Soils Part One Flashcards
In addressing soil problems, you are trying to…
Improve tilth
Increase beneficial organisms, which will
Increase humus content and
Improve plant health and resistance to diseases and pests, while also
Correcting soul nutrient imbalances and
Detoxifying soil and
Reducing weeds
Soil consists of…
Mineral solids, sand silt and clay
-mainly consist of Si, O, Al, K, Ca, Mg
Soil Water, soil solutions
-main source of water and makes available essential nutrients
Air
-Provides O and helps to remove CO2
Aggregates
-mineral and organic particles clumped together, creating spaces, or pores, to allow for water storage and gas respiration
Soil texture and organic matter
Fine (high clay and silt) tend to have more om than course (sands / sandy loams). OM ranging from less than 1% to more than 5%.
Also, the higher the clay and silt contents the more om is needed to produce stable aggregates, because more is needed to occupy the surface sites on the minerals during the process of om accumulation.
Reason: strong chemical bonds between clay/silt and om protect from attack and decomposition by micro organisms. They combine to form aggregates that also protect om from micro organisms. Smaller pores and this less oxygen.
Soil erosion and Organic Matter
OM as surface residues or as a binding agent for aggregates near the surface decrease erosion by
Intercepting raindrops and decreasing their potential to detach soil particles
Slowing water across the field, improving chance of infiltration
Soil compaction, aggregates and organic matter
As OM increases, compaction decreases and spaces for air and water increase.
Sticky substances are produced by decomposed plants. Along with plant root ands and fungal hyphae, they bind mineral particles together into clumps, or aggregates. Also, sticky substances of mycorrhizal fungi are an important binding material in soil
Large pore formation and benefit
Increases ability to absorb and increase flow of water.
Formed by old root channels, large soil organisms (insects and worms) as they move around and excrete mucus
PH balance and organic matter
OM slows and buffers changes in ph by taking free radical hydrogen out of solution as acids are produced or by giving off hydrogen as bases are produced
At lower ph, Om decomposition is slower and lower worm activity means it’s less distributed through layers
Soil color and organic matter
OM tends to darken soils, and under well drained conditions, this allows soil to warm up a little faster in the spring (beneficial for cold regions).
Nitrogen and organic matter
All of soil N exists as part of OM. Bacteria and fungi convert organic forms of N into ammonium, and different bacteria convert ammonium in nitrate, both of which are usable by plants
Weather/climate and organic matter
Higher temps lead to lower OM. More vegetation is produced, but decomposition rate increases and is dominant factor.
OM generally increase with higher precipitation due to higher vegetation growth and lower decomposition from lower aeration.
Nutrients and organic matter
Directly
Increase availability
-decomposition, mineralization (organic converts to simpler inorganic forms)
- chelates protect nutrients from binding with others (iron, aluminum)
Increase storage
- increased humus and om increases negative exchange sites, or CEC, to Ca, K, Mg, and NH4+ (ammonium).
Indirectly
- micro organisms produce substances that help root growth and health, which means easier access and ability to absorb nutrients.
- Micro organisms also free nutrients from organic molecules and fix nitrogen.
- greater water retention, improving plant health and growth and increasing mobility of nutrients
Tillage and organic matter
Impacts both the amount of topsoil erosion and rate of om decomposition.
Note
- conventional tillage and disking to prepare a smooth seedbed break down natural soil aggregates and destroy large water conducting channels. Soil is then susceptible to wind and water erosion
- leads to rapid decomposition by increasing micro organism activity
Conservation / no-till impacts
- om increases when no till planters place seeds in narrow band of disturbed soil, leaving rows in between undisturbed.
- residues accumulate
- earth worms increase, creating channels and moving om further down
- effects may vary depending on location and soil depth. In Midwest om may decrease and lower depths. In warmer locations, om has been observed to increase from no till
Crop rotations and organic matter
Om tends to increase with perennial legumes, grasses and legume grass forage crops
High amount of root production of hay and pasture crops, plus the lack of soil disturbance, causes om to accumulate in the soil.
Different crops leave different residues
- corn leaves more than soybeans, wheat, potatoes or lettuce harvests
Harvesting crops in different ways can impact residues
Erosion and om conservation is improved when rotation / sod crops (grass or legume hay) are grown year-round due to soil cover, extensive root systems and decreased decomposition
Synthetic nitrogen and organic matter
Use of synthetic nitrogen can increase growth and thus om, but over application can cause higher rates of decomposition by organisms and lower om
Low organic matter leads to…
Problems with fertility, water availability, compaction, erosion, parasites, diseases and insects become more common. This leads to higher requirements in inputs including fertilizers, irrigation water, pesticides and machinery.
Humus and its particle size
Large surface area to volume ratio means that humus is in contact with a considerable portion of the soil. The intimate contact of humus with the rest of the soil allows many reactions, such as the release of available nutrients to the soil water, to occur rapidly.
