Soils Part One

Question 1

In addressing soil problems, you are trying to…

Answer 1

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

Question 2

Soil consists of…

Answer 2

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

Question 3

Soil texture and organic matter

Answer 3

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.

Question 4

Soil erosion and Organic Matter

Answer 4

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

Question 5

Soil compaction, aggregates and organic matter

Answer 5

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

Question 6

Large pore formation and benefit

Answer 6

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

Question 7

PH balance and organic matter

Answer 7

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

Question 8

Soil color and organic matter

Answer 8

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).

Question 9

Nitrogen and organic matter

Answer 9

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

Question 10

Weather/climate and organic matter

Answer 10

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.

Question 11

Nutrients and organic matter

Answer 11

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

Question 12

Tillage and organic matter

Answer 12

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

Question 13

Crop rotations and organic matter

Answer 13

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

Question 14

Synthetic nitrogen and organic matter

Answer 14

Use of synthetic nitrogen can increase growth and thus om, but over application can cause higher rates of decomposition by organisms and lower om

Question 15

Low organic matter leads to…

Answer 15

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.

Question 16

Humus and its particle size

Answer 16

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.

Question 17

Eighteen elements needed by plants

Answer 17

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

Question 18

Types and balance of organic matter

Answer 18

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)

1. Free mineral surfaces that are available for for forming bonds with om will form organic-mineral bonds.
2. Larger aggregates will form, made up of smaller aggregates, held together by mycorrhizae fungi and small roots
3. 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

Question 19

Types of vegetation and organic matter

Answer 19

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%)

Question 20

Types of organisms

Answer 20

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

Question 21

Microorganisms

Answer 21

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

Question 22

Bacteria

Answer 22

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

Question 23

Fungi

Answer 23

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

Question 24

Protozoa

Answer 24

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

Question 25

Small and medium size soil animals

Answer 25

Includes nematodes, earthworms and insects / others

Question 26

Nematodes

Answer 26

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

Question 27

Earthworms

Answer 27

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

Question 28

Insects and others

Answer 28

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

Question 29

Very large soil animals

Answer 29

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