Soil & Agriculture

Soil & AgricultureTextureThe percentages (by weight) of different sized particles of sand, silt and clay that it contains.

Soil Properties:2StructureHow soil particles are organized and clumped together. (Sand, silt, clay)3FriabilityHow easily the soil can be crumbled.4PorosityA measure of the volume of soil and the average distances between the spaces.5PermeabilityThe rate at which water and air moves from upper to lower soil layers. It is distances between those spaces.

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Some Soil PropertiesSoils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them.Figure 3-257Shrink-Swell PotentialSome soils, like clays, swell when H2O gets in them, then they dry and crack. This is bad for house foundations, etc.

8pHThe pH of most soils ranges from 4.0 to 8.0. But, the soil of the Pygmy Forest in California is extremely acidic (2.8-3.9) and in Death Valley, California, it is very basic (10.5). Plants are affected by pH because of the solubility of nutrient minerals.9SlopeSteep slopes often have little or no soil on them because of gravity. Runoff from precipitation tends to erode the slope also. Moderate slopes and valleys may encourage the formation of deep soils.10DepthSome soils are very shallow (like in some places in San Antonio). It can be only two inches of soil and then you hit rock. Other areas can have soil 36 inches deep or more.11ColorDark soil is rich with lots of organic matter. Light soil (like sand) is not so rich with very little organic matter.12

Fig. 3-23, p. 68FernMature soilHoney fungusRoot systemOak treeBacteriaLords and ladiesFungusActinomycetesNematodePseudoscorpionMiteRegolithYoung soilImmature soilBedrockRockfragmentsMoss and lichenOrganic debrisbuilds upGrasses and small shrubs Mole Dog violetWoodsorrelEarthwormMillipedeO horizonLeaf litterA horizonTopsoilB horizonSubsoilC horizonParent materialSpringtailRed Earth Mite13Figure 3.23Natural capital: soil formation and generalized soil profile. Horizons, or layers, vary in number, composition, and thickness, depending on the type of soil. (Used by permission of Macmillan Publishing Company from Derek Elsom, Earth, New York: Macmillan, 1992. Copyright 1992 by Marshall Editions Developments Limited)Organic Layer (O-horizon)The uppermost layer; it is rich in organic material. Plant litter accumulates in the O-horizon and gradually decays. In desert soils the O-horizon is completely absent, but in certain organically rich soils it may be the dominant layer.14Topsoil (A-horizon)It is dark and rich in accumulated organic matter and humus.It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching.

15Subsoil (B-horizon)The light-colored subsoil beneath the A-horizon; it is often where nutrient minerals have leached out of the topsoil and litter accumulate. It is typically rich in iron and aluminum compounds and clay.

16Parent Material (C-horizon)This contains weathered pieces of rock and borders the unweathered solid parent material. Most roots do not go down this deep and it is often saturated with groundwater.

17Layers in Mature SoilsInfiltration: the downward movement of water through soil.Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers.The soil type determines the degree of infiltration and leaching.186.4 billion tons of soils are eroded from the U.S. each year; this would fill 320 million average-sized dump trucks that, if parked end-to-end, would extend to the moon and of the way back!Erosion19DefinitionErosion is the movement of soil components, especially surface litter and topsoil, from one place to another.20ImportanceIn undisturbed ecosystems, the roots of plants help anchor the soil, and usually soil is not lost faster then it forms.

Erosion destroys in a few decades what nature took hundreds to thousands of years to produce.21Global Outlook: Soil ErosionSoil is eroding faster than it is forming on more than one-third of the worlds cropland.Figure 13-10

22SOIL EROSION AND DEGRADATIONSoil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water.Soil erosion increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles.Figure 13-9

23SOIL EROSION AND DEGRADATIONSoil erosion lowers soil fertility and can overload nearby bodies of water with eroded sediment.Sheet erosion: surface water or wind peel off thin layers of soil.Rill erosion: fast-flowing little rivulets of surface water make small channels.Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies.24Wind ErosionSaltation one particle hitting another and being blown across the surface of the soil.25Suspension airborne soil. Ex. soil from Lubbock is found in Temple, Texas.

