Soil 50% pores and 50% solids

Sand A soil solid No electrical charge No electrical charge Very large pore spaces Very large pore spaces Water drains rapidly Water drains rapidly

A soil solid Clay A soil solid Retains nutritional elements (due to negative electrical charge) Retains nutritional elements (due to negative electrical charge) Very small pore spaces Very small pore spaces Water drains very slowly Water drains very slowly

(A cation is an atom with a positive charge) 20 MILLION hydrogen atoms laid in a line would equal 1 mm

N +/- P + K + S - Ca + Mg + Fe + Mn + Cu + Zn + B + Mo - Al + Primary nutrients Secondary nutrients Micronutrients {Ni + and Cl - are sometimes included} science.uq.edu.au Most of the nutrients that plants need have a positive electrical charge.

Soil can be thought of as a storehouse for plant nutrients.

SOIL Soil provides all that a plant needs with the exception of…

SOIL CO 2 sunlight

soil does provide: soil does provide: Oxygen Oxygen Water Water Nutrients ( 13-14) (N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,-- Al,Cl,Ni ) Nutrients ( 13-14) (N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,-- Al,Cl,Ni ) – Some sources include aluminum (Al) while others list chlorine (Cl) and nickel (Ni) as micronutrients

Tilth Suitability of a soil to support plant growth {physical condition of a soil}

Tilth Relates to: Structure Structure – Aggregate formation – greater degree of aggregation = better tilth Texture is the percent of: Texture is the percent of: – Clay, Silt and Sand minerals

Aggregates --soil structure-- Soil particles that are held together by Soil particles that are held together by – Sticky organic substances produced by microorganisms and plant roots. (polysaccharides – i.e. sugars) – Enmeshment – fungal hyphae and fine plant roots – Electrostatic forces

Tilling Cultivation: Cultivation: – Breaks apart aggregates – Collapses pores – AVOID TILLING EXCEPT TO: Mix in organic matter Mix in organic matter Control weeds Control weeds Prepare seed beds Prepare seed beds

Oxygen Oxygen Water Water Nutrients (13-14) (N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,-- A l,Cl,Ni ) Nutrients (13-14) (N,P,K,S,Ca,Mg,Fe,Mn,Cu,Zn,B,Mo,-- A l,Cl,Ni ) Better tilth means better access to the essentials for growth

Tilth Suitability of a soil to support plant growth (physical condition of a soil); -moisture retention -drainage-aeration -ease of seed germination and emergence -ease of root development & penetration -ease of tillage -does not directly pertain to nutrition

relative Size of Sand, Silt and Clay Clay below mm - sticky Silt to 0.05 mm - silky Sand 0.05 to 2.0 mm - gritty

The diameter of a clay particle is 1,000 times smaller than the diameter of a large grain of sand or the thickness of a key (the average house key is 2 mm thick). Individual clay particles can only be seen with a microscope.

Relative size of soil particles

Small Pores in clay can prevent plants from getting water ≈ capillary action ≈ In low water conditions, the clay will feel moist but the water is not available for the plants. Under these low water conditions, capillary action results in water being held so tightly to the clay particles that the forces of transpiration cannot overcome the adhesive forces holding the water to the clay.

Transpiration Transpiration is the evaporation of water from plants. It occurs chiefly at the leaves while their stomata are open. Transpiration is the "engine" that pulls water up from the roots to: – supply photosynthesis; – bring minerals from the roots for biosynthesis within the leaf; – cool the leaf.

When there is minimal water present, it will only fill the very small areas between the clay particles. When there is minimal water present, it will only fill the very small areas between the clay particles. Under these conditions, the force of attraction between the soil and water is greater than the forces exerted by transpiration to pull the water into the roots. Under these conditions, the force of attraction between the soil and water is greater than the forces exerted by transpiration to pull the water into the roots. The net result is that the clay feels and looks moist but the water is bound too tightly to be available to the plants. The net result is that the clay feels and looks moist but the water is bound too tightly to be available to the plants. Moist Clay ≠ Happy Plants

Roots can get water as long as they can overcome the adhesive forces that hold water to the soil particles.

…are multi-access highways for: - air - water - soluble nutrients - plant roots - microbes Soil pores…

Medium sand silt Comparing pore spaces in sand to those in silt.

- Medium sand silt Pores enable: - aeration -moisture availability -root growth - aeration -moisture availability -root growth

Adequate Oxygen levels and soil tilth  Plenty of pores for optimum oxygen diffusion  Good drainage to avoid water saturation

Healthy white roots

-- low soil oxygen is the most common limiting factor of plant (root) growth. ~small pores and/or excessive water~

Oxygen is necessary for the normal growth processes of root and plant Oxygen is necessary for the normal growth processes of root and plant Oxygen diffuses through air in soil pores Oxygen diffuses through air in soil pores Oxygen diffuses very slowly through water Oxygen diffuses very slowly through water Oxygen dissolved in water is used up very quickly and new oxygen arrives very slowly by diffusion. Oxygen dissolved in water is used up very quickly and new oxygen arrives very slowly by diffusion.

Root development in self- watering containers Healthy roots in container with adequate water supply. Poorly developed roots due to excessive water. Notice the lack of healthy, white roots.

AMENDMENTS  IMPROVE SOIL TILTH  PROVIDE NUTRIENTS

Loam≈ A type of soil that does not include any organic material!

Loam consists ONLY of minerals (sand, silt and clay)

Sandy loam ≈≈≈ Good soil for a garden is SANDY LOAM TRUE LOAM has too much silt and clay to drain readily and is a poor soil for garden use.

Sandy Loam Good soil for a garden is SANDY LOAM -less silt and clay and more sand than a true loam -sand should be predominately coarse and medium sized particles (i.e. >0.25mm) (i.e. >0.25mm)

Clay soils are usually: Fertile - negative charge so good nutrient retention (storehouse) Fertile - negative charge so good nutrient retention (storehouse) Tend to compact and thus limit O 2 availability Tend to compact and thus limit O 2 availability Inadequate pore space for good air and water movement Inadequate pore space for good air and water movement As little as 20% clay particles result in soil behaving like a clayey, sticky soil. As little as 20% clay particles result in soil behaving like a clayey, sticky soil. Source: Colorado State Extension Service Source: Colorado State Extension Service

SoilTextureTriangle

AMENDMENTS  IMPROVING SOIL TILTH  Water retention --addition of organic material -addition of vermiculite (not perlite) -addition of clay to sandy soil -what about underlying clay soil ?(it will limit drainage)  Pore size  Nutrient retention

VERMICULITE VERMICULITE – Increases moisture holding capacity holding capacity – Increases pore space PERLITE PERLITE – Low water holding capacity – Increases pore space AMENDMENTS

Tilth Suitability of a soil to support plant growth (physical condition of a soil); -moisture retention -drainage-aeration -ease of seed germination and emergence -ease of root development & penetration -ease of tillage

AMENDMENTS  IMPROVING SOIL TILTH  PROVIDING NUTRIENTS  Microbial activity  Microbial activity (see SOIL {2})  Correcting deficiencies  Soil test (LSU – pH, P, K, Ca, Mg, Na, S, Cu and Zn)