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Soil Science Exam 2
| Question | Answer |
|---|---|
| Define soil | A relatively thin surface layer made up of a mixture of weathered mineral particles, decaying organic matter, living organisms, gases, and liquid solutions. |
| what are the 5 factors of soil formation? | CL - climate O - organisms (Vegetation/Biology) R - Relief(Topography) P - Parent Material T - Time |
| How does soil contribute to climate change? | Peats and marshes hold large amounts of methane which are released with soil degredation and climate change. |
| How can soil help mitigate climate change? | Humus can adsorb pollutants and pesticides (reacts w/metal ions forming chemical complexes that can mitigate the toxicity). Soil acts as a huge carbon sink and can be used more effectively through better farming practices. |
| Functions of soil OM | Improves soil structure: Organic matter acts as a glue, clumping soil particles into aggregates that create pore spaces for air and water and reduce compaction. Increases water infiltration and holding capacity, Reduces erosion. |
| What consumes soil OM? | Microbes |
| Humus (colloidal) | 5 yrs + mean residence time (shortened by tillage), About 58% C, 5% N, Releases nutrients slowly in the soil, Complex chemical structure (hard to break down), negative charge, high CEC, Adsorbs to mineral particles, gluing together soil aggregates. |
| Universal Soil Loss Equation | A = R K LS C P. |
| How to conserve soil OM | Reduced (minimum) tillage, Cover crops, Growing high residue crops, Adding OM to soils, Practicing crop rotation |
| What are problems or issues with adding OM? | Low value (transportation cost), N in manures is subject to loss as NH3, Significant danger of off-site transport by erosion, Eutrophication, fouling of streams, Timing of availability and need. |
| What soil properties does acidity affect? | chemical, physical, and biological properties of soils, Nutrient availability (optimum pH for most crops is 5.5 - 7), Metal toxicity and solubility e.g., Al toxicity at pH <5.5 (also Mn solubility and toxicity), Microbial activity (important in N cycle) |
| define and explain salinity | The presence of electrolytic solutes in high enough concentrations that are harmful to plants. This salt can get there through rainwater, irrigation, acid rain, sea spray, chemical reaction in underlying rock etc... |
| What makes a nutrient essential? | nutrients needed to carry out growth and reproductive success – a full life cycle. • Omission of the element will result in abnormal growth • The element cannot be replaced or substituted • The element must exert its effect directly on growth |
| What are plant nutrients? | Plants require nutrients that are not created through photosynthesis • H, O, C - Plants get from air and water Macronutrients • N, P, K - High amounts • Ca, Mg, S - Lesser amounts Micronutrients • Fe, Mn, B, Mo, Cu, Zn, Cl, Co |
| What are 3 forms nutrients are present in the soil? | 1. Readily bioavailable 2. Labile reserve 3. Stable reserve |
| NPK and their importance in soil | Nitrogen, Phosphorous and Potassium, Macronutrients of the soil so a lot is needed. |
| What are the benefits of soil biodiversity? | This diversity imparts the soil with the ability to respond to and recover from: • Flooding • Drought • Pollutants • It enhances soil stability and resilience. • Easier to maintain than to restore (no-till or low-till) |
| Mycorrhizae | symbiotic relationships that form between fungi and plants. Fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis |
| What is tillage? | The mechanical manipulation of soil aimed at improving conditions for crop production. |
| When did ‘Slash and Burn’ actually work? | It worked in tropical oxisols or soils with low ability to grow crops and would only work for 3-5 years before people needed to move somewhere else to grow until it was replenished. Only worked with small population that wouldn't overuse this land. |
| Positive and negative effect of irrigation | Irrigation agriculture cannot be sustained indefinitely without stringent requirements for effective prevention of upstream, on-site, and downstream environmental damage like Waterlogging and Salinization. |
| POPS | Persistent organic pollutants (POPs) are a group of toxic chemicals that don’t break down easily in the environment. Intentionally produced and used in agriculture, disease and pest control, manufacturing, or industry. |
| Colloids | Microscopic soil particles. Most chemically active fraction of soils. Remain suspended when mixed with water, appearing as a murky solution. Attract and hold large number of water molecules, due to the polar nature of water molecules. |
