Soils

Soils

•Definition of soil

–Soil is the portion of earth's crust that has formed form the decomposition of rocks and minerals through physical, chemical and biotic forces.

Soil Composition

•The composition of garden soil

–Mineral matter (sand, silt and clay)

–Microbes (bacteria, fungi, and algae)

–Animals (worms, insects, snakes, mammals)

–Organic matter (decaying matter that was once alive; plants, animals and microbes)

–Pore space (open spaces occupied by air or water)

Soil formation

•Soil is derived from parent rock, minerals and decaying organic matter.

•2 major processes in soil formation

–1. accumulation – parent material accumulation from breakdown of parent rock by weathering.

–2. differentiation – is mechanical separation and/or dissolution of parent material

Soil Horizons

•Soil horizons are individual layers seen by exposing a vertical cross section of soil.

•A horizon – living layer, often called topsoil

–It is dark due to organic matter.

–Coarsest, most fertile, most root

•B horizon – second layer often called subsoil

–Made of more compacted material

–Contains finer particles

–Brighter in color

–Often nutrient rich

–Low in organic matter

–Stores water

•C and R horizon – parent soil material and rock

Soil formation

•Soil is a natural product of the environment.

•Native soil form from the parent material by action of climate (temp, wind and water), native vegetation and microbes.

•Shape of land surface,

Soil Characteristics

•Soil texture and soil structure

Soil Color

•Soil color can be darker due to o.m.

•Soil profile changes in color from surface to subsoil.

Soil texture

•Soil texture is the relative volume of sand, silt and clay particles in a soil.

•Soil texture affects the water-holding capacity of soil, movement of water through the soil and ease of cultivation.

1. particle size

sand - visible

silt – size of talc

clay - microscopic

–2. Textural classes –

•Sand is largest particle.

•Sandy soils are coarse textured.

•Fine textured soils are mostly clay o clay and silt.

•The same weight of clay can hold 50 times as much water as very fine sand particles.

•Soils with high percentage of clay are undesirable because he small particles pack tightly together, leaving little pore space for air and water; digging would be difficult.

•Clay particle tightly bind nutrients.

•Loam is ideal garden soil; mixture of sand, clay and silt.

•Soil texture is important because it affects how easily soil can be worked, how well it hold water.

–Ie. Coarse textured or sandy soils, allow water to enter and pass through more quickly.

–Ie. Sandy soils can be tilled more easily, dry more quickly and are not rich in nutrients.

Soil Structure

•Soil structure results from the binding together of soil particles into aggregates or clumps of varying sizes and shapes.

•Aggregates can be small as a grain of sand or as large as a pea.

•A well-structured soil is made up of aggregates of varying sizes that allow maximum space for air and water.

•These aggregates form as a result of physical forces: wetting and drying cycles.

•Organic matter promotes stabilization of the aggregate particles. Decaying organic matter acts like a glue to hold soil particles together.

•Unnecessary digging or rototilling may break down aggregates into a fine powder, reducing pore space.

Air and Water Movement

•Soil structure is critical to plant health because it affects root development.

•Soil structure is more important than texture, color or parent material.

•Good soil structure allows water and air movement and it provides channels through which roots grow.

•Overworked, poor soils show a very indistinct soil structure. Aggregates do not exist, few air spaces.

•Roots can suffocate and die where large amounts of water have forced air out of the space.

•Tilth is ter used to describe how easily soil can be tilled.

•Soil with good tilth allows seedlings to emerge easily.

•It allows roots to penetrate soil. Soil wit good tilth has good structure.

Biological impact

•Living organisms impact soil structure.

•O.M. attracts earthworms that drill channels deep into the subsoil. Channels provide needed space for plant roots, air and water.

•Castings left behind improve nutrient level

•Microbes live in soil.

•Microbes digest some nutrients and o.m. into simpler units that plants use.

•Organic remains of microbes improve soil structure.

Improving soil structre

•Addition of o.m. and working the soil at the proper moisture level .

•Working the soil wet compacts structure and reduces air and water spaces.

Drainage

•Drainage is the rate ad amount of water movement through and across soil.

