CRSS 2830 Lesson 6: Basic Soils

I. SOIL DEFINED “That portion of the Earth’s crust that is made up of mineral materials, organic matter (living and dead), water, and air that is capable of supporting plant growth.”“That portion of the Earth’s crust that is made up of mineral materials, organic matter (living and dead), water, and air that is capable of supporting plant growth.”

SOIL DEFINED Takes about a 1000 yearsTakes about a 1000 years for a 6-inch soil layer to form for a 6-inch soil layer to form

II. SOIL TEXTURE Mineral portion of soil is made up of three particle sizes: sand, silt and clayMineral portion of soil is made up of three particle sizes: sand, silt and clay

SOIL TEXTURE CHARTS AND GRAPHS

III. SOIL STRUCTURE Arrangement of the mineral particles into secondary units or aggregates. Like crumbs of a cake.Arrangement of the mineral particles into secondary units or aggregates. Like crumbs of a cake. Size and arrangement of aggregates, influence pore space.Size and arrangement of aggregates, influence pore space.

IV. AIR Air fills the soil pore space not filled with water.Air fills the soil pore space not filled with water. Oxygen is needed by roots for water and nutrient uptake. Stay above 10 to 12 %Oxygen is needed by roots for water and nutrient uptake. Stay above 10 to 12 %

AIR Water logged or compacted soils can result in both limited oxygen and elevated carbon dioxideWater logged or compacted soils can result in both limited oxygen and elevated carbon dioxide Carbon dioxide at high levels will impede root growth above 5%Carbon dioxide at high levels will impede root growth above 5%

V. WATER In between solids, soils contain pores that are filled with air or water.(total porosity).In between solids, soils contain pores that are filled with air or water.(total porosity). Total porosity: sand = %, clay = %. Which drains faster? Why?Total porosity: sand = %, clay = %. Which drains faster? Why?

WATER Pores differ in size. Macropores, “large” and micropores “small”. Air fills macropores, water fills micropores. (mesopores fall between in size). Ideally want soil at 50% air and 50% water.Pores differ in size. Macropores, “large” and micropores “small”. Air fills macropores, water fills micropores. (mesopores fall between in size). Ideally want soil at 50% air and 50% water.

VI. ORGANIC MATTER Living: earthworms, gophers, insects, mice, millipedes, mites, nematodes, fungi, bacteria, etc. Important for breakdown of organic matter to humus and nutrient release/cycling.Living: earthworms, gophers, insects, mice, millipedes, mites, nematodes, fungi, bacteria, etc. Important for breakdown of organic matter to humus and nutrient release/cycling.

ORGANIC MATTER Nonliving: dead plant and animal residues break down to humus. Humus has negative charge which can help adsorb many plant nutrients.Nonliving: dead plant and animal residues break down to humus. Humus has negative charge which can help adsorb many plant nutrients.

VII.CHEMICAL PROPERTIES OF SOILS Plants are:Plants are: –75 to 85 percent water –15 to 25 percent dry matter

CHEMICAL PROPERTIES OF SOILS Carbon, hydrogen and oxygen come from air and water. The remaining 13 come from the soil.Carbon, hydrogen and oxygen come from air and water. The remaining 13 come from the soil. The dry matter is made up of 16 essential elementsThe dry matter is made up of 16 essential elements

CHEMICAL PROPERTIES OF SOILS Some of the nutrients have a positive chargeSome of the nutrients have a positive charge (cations) (cations) Some have a negative chargeSome have a negative charge (anions) (anions)

CHEMICAL PROPERTIES OF SOILS charges. Therefore, the positive charges. Therefore, the positive (cations) are attracted. (cations) are attracted. Cation Exchange Capacity (CEC) = Ability of soil to absorb exchangeable cations.Cation Exchange Capacity (CEC) = Ability of soil to absorb exchangeable cations. Clay soils and organic matter have negative Clay soils and organic matter have negative

VIII. SOIL REACTION (pH) pH scale measures acidity or alkalinity:pH scale measures acidity or alkalinity: –Below 7.0 is acid –Above 7.0 is alkaline –7.0 is neutral

SOIL REACTION pH of 6.0 to 7.0 is best for turfgrass growthpH of 6.0 to 7.0 is best for turfgrass growth 6.0 to 7.0 is the pH range in which the essential nutrients are in available form.6.0 to 7.0 is the pH range in which the essential nutrients are in available form.