| CEC definition | A measure of the ability of a soil to hold and exchange cations. |
| Base Saturation | The percentage of the soil’s CEC (on a charge equivalent basis) that is occupied by basic cations (Ca2+, Mg2+, K+, and Na+) |
| Matric potential | Work required to remove water held by adhesion to soil surface and cohesion in capillary pores. |
| Osmotic potential | If there are solutes in the solution, water will group around them and reduce the freedom of water movement, i.e., lowering the potential. |
| Gravitational water | Water drains right through. |
| capillary water | Water held in micropores (available water, plants roots can absorb this). |
| hygroscopic water | Remaining water adheres to soil particles. |
| wilting point | Where there is no more water available for plants. End of available water. |
| field capacity | The amount of water a soil can hold after being saturated and allowed to drain under gravity for one to two days. |
| SOM composition | <5% living organisms, <10% fresh residue, 33-50% Decomposing organic matter (active fraction), 33-50% stabilized organic matter (humus) |
| How does acidity affect soil? | Not an attribute of the soil’s solid phase (the particles) but the soil solution. Results from interaction of the adsorbed and exchangeable ions of clay fraction with the water present. |
| Readily bioavailable nutrients | present in the soil solution within the active rooting zone (small fraction) |
| Labile reserve nutrients | adsorbed in the soil’s exchange complex and/or present in rapidly decomposable OM (large fraction) |
| Stable reserve nutrients | present in relatively unweathered soil minerals and slowly decomposing humus |
| Nitrogen | Most of soil nitrogen is in the form of OM • Promotes growth and color • Excess causes excessive growth, weak stems |
| Phosphorous | Primary source: specific minerals, OM, bones and teeth (both organic and inorganic forms). Promotes seed development, reproduction, cell division, metabolic processes. Enhances root development and water uptake by the roots. |
| Phosphorous problems | Added P does not remain available for long, tends to convert to insoluble forms (reaction with Ca, Fe, or Al). Excess may lead to deficiencies in other nutrients |
| Potassium | Source in soil: mineral weathering. (can be completely weathered away in well developed soils like Ultisols and Oxisols). Increases winter hardiness. Regulator of drought tolerance, reduces diseases, important in ripening of fruits and vegetables |
| What are the aims/goals and what are the best practices for tillage? | Control weeds, Incorporate OM, Improve soil structure. Site specific (fragipan and hardpans need to be broken). Modern goal is zero tillage or precision tillage for soil structure management. |
| Precision farming | A balanced combination of practices designed to optimize nutrient supply, tillage, water use, and pest control. |
| Primary tillage | Slice and lift the soil along parallel furrows and invert it to cover surface residues, usually to 20cm depth. The objective of primary tillage is to attain a reasonable depth of soft soil, incorporate crop residues, kill weeds, and to aerate the soil |
| Secondary tillage | light tillage, to eradicate weeds and loosen soil, less than 20cm depth. But can grind down the soil aggregates – not good. Secondary tillage is any subsequent tillage, to incorporate fertilizers, reduce the soil to a finer tilth, level the surface. |
| Is tillage good? | There is no study to show that this improves crop growth or soil health, it actually worsens health and the best practices are minimal to no tillage. Also the more heavy the tilling the more energy it takes for less gain. |
| Soil degradation causes | is a decline in soil quality due to misuse, usually from agricultural, pastoral, industrial or urban purposes. |
| Soil degradation prevention | Windbreaks like shrubs, terracing of slopes to reduce water runoff and conserves rainwater, strip farming like alternating strips of diff types of crops, crop rotation to + soil nutrients and vegetating bare slopes. |
| Soil degradation mitigation | Bioremediation (vegetation uptake and removal or microbial inoculation and composting) Excavate and incinerate. Leaching (for soluble compounds). Venting or vapor extraction |
| Soil degradation results | Erosion is the most severe of soil degradation because it is IRREVERSIBLE. Wind in dry regions Water in humid regions 1. Detachment of particles 2. Transport suspended in flowing water or blowing wind 3. Deposition - sedimentation |
