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A.P. Environmental Science - Soil Quality
Terms in this set (47)
-Soils are dynamic ecosystems composed of a combination of minerals, organic matter, and living organisms.
-The variety of soil types is the result of the diversity of minerals and organisms (mainly bacteria) that compose them.
-Soils form continuously, but very slowly. Only about one inch of soil is formed every 500 to 1,000 years, so loss of good topsoil is a serious concern.
Soils are created over long time scales through the weathering of rocks by wind and rain. In addition to minerals from the weathering of rocks, soils contain organic matter, called humus, from the decomposition of plants and animals
Components of a Typical Soil
-45% mineral (Si, Fe, Al, Ca, K, Mg, Na)
The two most abundant elements in the earth's crust are O
(47%) and Si (27%)
Quartz = SiO2
Clay minerals are aluminum silicates
Nonsilicates = NaCl, CaSO4 (gypsum), CaCO3 (calcite)
-50% pore space
-1 to 5% organic matter
Soils consist of four main mineral types:
Sand, Silt, Loam and Clay describe the texture of a soil.
Affects the movement of water and air through the soil
Affects root penetration (looseness and workability)
Soil porosity refers to the amount of pore, or open space between soil particles. Pores are created by the contacts made between irregular shaped soil particles. Fine textured soil has more pore space than coarse textured because you can pack more small particles into a unit volume than larger ones. More particles in a unit volume creates more contacts between the irregular shaped surfaces and hence more pore space. As a result, fine textured clay soils hold more water than coarse textured sandy soils.
One important point to remember is that the diameter size of the grain does not affect porosity. Remember, porosity is a ratio of void space to total volume. A room full of ping pong balls would have the same porosity as a room full of basketballs, as long as the packing or arrangement are similar.
The degree of connectivity between soil pores. A highly permeable soil is one in which water runs through it quite readily. Coarse textured soils tend to have large, well-connected pore spaces and hence high permeability.
-The ultimate degradation of organic matter
-Humus has a three dimensional sponge-like structure that can absorb water and solutes in the water. Humus is only slowly utilized by soil organisms and has a turnover rate of 1 to 2% per year. In general soils with higher organic matter contents have higher numbers of microbes and higher levels of activity.
-Humus shares two properties with clay: it is highly charged and it has a large surface area to volume ratio.
The quantity of organic matter found in soil depends on climate. Soils found in temperate climates with high rainfall have increased levels of organic matter. Levels of organic matter found in soil range from essential no organic matter (Yuma, AZ) to 0.1% organic matter (Tucson, AZ) to 3 to 5% organic matter (midwest) to 20% organic matter (bogs and wetlands).
Where are the bacteria?
In soil 80 to 90% of the bacteria are attached to surfaces and only 10-20% are planktonic. Cells have a patchy distribution over the solid surfaces, growing in microcolonies. Colony growth allows sharing of nutrients and helps protect against dessication and predation or grazing by protozoa
The richest soils are loamy soils in which there is a high concentration of primary nutrients: Nitrogen (N), Phosphorus (P), Potassium (K).
calcium (Ca), magnesium (Mg), and sulfur (S). There are usually enough of these nutrients in the soil so fertilization is not always needed. Also, large amounts of Calcium and Magnesium are added when lime is applied to acidic soils
The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants.
Nitrogen is a part of all living cells and is a necessary part of all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy.
Nitrogen is a part of chlorophyll, the green pigment of the plant that is responsible for photosynthesis.
Helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops.
Nitrogen often comes from fertilizer application and from the air (legumes get their N from the atmosphere, water or rainfall contributes very little nitrogen)
-Deficiency can cause yellow leaves and deficient growth
phosphorus (P) is an essential part of the process of photosynthesis.
Involved in the formation of all oils, sugars, starches, etc.
Helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress.
Effects rapid growth.
Encourages blooming and root growth.
Phosphorus often comes from fertilizer, bone meal, and superphosphate.
-A deficiency can cause purple leaves, stunted growth, and seed sterility.
any of various mined and manufactured salts that contain potassium in water-soluble form. The name derives from "pot ash", which refers to plant ashes soaked in water in a pot, the primary means of manufacturing the product before the industrial era. The word "potassium" is derived from potash
Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium.
