3Soil Characteristics Organic Content Mineral Content Soil Texture 3 characteristics of soil that affect its VALUE for farming and growing vegetation are:Organic ContentMineral ContentSoil Texture
4Organic Content organic content (dead and decomposing material) Soil fertility is determined as a ratio of the organic content to the content of ground bed rock.
5Mineral Content Provide nutrients for various plant life. Ex. Potassium, calcium, phosphorous, nitrates etc.Varies with precipitation!Ex. Heavy rains tend to leach soils removing minerals from the root region of soil.
6Soil Texture refers to the mixture of: fine particles (sand), very fine particles (silt) andextra fine particles (clay).The BEST texture for agriculture is an even mixture of each. (referred to as loam)LOAM is a mixture of these particles that provide sufficient space to allow:root penetration,aeration (air flow),nutrient flow anddrainage / water retention.
8Particle Size Differences Different properties based on the size of the particles, even if same mineral.Function of surface area.2 mm2 umLARGESANDCLASTLARGECLAYCLAST4 um2*6 = 24 m24 mm2*6 = 24 mm2Potential surface area withinsand grain volume: 24 x 109 m2Surface area: 24 x 106 m2Note: Most clasts are not square and would not fit together, leaving pore space.
9Triangular graph of Soil Texture 30% sand50% clay20% siltPg. 139
10Using the triangular graph of soil texture, which condition would make the least favourable soil for farming?(A) 40% sand, 20% clay, 40% silt (B) 30% sand, 10% clay, 60% silt(C) 25% sand, 60% clay, 15% silt (D) 50% sand, 10% clay, 40% silt*
11Using the triangular graph of soil texture, which combination would make the poorest soil? A) 20% sand, 70% clay, 10% silt B) 60% sand, 30% clay, 10% siltC) 40% sand, 30% clay, 30% silt D) 50% sand, 10% clay, 40% silt*
12Using the triangular graph of soil texture, a soil texture combination of 20% sand, 10% clay and 70% silt would constitute which soil type? (A) sandy clay (B) sandy loam (C) silty clay (D) silty loam*
13* Using the triangular graph of soil texture, which condition would make the least favourable soil for farming?(A) 40% sand, 20% clay, 40% silt (B) 30% sand, 10% clay, 60% silt(C) 25% sand, 60% clay, 15% silt (D) 50% sand, 10% clay, 40% silt*
14Using the triangular graph of soil texture, which combination would make the poorest soil? A) 20% sand, 70% clay, 10% silt B) 60% sand, 30% clay, 10% siltC) 40% sand, 30% clay, 30% silt D) 50% sand, 10% clay, 40% silt*
15Using the triangular graph of soil texture, a soil texture combination of 20% sand, 10% clay and 70% silt would constitute which soil type? (A) sandy clay (B) sandy loam (C) silty clay (D) silty loam*
16Using the triangular graph of soil texture below, which combination would make the most favourable soil for farming? (A) 10% sand, 15% clay, 75% silt (B) 15% sand, 55% clay, 30% silt (C) 20% sand, 70% clay, 10% silt (D) 50% sand, 20% clay, 30% silt*
17Soil texture…resultsSandy soil — very light & dries out swiftly. Water drains very quicklySilty soil — retains moisture & feels slippery when wet. Retains nutrients better than sand but does not dry out as quickly.
18Soil texture…resultsClay soil — a very heavy soil, it holds moisture for long periods of time when wet and dries hard as a brick. .Loam soil — the ideal soil texture, it is composed of sand, silt and clay. Loam is a separate category because none of its components account for more than 50%.
19Hand TexturingUsed to determine the relative contributions of the fine fraction.Very useful in the field to determine soil texture.Based on physical properties and “feel”.Sand feels gritty as you can feel the individual particles. Silts are smooth, and clays are sticky.
20Start by Making a Ball 1. Falls apart? SAND (or not enough water) Does not fall apart? Continue by making a ribbon.2. Will not form ribbon? LOAMY SAND3. Ribbon breaks <2.5cmSANDY LOAM, SILTY LOAM or LOAM4. Ribbon moderately sticky, firm, 2.5 – 5.0 cmSANDY CLAY LOAM, SILTY CLAY LOAM or CLAY LOAM5. Ribbon sticky and firm, >5.0 cmSANDY CLAY, SILTY CLAY or CLAY
23Soil Characteristics Most soils contain four basic components: Organic matterMineral particlesWaterAir
24Soil Characteristics - Organic Content: Plants and animals aid in the development of a soil through the addition of organic matter (Ie. When they die!).Fungi and bacteria decompose this organic matterAlso known as humus. A source of nutrients for plant growth.Makes up the upper layer of the soil .Colored dark brown to black.
25Soil Characteristics - Mineral content Originally part of rocksBroken down by weathering of rockDifferent particle sizes (sand, silt and clay)Some minerals are nutrients needed by plants for growth. (Calcium, potassium, phosphorous)
26Soil Characteristics – Water & Air About half of the total mass of soil is made of up vast interconnecting cavities or holes.Usually caused by worms, insects and small animals that tunnel through the soil.These holes are filled with both air and water.The amount of air and the amount of water filling these spaces varies dramatically throughout the year, and from location to location.BUT averages about half each.
27Soil Characteristics – Water & Air Plants need air around their roots in order to properly obtain nutrients required for growth.Plants need water to grow.Water enables physical and chemical weathering to create the various components of the soil.Water dissolves and carries minerals and nutrients required by plants to grow.