| Desertification | Not expansion of the desert, but from population centers outside of the desert. As land degrades from misuse It is worked or grazed more intensely. Degradation is exacerbated ,then new land in marginal areas is brought under cultivation or grazing |
| pollution causes | Seepage from a landfill, Discharge of industrial waste into the soil, Percolation of contaminated water into the soil, Rupture of underground storage tanks or pipelines, Excess application of pesticides, herbicides or fertilizer. Solid waste seepage |
| Most common chemicals causing soil pollution | Petroleum hydrocarbons Heavy metals Pesticides Solvents |
| Inorganic toxic compounds | Copper, mercury, cadmium, lead, nickel, arsenic are the elements which can accumulate in the soil, if they get entry either through sewage, industrial waste or mine washings. Some of the fungicides containing copper and mercury also add to soil pollution. |
| How can inorganic toxicity be minimized? | Toxicity can be minimized by building up soil organic matter, adding lime to soils and keeping the soil alkaline. |
| Organic wastes | Domestic garbage, municipal sewage, and industrial wastes. Organic wastes contain borates, phosphates, detergents in large amounts. The main organic contaminants are phenols and coal. |
| How are POPS bad | POPs can travel regionally and around the world. Bioaccumulate in the fat tissue of humans and animals, biomagnify in food chains, and are persistent in the environment. |
| Water Content | Total amount of water in the soil. Does not indicate how much is available to a plant. |
| Water Potential | The amount of energy needed to extract water from soil. Direct measure of how much water is available to a plant. |
| Kinetic Energy in water | When water (not soil water) is flowing in a river in rapid and turbulent flows. |
| Potential Energy | Determines the status and movement of soil water (moving very slowly). Like all substances, soil water move from higher to lower energy level. |
| Gravitational Potential | Work required to draw water down in response to gravity. Applies to gravitational water only. |
| Hydrostatic Potential | Work required to move water below the water table; applies only to saturated conditions. |
| How does osmotic potential affect soil solution and plants? | Water containing salts is less able to do work than pure water, so the more salts the lower the potential. In “salty” soil, potential in soil solution may be lower than inside plant root cells, impeding ability of water to pass into plant |
| Saturated flow of soil water | When soil pores are completely filled with water. Saturated flow decreases as the pore size decreases. Generally, the rate of flow in soils of various textures is in the following sequence Sand > loam > clay |
| Where does saturated flow occur? | Occur in aquifers (water - bearing sediments and rock layers), in flooded soil and in lower horizons of soil with limited drainage |
| Unsaturated flow of soil water | Driving force is through the matric potential gradient. Movement in the direction of moist soil to dry soil and from thick moisture- to thin moisture-films. In downward movement, capillary and gravitational potentials act together. |
| how does Unsaturated flow of soil water work? | Unsaturated conductivity is a function of soil moisture content, number, size and continuity of soil pores. When the continuity of the films is broken, liquid flow stops. Wetter the soil, the greater the conductivity for water. Sand < loam < clay. |
| Transpiration | loss of water vapor to the atmosphere from Stomata (pores) on leaves. |
| Do roots require energy? | No, roots are passive and get water through osmosis and then the water is pulled out the leaf tips through transpiration at the end. |
| Inorganic colloids | – clay minerals – Thin, platelike forms – Created by chemical alteration of larger particles |
| Organic colloids | – Humus – Decomposed OM |
| Adhesion | Attracts water to soil particles, so particles close to soil are at lower energy state because it's stuck there (not moving anywhere). |
| CO2 | Preindustrial norm was 275 ppm now is 423 ppm. Very long lived and agriculture is 1% of Anthropogenic CO2 emissions. |
| CH4 | Methane has a lower concentration than carbon dioxide but is 20x stronger, accounts for 16% of warming of effect. Has more than doubled since industrialization. Agriculture accounts for 47% of this methane. |
| N2O | 300x stronger than CO2, mostly from excessive or untimely use of fertilizers. 84% of this results from agriculture. |
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