Helps in the building of protein, photosynthesis, fruit quality and reduction of diseases.
Potassium is supplied to plants by soil minerals, organic materials, and fertilizer.
-A deficiency can cause mottling, spotting, streaking or curling of leaves
-The most important chemical property of the soil (texture is the most important for physical properties)
-Knowing the pH of the soil will quickly allow you to determine if the soil is suitable for plant growth and what nutrients will be most limiting.
-* pH - the negative log of the hydrogen ion(H+) concentration in the soil water solution.
pH = - log [ H+]
* the pH scale is how we measure acidity and alkalinity of solutions. at neutral (pH =7) the number of H+ = OH-
at pH of 6 there are 10x more H+ ions than at a pH 7
and there are 100x more H+ ions between pH 7 & 5
-The pH of soil or more precisely the pH of the soil solution is very important because soil solution carries in it nutrients such as Nitrogen (N), Potassium (K), and Phosphorus (P) that plants need in specific amounts to grow, thrive, and fight off diseases.
If the pH of the soil solution is increased above 5.5, Nitrogen (in the form of nitrate) is made available to plants. Phosphorus, on the other hand, is available to plants when soil pH is between 6.0 and 7.0.
-If the soil solution is too acidic plants cannot utilize N, P, K and other nutrients they need. In acidic soils, plants are more likely to take up toxic metals and some plants eventually die of toxicity
Excess Soluble/Available Aluminum
Excess soluble/available aluminum (Al+++) is toxic to plants and causes multiple other problems. Some of the more important problems include...
• Direct toxicity, primarily seen as stunted roots
• Reduces the availability of phosphorus (P), through the formation of Al-P compounds
• Reduces the availability of sulfur (S), through the formation of Al-S compounds
• Reduces the availability of other nutrient cations through competitive interaction
Soil quality can be distinguished by color, which is determined by the availability of oxygen and the presence of iron. Red and yellow soils indicate that the soils are well aerated, that is, they are porous and have a substantial amount of oxygen. Poorly aerated soils are gray or olive.
As soils form over time, layers build up, called horizons, which have different characteristics and composition.
Soils of the Rainforest
Tropical soil is identified as having three distinct soil attribute types: shallow nutrient depth, lacking in nutrients and devoid of soluble mineral content. In other climates soils store the nutrients and minerals necessary for plant life, but this is not the case with tropical soils. It is for these reason that tropical rainforest deforestation is so devastating to tropical ecosystems
Soil Cation Exchange Capacity
Cation Exchange - the ability of the soil to hold onto nutrients and prevent them from leaching beyond the roots.
Cations are "+ "charged ions = Ca++, Mg++, K+, NH4+(ammonium),
The more cation exchange a soil has the more likely the soil will have a higher fertility level.
The Cation Exchange Capacity (CEC) in laymen's terms is basically a rating of the soil's ability to hold nutrients or a fertility-holding capacity. The CEC number represents milliequivalents (ME) and can be thought of as a storage battery holding volts of electricity. The higher the number, the more storage capacity or milliequivalents the soil can hold.
High CEC soils hold nutrients longer, prevent leaching, maintain high microbial activity and help hold moisture in the root zone area. The only practical way to increase the CEC rating of a soil would be to increase humus levels. This can be achieved by adding organic matter such as compost, returning harvest residues, growing permanent cover crops or applying carbon based fertilizers. Fertile soils should have an organic content of 2 to 5 percent.
It should be noted that most fertilizer chemicals can rapidly destroy soil humus. Examples are sulfuric acid, anhydrous ammonia, and salt-based fertilizers. Many pesticides may effect the same destruction.
A high CEC value (>25) is a good indicator that a soil has a high clay and/organic matter content and can hold a lot of cations.
Soil with a low CEC value (<5) is a good indication that a soil is sandy with little or no organic matter that cannot hold many cations.
The interchange between a cation in solution and another cation on the surface of any negatively charged material such as clay or organic matter
Sources of acidity in Soil
Nitrification: Ammonium to Nitrate (oxidation of NH4+)
NH4+ + 2O2 ---> NO3- + H2O + 2 H+
2. Organic material decomposition
organic acids ionized :
R-COOH---> R-COO- + H+
respiration: CO2 + H2O ----> H2CO3 = H+ HCO3-
In agriculture, leaching refers to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation.
