Soils and Growing Media 5.02 Discuss the soil profile and soil sampling for surface and subsurface layers

Soil Profile Layers of soil are called horizons: O Horizon – Organic Matter (2”) A Horizon – Topsoil (4”) (most fertile, most organic matter, top or first layer). Most smaller plants and grasses only grow in top 6” of soil. B Horizon - Subsoil. C Horizon - Parent Material R Horizon - Bed rock

Soil Profile All soil profiles do not have the same number or level of horizons For example, a sandy soil may not have an “O” horizon if it has been under cultivation Other soils may have a horizon missing due to erosion. Most typical soils in NC will have a minimum of the A, B, and C or R horizons

Soil Profile O horizon Rich soil found where a plant cover has been in place for an extended time Rich in organic matter in various stages of decomposition and is dark in color It is the most fertile layer in the soil profile

Soil Profile A Horizon Is the topsoil and most fertile in the absence of an O horizon A horizon lies just below the O horizon and is home to earthworms and soil organisms Brown in color due to organic matter in the soil

Soil Profile B Horizon The subsoil Clayey soil that has high mineral content Usually brown or reddish due to the large amount of clay

Soil Profile C Horizon R Horizon Parent Material Consists mainly of clumps of un-weathered rocks R Horizon Bed rock Cannot be dug by hand and very few roots can penetrate the bedrock

Soil Horizons

Soil Structure How particles cluster together. Sandy soils have loose structure Silty soils have granular Clayey has blocky or platy Granular is best. Plants have good root development Water movement is at an appropriate rate Doesn’t stay too wet or too dry

Soil Texture = Size of Particles Sand Clay Silt

Sand Large particles, low moisture and nutrient holding capacity.

Silt Medium sized particles and good moisture and nutrient holding capacity.

Clay Small particles Has high water and nutrient holding capacity.

Loam Loam has almost equal parts of sand, silt, and clay This is the ideal texture for most non-container outside plants

Soil pH Measures the acidity or alkalinity of soils Ranges from 0-14. 0-6.9 is considered an acid soil, 7 indicates a neutral soil, and 8-14 is considered alkaline Lime will raise the pH value (make it less acidic) Calcium or sulfur will lower the pH value (make soil more acidic)

pH Ideal pH for most ornamental plants and turf is 5.5 to 7.0 Acid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acid Basic (alkaline) Neutral

Other Soil Properties Permeability is the rate at which water moves through the soil Water holding capacity is the ability of a soil to hold water for plant use Porosity is the amount of air space between soil particles

Other Soil Properties About 50% of soil should be solid particles. 45% mineral matter, 5% organic matter About 50% of soil should be pore space. About 25% of pore space should be filled with water, 25% air space Soil structure is more important to producers who grow plants in natural soils because producers of container grown plants add ingredients to make growing media desirable.

Soil Sampling Is essential for an accurate fertilizer recommendation for growing plants Soil sampling procedures: Create a visual grid of the area to be planted For gardens and landscapes, take 5-10 subsamples from the site to be evaluated Sample before the growing season

Soil Sampling Procedures: Use a stainless steel soil-sampling probe Take the surface sample to tillage depth or about 3-4 inches for lawns, and 6-8 inches for crops Mix the soil samples together

Soil Sampling Remove any grass, rocks or other material besides soil Avoid unusual spots in the lawn or field. Those areas need to be sent in a separate box Place soil samples in a box, which you can obtain form the County Extension Office with Soil sample information sheet Send the box and information to Agronomic Division Soil Test Lab in Raleigh for a free soil test