytoremediation is the use of photosynthesizing plants to remediate contaminated soils. “Phytostabilization is the use of contaminant-tolerant plant species to provide cover and thus minimize erosion. A more aggressive form of phytoremediation is the use of hyperaccumulator plant species, i.e. plant species that tend to take up and tolerate the contaminant in relatively large concentrations. In effect, the hyperaccumulator acts like a chemical sponge, pulling the contaminant out of the soil. Then the plant biomass can be harvested and burned or otherwise stored safely.”
What is the "sweet spot" pH for fertile soils?
A pH of 6.0-8.0 is the sweet spot in which most nutrients can be taken up by plants.
Explain the ways each of the components of CLORPT (climate, organisms, relief, parent material, and time) can influence soil development.
Organisms: activity and molecular makeup of vegetation, soil biota, soil animals, and humans-The type of vegetation influence OM accumulation, and acts as an input food source for biota.
Relief: slope, aspect, landscape position, topography. Aspect=orientation in relation to the sun, affects absorbance of solar energy.
Parent Material: input materials/types of rock/erosion cycles. Geological processes bring parent materials to the earths surface. Can greatly impact biota and soil structure.
Time: how long has soil development been taking place? Weathering of rock creates 0.01-0.1mm of new soil material a year. All other factors are influenced by time
Why is decomposition so important to nitrogen and phosphorus cycling?
Decomposition is crucial to nitrogen and phosphorus cycling as it makes these nutrients accessible to plants and thus available for reuse in ecosystems. During decomposition, microorganisms break down complex organic compounds, liberating nitrogen and phosphorus in mineralized forms that plants can uptake. This facilitates the recycling of nitrogen and phosphorus, which is essential for sustaining plant growth, ecosystem productivity, and overall nutrient balance.
What is biochar? Is all biochar basically the same? What two big factors can lead to biochar with different properties? How can biochar help improve soil health?
“Biochar is what remains after organic matter (e.g. wood, grass) is combusted with very little oxygen at intermediate temperatures (i.e. “pyrolysis”). Biochar is rich in carbon and can persist in soils for centuries.”
“... it is important to note that no two biochars are the same. Why? First, the temperature and oxygen concentration of pyrolysis has a huge impact on the biochar’s surface area, pH, and associated properties. Second, different feedstocks (i.e. biomass sources) yield very different biochar properties even under identical conditions of pyrolysis.“
What is manure? What are biosolids? What is compost? How can these help manage soil nutrients?
Manure- Non-human animal waste processed and applied for agricultural purposes to crops.
Biosolids- "Biosolids are not human excrement. Rather, biosolids are the waste of microbes (mainly bacteria and archaea, I believe) that have consumed human excrement in the wastewater treatment facility."
Compost: Organic waste that has been decomposed intentionally and aerobically to be used as a soil amendment.
All of these help return nutrients back to the soil.