Introduction to Land Evaluation Basic Soil Science AFNR-BAS-6: Describe soil formation and management and assess its relevance to plant/animal production and natural resources management.

Land Factors  There are seven land factors that are evaluated to determine the best use for an area of land.  Each factor must be evaluated based on criteria for that characteristic. 2

Land Factors  Slope: the steepness of the area or field  Topsoil Thickness: the surface layer of the land measured from the top (ground level) down to the point of change (the beginning of the subsoil)  Erosion: a percentage of the original topsoil which has suffered the harmful effects of water and wind 3

Land Factors  Topsoil Texture: determined by the proportion of sand, silt, and clay in the topsoil (NOT the size of the sand particles)  Permeability of Subsoil: the ability of air and water to move through the subsoil  Drainage: the process of excess water being removed from the soil  Effective Depth: the depth to which plant roots can easily penetrate 4

Finding the Slope  Slope refers to the steepness of an area.  It is determined by estimating the number of feet the land rises or falls over 100 feet and expressed as a percent.  In other words, it is the change in vertical elevation over a given horizontal distance.  You can visually estimate slope by standing perpendicular to the stakes and sighting down your arm. 5

Finding the Slope  To calculate slope, divide the amount of vertical change in elevation by the horizontal distance the change takes place over.  Multiply that number by 100 to get a percentage.  For example, if elevation changes 8 feet over a distance of 50 feet, then: 8 ft. / 50 ft. x 100% =16% slope.  Also if the ground falls 12 feet over a distance of 100 feet then the slope is 12%. (12/100 x 100%) 6

Categories of Slope The category of slope will depend on your state and what area of the state you are in. Often slope is the main limiting factor for the land class of an area. 7

Categories of Slope For Georgia, the categories are as follows. ◦ Nearly Level: 0-2% ◦ Very Gently: 2-6% N. GA, 2-5% S. GA ◦ Gentle: 6-10% N. GA, 5-8% S. GA ◦ Sloping: 10-15% N. GA, 8-12% S. GA ◦ Strongly Sloping: 15-25% N. GA, 12-17% S. GA ◦ Steep : 25-60% N. GA, over 17% S. GA ◦ Very Steep: over 60% N. GA, n/a for S. GA 8

Topsoil Thickness Topsoil is the surface layer measured down to the point of change or the beginning of the subsoil. ◦ Extremely Thick: at least 40 inches ◦ Very Thick: 20 to 40 inches ◦ Thick: 10 to 20 inches ◦ Moderately Thick: 5 to 10 inches ◦ Thin: less than 5 inches 9

Erosion Erosion is percentage of difference between the original topsoil and amount remaining. (amount lost/original thickness) x 100 ◦ None to Slight: less than 25% of the original topsoil lost ◦ Moderate: 25% to 75% of original topsoil lost 10

Texture Topsoil Texture is determined by the proportion of sand, silt and clay. ◦ Fine means that the soil contains at least 35% clay. (feels like heavy flour) ◦ Medium is between Coarse and Fine. (feels like four and salt mixture) ◦ Coarse means that at least 70% of the soil is sand. (feels like salt) 11

Permeability Permeability is the rate of movement of water or air through the soil. ◦ Rapid: a sandy subsoil generally ◦ Moderate: medium-textured subsoil or a sandy clay subsoil that has bright red or yellow colors ◦ Slow: gray or gray mottled, fine, sticky, clay subsoil 12

Drainage Drainage refers to the surface and internal drainage and determines how quickly soil can be tilled following a good rainfall. ◦ Excessive: coarse, sandy materials, over 40 inches deep. ◦ Well-drained: no gray mottles in top 30 inches of soil profile ◦ Moderate: no gray mottles in top 20 inches, but present in inch zone ◦ Somewhat poor: gray mottles in top 20 inches. ◦ Poorly drained: soil is usually gray to surface; subsoil is always predominately gray. ◦ Wet: surface water present 13