Eighteen elements needed by plants
C, H, O, N, P, K, S, Ca, Mg, Fe, Mn, B, Zn, Mo, Ni, Cu, Co, and Ch
C and O (CO2) come from the air, the rest from the soil
Types and balance of organic matter
Living, dead (active) and very dead (humus)
Living - micro organisms
Dead (active) - decomposition leads to nutrient availability and and aggregating glues
Very dead (humus) -
Dynamics of om build up (reverse for degradation)
- Free mineral surfaces that are available for for forming bonds with om will form organic-mineral bonds.
- Larger aggregates will form, made up of smaller aggregates, held together by mycorrhizae fungi and small roots
- Finally om accumulates as free particles (POM) and reaches equilibrium. POM decomposed more rapidly because it is not protected.
Note
- compaction decreases the number of medium to large pores, which reduce the volume of soil available for air, water and organism populations (ie mites and springtails)
- appropriate om amounts vary with soil. There is no set parameters, but you might say 2% for sandy is good, but considered degraded for clay. Want to promote water stable aggregates
- hard to both build up and measure.
- more difficult to build up on course sands that are well aerated, because the potential for aggregation is limited, as are the fine materials that form protective bonds with organic matter
- soils at bottom of hills generally have more om due to run off
Types of vegetation and organic matter
Soils formed under grassland vegetation generally contain more om and a deeper distribution than those under forest vegetation, due to deep and extensive root system with high turnover rates of grassland species. Also slow burning fires from lightening strikes add in biochar that is resistant to degradation
In forestland, high om on top but very low in subsurface (50% goes down to 2%)
Types of organisms
Primary - use fresh residues as their primary source of food. Break down large pieces into smaller fragments
Secondary - feed on primary consumers and their waste
Tertiary - feed on secondary consumers
Can also think of them as very small, small, medium, large, very large
Microorganisms
Very small, primary
Much more in topsoil than subsoil, especially near plants’ rhizosphere
Can fix nitrogen, detoxify, surprise disease organisms and produce products that stimulate plant growth
Source of most antibiotic medicines
Includes: bacteria, fungi, algae and protozoa
Bacteria
Found in nearly every habitat in earth
Most prefer well aerated, neutral ph soils
Among very first to start decomposing residues
Increases availability of nutrients to plants
- dissolve P
- nitrogen fixation (nodules in rhizosphere of legumes
Actinomycetes (sometimes grouped by themselves next to bacteria and fungi) break down lignin, a large complex molecule found in plants
Fungi
Needs oxygen, can tolerate higher acidity in soils
Softens organic debris and makes it easier for other organisms to join the decomposition process
Main decomposers of lignin
Hyphae of mycorrhizal fungi extends out (hyphae) from plant roots to aid in water and nutrient absorption. Hyphae helps to develop and stabilize larger soil aggregates by secreting sticky gel that glues mineral and organic particles together
Protozoa
Single called animals
Primarily secondary consumers
Through grazing on nitrogen rich organisms, they are believed to be responsible for mineralizing (releasing nutrients from organic molecules) nitrogen
Small and medium size soil animals
Includes nematodes, earthworms and insects / others
Nematodes
Simple multicellular soil animals that resemble earthworms
Live in water films around soil aggregates
Many are known as pests and can feed on roots, which can then become entry point for damaging fungi Pythium and Fusarium, as well as vector diseases themselves.
Many are beneficial, fixing nitrogen (can be responsible for 50% of mineralized N) from feeding on fungi, bacteria and other nematodes. Some can parasitize and kill insects such as larvae of cabbage looper and Japanese beetle
Earthworms
Very important - keepers and restorers of soil fertility
Like well aerated soil with an abundance of OM
Various types include night crawler, field (garden) worm, and manure worm. Their activities can vary but generally include the following
fragment and mix fresh residues with soil mineral particles, bacteria and enzymes in their digestive system, resulting in worm casts.
Worm casts are generally higher in plant nutrients, such as N, P, Ca and Mg, than in surrounding soil
Bring food down into their burrows, thus mixing OM deep into soil. Bring soil up to the surface from below. (Natures plow)
Those feeding on debris below the surface contribute to decomposition and mixing
Burrows/channels help with water infiltration, aeration, root growth, loosening compact soil
Can partially control certain diseases and insects, such as apple scab fungus and leaf miner insects
Insects and others
Insects - termites, springtails, ants, fly larvae and beetles.
Others - millipedes, centipedes, mites, slugs, snails, and spiders
Secondary and tertiary consumers, can contribute to decomposition and maintaining balance in ecosystem
Very large soil animals
Includes moles, rabbits, woodchucks, snakes, prairie dogs, and badgers, among others
Often considered a nuisance
Burrows may help conduct water and decrease erosion.
Crawfish, abundant in many somewhat poorly drained soils, in the South help with soil structure
