Soil Soil Characteristics Understand what soil is and

Soil

Soil Characteristics Understand what soil is and how it forms. Compare and contrast the characteristics of different soils. What type do you have around your house? 1) clay = “layer silicates that are formed as products of chemical weathering of rocks, usually sedimentary rock. ” 2) silt = rock worn into tiny pieces (coarser than clay, but finer than sand). usually 1/20 millimeter or less in diameter 3) sand = quartz or silica worn down over time. grains with diameters between 0. 06 mm to 2 mm 4) organic matter (humus) 5) Loam = soil containing a mixture of clay, sand, silt and humus. Good for growing most crops.

Soil Types: relative sizes

Soil Porosity and Permeability Porosity - volume of water that “fits between” the soil particles Permeability - rate of flow of water through soil % retention - how much water is “trapped” by soil Porosity and Permeability are directly related; when one is high, the other is high as well. % water retention is inversely related to both. _______________________________ 1) Clay - porosity permeability, retention 2) Silt - porosity, permeability, retention 3) Sand - porosity, permeability, retention 4) Organic matter - porosity, permeability, retention

Soil Horizons

Soil Formation Soil formation - Parent material is slowly broken down by biological, chemical and physical weathering. Biological - Respiration of plant roots and other organisms produce CO 2, which reacts with soil water to produce carbonic acid (H 2 CO 3). Chemical - Acids crack rocks water seeps in breaks down particles. Physical - Weathering introduces water that breaks down particles. Time scale - Formation of 2. 5 cm of topsoil takes 200 - 1000 yrs.

Soil Formation

Soil Composition 45% Mineral particles (broken down pieces of rock) 5% Organic matter (humus - from dead organisms, worm castings, leaf litter) 25% Water (precipitation) 25% Air (More with sandy soil, less with clay soil) Soil organisms - Millions in one teaspoon of fertile agricultural soil! - bacteria, fungi, algae, microscopic worms. provide ecological services such as worm castings, decomposition to humus, breaking down of toxic materials, cleansing water, nutrient cycling from decomposers or upon death

Soil Texture Loam - ideal agricultural soil 40% sand (larger - structural support, aeration, permeability) 40% silt (smaller - holds nutrient minerals and water) 20% clay (even smaller - holds nutrient minerals and water) Plants grown in sandy soils More susceptible to mineral deficiencies and drought Plants grown in clay soils More susceptible to waterlogging, and oxygen depletion (think small pore size, low porosity)

Soil Composition

Soil Texture Triangle

Soil Acidity (p. H) p. H - concentration of H+ ions (4 -8 in healthy soil) Affects solubility of nutrient minerals Low p. H-Aluminum and Manganese are more soluble, may absorb too much High p. H increases leaching of important ions such as K+ Causes of changes - acid rain, decomposition, leaf litter, mining (acid sulfate soils) Remediation - Too high p. H, add acidic leaf litter - Too low p. H, add lime

What different sorts of fertilizers are available? Organic… manure adds N and soil bacteria & fungi green manure compost mushroom spores Inorganic… 1/4 th of the world’s crops depend on this. N, K, P Experimental data comparing methods!

Soil Nutrients (NPK)

Inorganic Fertilizer Inorganic - Manufactured from chemical compounds (fast-acting, short-lasting) Highly soluble so immediately available to plants High solubility also makes it leach quickly (pollutes water) Suppresses growth of microorganisms Source of gases that increase air pollution Production requires much energy from fossil fuels

Organic Fertilizer Organic - animal manure, bone meal, compost (slow-acting, long-lasting) Delay in availability to plants, needs time for the organic material to decompose Delay causes low level of nutrient leaching Improves water holding capacity