•Water is solvent for the for plant nutrients

•etc

Soil pH

•The pH scale is a measure of the degree of acidity or alkalinity

•The pH scale has 14 divisions ranging from 1 to 14.

•The pH 7 is neutral.

•Acid soils 1 to 6.9 called sour.

•Alkaline soils 7.1 to 14

•The pH of soil affects the availability of plant nutrients.

•Nutrients become less available at pH extremes.

•Azalea, rhododendron, holly, blueberry do well in acid soils

Correct pH

•Commercial fertilizer can cause soil to become acid.

•Lime cause to soil to become more alkaline. Lime is safe to use, nontoxic to humans and does not cause pollution problems.

•Dolomite lime offers the added benefit of magnesium.

•Add sulfur to lower pH.

•Chelated iron sulfate or aluminum sulfate has an acid reaction and is used correct chlorosis or yellowing of leaves.

•Overly alkaline soil interferes with plant uptake or iron. Iron sulfate reduces alkalinity and adds iron.

Soil Modifications

•Mechanical

–Mechanical modification is merely a means of improving soil structure by digging (shovel, spade, garden fork or rototiller).

–Compaction reduces pore space in soil.

–Improper digging or tilling can compact soil

–Digging or walking on wet soils causes compaction.

Amendments

•Another way to improve the quality of soil is by the addition of various amendments such as fertilizer, peat moss, compost, manures, worms, inoculants, sharp sand, lime, green manures or cover crops, mulches and sewage.

•Humus, peat moss, sludge, manures and cover crop will increase water-holding capacity of sandy soil by increasing surface area to which moisture can cling. Can also improve soil structure.

•Fertilizers, sludge, manures and green manures add some nutrients

•Lime and sulfur adjust pH

Composting

•Humus is valuable soil amendment.

•Composing is the production of humus from selected garden and kitchen wastes.

•Microbes break down organic raw materials into humus.

•Humus is organic matter in a form plants can use.

•It adds small amounts of nutrients.

•Humus improves soil structure, water-holding capacity and nutrient-holding capacity.

•Diverts yard waste from landfills

•Unprocessed organic matter such as fresh grass clippings, garden debris, leaves, sawdust and wood chips is not as good as humus.

•Microbes use nitrogen in the process of breaking down this organic matter.

•Decomposition depletes nitrogen, nitrogen should be added where large amounts of unprocessed organic matter are used.

Benefits of adding humus to soil

•Scientific studies show fruits and vegetables gown in humus have higher sugar content.

•Humus improves the structure of soil, preventing a hard crust from forming on the surface. Germinating seedlings can easily push through and roots can easily grow.

•Humus attracts earthworms that burrow up from nutrient-rich subsoil depositing nutrients in the topsoil layer.

•Organic soils warm up faster.

Pile type composting

•A pile minimum of one cubic yard is needed.

•Ideal ratio of dry (brown) organic mater to wet (green) organic matter should be 30 to 1. eg 30 parts dry leaves to 1 part grass clippings.

•Dry organic material

–Newspaper/paper

–Hay or straw

–Branches, ever green needles

–Sawdust

–Dried leaves

Wet organic material

•Any green plant materials

•Nongreasy kitchen scraps (eggshells, vegetable and fruit scraps)

•Manure (no cat, dog or human feces)

•Composting methods that produce high temperatures (140 degrees F) will kill weed seeds and disease organisms and break down most pesticides on plant material.

•Plant material treated with insecticides, miticides or herbicides should be composted for a minimum of 6 months.

•Smaller pieces of matter decompose more quickly.

•Air space and water are both essential for decay.

•Layers should be loose and moist.

•Moisture should be like wrung-out sponge.

•Adding a few shovelfuls of garden soil and turning the compost promotes faster decomposition.

•Addition of fertilizer containing nitrogen speeds decay. It adds to the nutrient value of the finished product.

Green Manures

•Green manures or cover crops are a means of protecting and improving soil quality.

•Eg. Plant crop and plow under.

•Value of green manure:

–Provides organic matter

–Holds nutrients that ma be lost.

–Reduces erosion and loss of topsoil

–Legume cover crops can increase amount of nitrogen in soil

–Deep-rooted cover crop allowed to grow for season greatly improves the soil tilth.