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Desertification: Degrading DrylandsAbout one-third of the worlds land has lost some of its productivity because of drought and human activities that reduce or degrade topsoil.Figure 13-1227Salinization and Waterlogging of Soils: A Downside of IrrigationExample of high evaporation, poor drainage, and severe salinization.White alkaline salts have displaced cops.Figure 13-14

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Salinization and WaterloggingRepeated irrigation can reduce crop yields by causing salt buildup in the soil and waterlogging of crop plants.Figure 13-1329SolutionsMore efficient irrigationBetter planning of farmlandsGenetic Engineering

Fig. 13-15, p. 281CleanupPreventionSoil SalinizationSolutionsReduce irrigationSwitch to salt-tolerant crops (such as barley, cotton, sugarbeet)Flush soil (expensive and wastes water)Stop growing crops for 25 yearsInstall underground drainage systems (expensive)31Figure 13.15Solutions: methods for preventing and cleaning up soil salinization. QUESTION: Which two of these solutions do you think are the most important?Erosion Control (see Miller pg. 282)Shelterbelts can reduce wind erosion. Long rows of trees are planted to partially block the wind. They can also help retain soil moisture, supply some wood for fuel, and provide habitats for birds.

32Minimum Tillage (conservation tillage) to disturb the soil as little as possible while planting crops.

Special tillers break up and loosen the subsurface soil without turning over the topsoil, previous crop residues, and any cover vegetation.

33Traditional Agriculture: Low Input PolycultureMany farmers in developing countries use low-input agriculture to grow a variety of crops on each plot of land (interplanting) through:Polyvarietal cultivation: planting several genetic varieties.Intercropping: two or more different crops grown at the same time in a plot.Agroforestry: crops and trees are grown together.Polyculture: different plants are planted together.

34SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATIONModern farm machinery can plant crops without disturbing soil (no-till and minimum tillage.Conservation-tillage farming:Increases crop yield.Raises soil carbon content.Lowers water use.Lowers pesticides.Uses less tractor fuel.35Contour Farming sloping your growing crops, etc. You run terraces parallel to the ground to stop soil from running down a steep slope. Plowing and planting crops in rows across, rather than up and down, the sloped contour of the land.

36Terracing (what you use for contour farming.) Dirt goes up to hold the dirt in place. Broad, nearly level terraces that run across the land contour. Helps to retain water for crops at each level and reduce soil erosion by controlling runoff.

37Strip Cropping a row crop such as corn alternates in strips with another crop that completely covers the soil, reducing erosion. It catches and reduces water runoff and helps prevent the spread of pests and plant diseases.38Cover Cropping (alley cropping) several crops are planted together in strips or alleys between trees and shrubs that can provide shade (which reduces water loss by evaporation) and helps to retain and slowly release soil moisture.

39Irrigation TechniquesConventional center-pivot irrigation- allows 80% of the water input to reach crops Gravity-flow irrigation- Valves that send water down irrigation ditches. Drip irrigation- Can raise water efficiency to 90-95% and reduce water use by 37-70%.Floodplain irrigation- allowing the natural floods to irrigate the crops. Soils in flood zones tend to be nutrient rich and fertile.40DefinitionHydroponics are growing plants in fertilized water.Hydroponics:Method of suspending plants in water and the solutions involved. Ex. cranberries are grown this way.41Costs of Hydroponics:It is labor-intensive and expensive.You can control the environment & grow plants where there is no soil; NASA is looking into this.Benefits:42THE GREEN REVOLUTION43THE GENE REVOLUTIONTo increase crop yields, we can mix the genes of similar types of organisms and mix the genes of different organisms.Artificial selection has been used for centuries to develop genetically improved varieties of crops.Genetic engineering develops improved strains at an exponential pace compared to artificial selection.Controversy has arisen over the use of genetically modified food (GMF).44

Mixing GenesGenetic engineering involves splicing a gene from one species and transplanting the DNA into another species.Figure 13-1945