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Explore the integration of living systems in soil, compare sand, clay, and loam soils, and learn about soil degradation, conservation, and management in commercial and subsistence farming. Soil components and types are outlined for comprehensive understanding.
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•3.4.1: Outline how soil systems integrate aspects of living systems •3.4.2: Compare and contrast the structure and properties of sand, clay, and loam soils including their effect on primary productivity •3.4.3: Outline the processes and consequences of soil degradation •3.4.4: Outline soil conservation measures •3.4.5: Evaluate soil management strategies in a named commercial farming system and in a named subsistence farming system Humus Topsoil Subsoil Regolith Bedrock – granite in this case.
Duff : the layer of partially and fully decomposed organic materials lying below the litter and immediately above the mineral soil. It corresponds to the fermentation (F) and humus (H) layers of the forest floor. When moss is present, the top of the duff is just below the green portion of the moss Parent material: The primary material from which the soil is formed. Soil parent material could be bedrock, organic material, an old soil surface, or a deposit from water, wind, glaciers, volcanoes, or material moving down a slope.
Constituents of healthy soil • Native inorganic material: • Rock, sand, silt, clay, air, and water • Organic sediment: • Decomposing plant material
Soil is composed of particles of broken rock that has been altered by chemical and mechanical processes that include weathering, erosion and precipitation. • Ex. of mechanical erosion is “freeze and thaw” • Chemical weathering includes reactions such as iron and water (rusting) • Soil is altered from its parent rock due to interactions between the lithosphere, hydrosphere, atmosphere, and the biosphere.
Soil quality is a good indicator of a healthy ecosystem. • The soil stores water for use by plants and filters our ground water and surface water. • We depend on the soil to provide us with food and fiber. Soils play a major role in recycling carbon and nitrogen.
About 11,000 years ago, near the end of the last Ice Age, glacial meltwaters deposited the sand and gravel outwash that forms the lower subsoil and substratum of the soil in areas like the Great Plains. Strong winds and glacial meltwaters then deposited 2 to 3 feet of silty loess and loamy outwash on top of the sand and gravel. Soil development, under hardwood forests, produced an organic enriched surface layer and a clay enriched subsoil.
Sandy Soils • Sandy Soils have a gritty texture and are formed from weathered rocks such as limestone, quartz, granite, and shale. • If sandy soil contains enough organic matter it is easy to cultivate, • however it is prone to over-draining and summer dehydration, • and in wet weather it can have problems retaining moisture and nutrients.
Formation of Sand – mostly due to mechanical weathering during transport by rivers and/or wind. • As pieces of rock are carried downstream they collide with and are worn by other rocks. • Well-sorted sand, such as at a beach, has had all of the smaller particles (silt) removed by the action of waves. • Wind can also act as a sorting mechanism resulting in sand.
Silty Soil • Silty soil is considered to be among the most fertile of soils. • Usually composed of minerals (predominantly quartz) and fine organic particles, • it has more nutrients than sandy soil yet still offers good drainage. • When dry it has rather a smooth texture and looks like fine-grained sand. • Its weak soil structure means that it is easy to work with when moist and it holds moisture well.
Formation of Silt – extreme mechanical weathering. • The erosive action of glaciers acting on bedrock leads to the formation of significant amounts of silt. • Streams that emerge from glaciers are typically white and cloudy because of large amounts of silt suspended in the water.
Clay Soil • When clay soils are wet they are very sticky, lumpy and pliable but when they dry they form rock-hard clots. • Clay soils are composed of very fine particles with few air spaces, • thus they are hard to work and often drain poorly - they are also prone to water logging in spring. • Blue or grey clays have poor aeration and must be loosened in order to support healthy growth. • Red color in clay soil indicates good aeration and a "loose" soil that drains well. • As clay contains high nutrient levels plants grow well if drainage is adequate.
Clay formation – the chemical weathering of larger particles such as sand, silt, volcaniclasts, etc. • Acids and/or bases in help degrade particles into clays. • Clays are high in minerals but are typically hard to release because they are chemically attached to the clay particles.
Loamy Soil • Considered to be the perfect soil, • Loamy soils are a combination of roughly 40 % sand, 40% silt and 20% clay. • Loamy soils can range from easily workable fertile soils full of organic matter, to densely packed sod. • Characteristically they drain well, yet retain moisture and are nutrient rich, making them ideal for cultivation.
Soil is mixture of what?... • Mineral particles (from rock) • Organic remains (dead plants and animals) • Water • Air
Soil Degradation The roots of this Indian grass reached ten feet into Kansas earth, anchoring prairie soil and leaking plant sugars that nourished fertility-enhancing microorganisms. One acre of roots can weigh as much as a school bus.
Soil Degradation – two main processes: Erosion – when vegetation is removed from soil and exposure to wind and water runoff take away topsoil. Soil abuse – overuse of agricultural chemicals, improper irrigation, mechanical compaction.
Soil Erosion Three main types:
Human activities that enhance these processes: 1. Overgrazing – hooves of ungulates compact soil. Vegetation is removed by consumption. Issues are exacerbated by drought. Example – Sahel in 1970s-80s. 2. Overcropping – leads to depletion of nutrients. Plants have difficulty recovering. Example – dust bowl of 1930s. 3. Deforestation – forests exist in rainy areas. Trees have adaptations to reduce the effects of water runoff and erosion. When trees are removed erosion increases dramatically.
Unsustainable agriculture Total removal of crops, leaving soil bare. Row cropping with uncovered soil between. Ploughing in direction of slope. Excessive use of pesticides. Irrigation.
Soil Conservation Adding soil conditioners: Lime, green manures, straw, other nutrient rich organics Wind reduction: Trees, bushes, fencing. Cover cropping: Clover Terracing Improved irrigation techniques Stop ploughing marginal land Crop rotation
