Soils and Cultivation

Soils are defined as the loose surface of the earth, or that material which nourishes and supports growing plant, or the material which supports foundations, roads, etc. But common sense tells us that soils are the solid medium in which plants grow.

Functions of Soils

Plant support Supplies H2O, Oxygen Supplies Nutrients Protection from stresses Magic -symbiotic

relationships -unknown chemicals/substances

Chemical Composition of Earth’s Crust

Element % by WeightOxygen 47Silicon 28Aluminum 8.1Iron 5.8Calcium 3.6Sodium 2.8Potassium 2.6Magnesium 2.1

Where Do Soils Come From?

Parent Rock breaks down into smaller rocks, then gravel, then further into sand sized particles. Sand is further broken down into silt sized particles. To this point, it is mainly a matter of subdividing the original parent rock. This means that the chemical composition of sand and silt is very similar to the parent rock.

Where Do Soils Come From?

Clay, on the other hand, is very different. In addition to being much smaller than the other particles, it has unique structures, and is unlike the parent rock material. Clay has a very large surface area; surfaces are where things happen in a soil. Clay is chemically very reactive, and dominates the soil in terms of its effect on soil processes.

Where Do Soils Come From?

Weathering is the process that converts parent rock material into a soil. It is a very long term process. Several different components contribute to weathering, including the type of parent material, climate (temperature, rainfall, freeze/thaw cycles), plants, and microorganisms.

Soil Components

Solids - sand, silt and clay, organic matter

Pore spaces - water-filled

air-filled

Solids

Water

Air

Balance of Aeration and Moisture

SolidWater

Air

Solid

Solid

Water

Water

Air

Air

Ideal balance Waterlogged soil

Compacted soil

Characteristics of Soils

Physical Properties Chemical Properties (Nutrition) Reactivity (pH) Organic Matter Biological Activity

Physical Properties:Soil Separates

Separate Diameter, mm Surface area cm

2/Gram

V. Coarse Sand 1.00 - 2.00 11Coarse Sand 0.50 - 1.00 23Medium Sand 0.25 - 0.50 45Fine Sand 0.10 - 0.25 91V. Fine Sand 0.05 - 0.10 227Silt 0.002 - 0.05 454Clay less than 0.002 8,000,000

Soil Class

Soils are usually composed of several or many “separates”. The proportions of the component separates determines the soil class. For example, a soil might contain 20% clay, 40% silt and 40% sand. This mixture is classified as a loam, based on the soil textural triangle. Soil texture is very important, but so is soil structure.

Soil TexturalTriangle

Soil Structure

How the soil particles are arranged and associated with each other is called soil structure. Individual particles aggregate together, glued by attractive forces and by microbial activity plus organic matter. Soil structure can improve a poor soil texture.

Soil Porosity

Pores exist between individual soil particles. These may be either large (macropores) or small (micropores), which is largely determined by the size of the individual particles and aggregates. Pores size is important because it determines permeability and percolation rate.

Fine textured soils,lots of micropores,some macropores

Coarse textured soils,mainly macropores

Soil Percolation, Infiltration

Percolation is how quickly water moves through a soil

Infiltration is how quickly water moves into a soil from the surface

Both depend on pore structure. Both are important considerations in water management and drainage design.

Soil Porosity

Macropores are large enough to drain after being filled with water from rain or irrigation. Air enters after water drains, which is very important for root health.

Micropores are small enough to hold water against the downward force of gravity. This water is what the plant uses.

Soil Aeration

Soil aeration is one of the most important factors affecting turf health. Poor aeration can lead to root death. The black layer often found in putting greens is due to poor aeration.

You can improve aeration by encouraging good soil structure and by cultivation.

Soil Compaction

Soil compaction occurs when forces, such as tire or foot traffic, compress the soil and alter pore structure. Bulk density increases, macropores decrease, infiltration decreases, aeration decreases. Compaction is most a problem when soils are wet. A similar problem is caused by shearing forces or puddling of soil surfaces.

Soil Compaction Soil compaction is controlled by restricting

traffic, modifying soils, and cultivation. Soils can be modified to resist compaction,

but it’s not as simple as it sounds. The old dogma about adding a little sand to lighten a heavy soil is just plain wrong. But pure sands are great for resisting compaction.