Effective Depth Effective Depth is the depth to which plant roots can easily penetrate. ◦ Deep: at least 40 inches ◦ Moderately Deep: at least 20, but less than 40 inches ◦ Shallow: at least 10, but less than 20 inches ◦ Very Shallow: less than 10 inches 14

Land Capability Classes What are land capability classes? ◦ a system designed for classifying land according to its best use ◦ groups fields or areas with similar hazards/limitations 15

Land Capability Classes What are land capability classes? ◦ a system designed for classifying land according to its best use ◦ it groups fields or areas with similar hazards/limitations There are eight classes that have the same meaning in all parts of the U.S. (designated by Roman numerals) the higher the class number, the less the land is suitable for crop production (a.k.a. cultivation) 16

Land Capability Classes can be divided into two broad groups: ◦ land suited for crop production (Classes I, II, III, and IV) ◦ land suited only for permanent vegetation as pasture or forest (Classes V, VI, VII, and VIII) 17

Class I very good land with ideal soils; no limitations restricting it so it can be used for cultivated crop production Characteristics: ◦ Slope: level or very nearly level ◦ Topsoil Thickness: thick or moderately thick ◦ Erosion: none to slight ◦ Texture: coarse or medium ◦ Permeability: moderate ◦ Drainage: well drained and not subject to overflow ◦ Effective Depth: deep 18

Class II have some limitations that require moderate conservation practices but suitable for crop production Characteristics: ◦ Slope: nearly level or very gently sloping ◦ Topsoil Thickness: very thick, thick, moderately thick, or thin ◦ Erosion: slight or moderate ◦ Texture: coarse, medium, or fine ◦ Permeability: moderate or slow ◦ Drainage: well drained or moderately well drained ◦ Effective Depth: deep or moderately deep 19

Class III may be used for crop production if certain conservation practices are followed; choice of crops is reduced due to limitations Characteristics: ◦ Slope: nearly level, very gently sloping, or gently sloping ◦ Topsoil Thickness: extremely thick, very thick, thick, moderately thick, or thin ◦ Erosion: slight, moderate, or severe ◦ Texture: coarse, medium, or fine ◦ Permeability: moderate or slow ◦ Drainage: well drained, moderately well drained, somewhat poorly drained ◦ Effective Depth: deep, moderately deep, or shallow 20

Class IV borderline cultivatable land; may be used for crop production if carefully managed; severe limitations that restrict crop choice and should be on a rotational basis Characteristics: ◦ Slope: nearly level, very gently sloping, or sloping ◦ Topsoil Thickness: extremely thick, very thick, thick, moderately thick, or thin ◦ Erosion: slight, moderate, or severe ◦ Texture: coarse, medium, or fine ◦ Permeability: slow, moderate, or rapid ◦ Drainage: excessively drained, well drained, moderately well drained, somewhat poorly drained, or poorly drained ◦ Effective Depth: deep, moderately deep, shallow, or very shallow 21

Class V these soils are very wet but may be used for pasture usually found in small and nearly level drainageways not subject to erosion but do have drainage problems and frequent flooding the degree of wetness limits their use unfit for cultivation Characteristics: ◦ Slope: nearly level or very gently sloping ◦ Topsoil Thickness: moderately thick to thick ◦ Erosion: none to slight ◦ Texture: coarse or medium ◦ Permeability: slow ◦ Drainage: poorly drained to wet ◦ Effective Depth: deep to shallow 22

Class VI these soils unfit for cultivation and their severe limitations restrict use to pastures and forestry hazards include steep slopes, erosion, or shallow soils Characteristics: ◦ Slope: strongly sloping ◦ Erosion: severe ◦ Effective Depth: shallow 23

Class VII not suitable for crop production and has severe limitations for pasture or forestry use requires extensive management of conservation practices to control erosion major hazards are severe erosion and/or slope Characteristics: ◦ Slope: steep or very steep 24

Class VIII only suited for wildlife or recreation purposes Characteristics: ◦ usually extremely stony, sandy, or wet 25

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