Percent Base Saturation
H+ and Al 3+ are known as acidic cations
Ca 2+, Mg2+, K+, Na +, and NH4+ are known as basic cations
-Percent base saturation reflects the proportion of the CEC that is occupied by basic cations:
%base saturation = Base Cations / CEC * 100
Access to fresh water
The soil in flood plains is usually fertile
The terrain lends itself to easy development on flat land
Floodplains are close to rivers for easy transportation
arable land (from Latin arare, to plough): land that can be used for growing crops.
Of the earth's 148,000,000 km² (57 million square miles) of land, approximately 31,000,000 km² (12 million square miles) are arable; however, arable land is currently being lost at the rate of over 100,000 km² (38,610 square miles) per year
Loss of arable land
- Salinization / Waterlogging
a frequent unintended result of irrigation. It occurs when salts drawn up from the subsurface (or introduced in irrigation water) are left behind in the topsoil when the water evaporates. As salts accumulate, the land is rendered less productive and in extreme cases becomes entirely unfit for cultivation.
1.Irrigation water contains small amounts of dissolved salts
2. Evaporation and transpiration leave salts behind
3. Salt builds up in soil
Remediation of salinization
The primary method of controlling soil salinity is to permit 10-20% of the irrigation water to leach the soil, be drained and discharged through an appropriate drainage system. The salt concentration of the drainage water is normally 5 to 10 times higher than that of the irrigation water, thus salt export matches salt import and it will not accumulate.
Waterlogging refers to the saturation of soil with water. Soil may be regarded as waterlogged when the water table of the groundwater is too high to conveniently permit an anticipated activity, like agriculture.
In agriculture, various crops need air (specifically, oxygen) to a greater or lesser depth in the soil. Waterlogging of the soil stops air getting in. How near the water table must be to the surface for the ground to be classed as waterlogged, varies with the purpose in view. A crop's demand for freedom from waterlogging may vary between seasons of the year, as with the growing of rice
1.Precipitation and irrigation water percolate downward
2. Water table rises
Salinization and Waterlogging of Soils: A Downside of Irrigation
Example of high evaporation, poor drainage, and severe salinization.
White alkaline salts move
Soil salination is the accumulation of free salts to such an extent that it leads to degradation of soils and vegetation.
Salination is a natural process that results from:
high levels of salt in the soils.
landscape features that allow salts to become mobile (movement of water table)
climatic trends that favor accumulation
Desertification: Degrading Drylands
About one-third of the world's land has lost some of its productivity because of drought and human activities that reduce or degrade topsoil.
a type of land degradation in which a relatively dry land region becomes increasingly arid, typically losing its bodies of water as well as vegetation and wildlife
Because of wasteful and polluting practices in growing cotton by the Soviet Union, the Aral Sea in the former Soviet republic of Uzbekistan has shrunk dramatically and to devastating effect on the local population
Coccidioidomycosis (Valley Fever)
-Caused by dust bowl
Making Soils Sustainable
-Best Management Practices (BMP's)
-Protect Riparian Zones (Buffer Strips)
--Practice Sustainable Grazing
-Land is plowed along contours, perpendicular to the slope, and as much in the horizontal plane as possible.n
-Most effective in reducing erosion
-Protect Riparian Zones
forestland left relatively undisturbed to lessen visual or environmental impacts of timber harvesting, usually along a road or waterway
Carving small, flat plots of land from hillsides to use for farming
"Steps" carved into mountains to make the land flatter for farming.
Protective groundcover that protects the soil, saves water, and prevents weed growth.
-Protect crop from wind erosion
rows of trees planted as a windbreak to reduce soil erosion of agricultural land
Practice Sustainable Grazing
-Regulate stocking rates to sustain
Storing water in the soil during on crop growing season for use by a crop planted the next season
The farming practice of leaving land idle for a year or more to accumulate sufficient soil moisture to produce a crop or to restore soil fertility; summer fallowing is being replaced by continuous cropping.
Crops are rotated with cover
The practice of rotating use of different fields from crop to crop each year, to avoid exhausting the soil.
Plant Perennial Grains
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