Cultivation is practiced in many forms.

Soil Cultivation

Cultivation before planting is pretty easy, as long as the soil is not too wet.

Cultivation after planting is the basis of an entire equipment industry. Pieces include hollow and solid tine aerifiers, water injectors, air injectors, slicers, spikers, wing blades, and Klingon disruptor beams.

Ryan Core Aerifier

Rotating Hollow Tines

Soil Cores

Soil Cultivation What does cultivation do? The idea is to

increase the surface area or increase the macropore space to facilitate infiltration and percolation, and to increase air diffusion into the soil. Core cultivation, especially solid tine, can create compaction around the holes. A plow layer can occur when same tine depth is always used.

Soil Cation Exchange Capacity

CEC is a measure of how negatively charged a soil is, and is related to clay content. Sands have very low CEC’s, silts somewhat higher, but clays usually have very high CEC’s. Cation exchange sites occur at the surface of a soil particle, and are negatively charged. They attract cations, such as NH4, K, Ca, Mg, etc.

Soil Cation Exchange Capacity

CEC is important because it represents a reservoir of some nutrients for the plant. Cations stick fairly tightly to the sites, but on occasion come off and go into solution in the soil water. These cations can then be absorbed by the plant roots.

Cation Exchange

Clay particle

K+

K+

K+

K+

K+

K+

K+

K+

K+

Ca++

Ca++

Ca++

Mg++

Mg++

NH4+

NH4+

NH4+

_ _ _ ____

___

__

__

__ _ ___ _

_

Cation Exchange

Clay particle

K+ K+

K+

K+

K+

K+

K+K+

K+

Ca++

Ca++

Ca++

Mg++

Mg++

NH4+

NH4+

NH4+

_ _ _ ____

___

__

__

__ _ ___ _

_

Soil Reactivity

Soil reactivity is a measure of how acid a soil is, or soil pH. Soil pH affects root function and nutrient availability, and must be monitored by the turf manager.

Most soils have pH’s between 5 and 9, with somewhere around 6.5 being ideal for most grasses.

Many of our soils are quite acid. Why?

Soil pH

Many of our soils are highly weathered. This means that most of the basic cations (K, and especially Ca and Mg) have been washed out of the soil. They are replaced by protons (H), which are the basic unit of acidity.

This contrasts to younger soils, which are less weathered and more neutral.

Cation Exchange, Acidic Soils

Clay particle

K+

K+

K+

K+

K+

H+

NH4+

NH4+

NH4+

_ _ _ ____

___

__

__

__ _ ___ _

_

H+

H+

H+

H+

H+H+

H+

H+

H+

H+

Cation Exchange, Acidic Soils

Clay particle

K+

K+

K+

K+

K+

H+

NH4+

NH4+

NH4+

_ _ _ ____

___

__

__

__ _ ___ _

_

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

Soil pH How do we control soil pH? If the soil is acid, we need to raise the pH

towards neutral. The most common way is to lime the soil. Lime is calcium carbonate, or calcium plus magnesium carbonate. The amount required will depend on the soil, and should be determined by a soil analysis.

Lime granule size is important also.

Soil pH

Lime can be applied either preplant (high rates can be used all at once) or to a mature turf. But then, lower rates are necessary. Do not apply more than 40-50 pounds of lime per thousand square feet to an existing turf. Water in after application. Several to many applications may be required.

Soil Nutrients

C, H, O, from the air, water The rest from the soil C HOPKNS CaFe ClZn, MoB CuMn

Mg See Hopkins Cafe Closin’, Mob Comin’

with Machine Guns

Soil Nutrients

Many nutrients are in adequate supply in the soil, and do not need to be added

Some are readily lost from the soil, or are present but not available. These need to be added as fertilizer. N, P, sometimes K, Fe, rarely S.

Soil Nutrients The only way to tell if your soil has special

needs, or even routine needs, is by a soil test using a reputable lab. Home chemistry kits are not usually practical or accurate.

Samples should represent an entire use area. Collect 12 or more cores, 4-6”deep and mix them together. A total of about a quart is usually more than enough for the lab.