2What determines the type of soil? Parent Material – the type of rocks naturally found in an areaQuartz sand based rocks create nutrient depleted soil that is not good for farmingSoil with calcium carbonate parent material will have plenty of calcium, a high pH and be good for farmingClimateneed non-freezing temps to encourage decomposition plus climate determines vegetation which provides the organic matter for soilTopography – geographical features of the areaSteep slopes will constantly erode leading to poor soilRiver deltas have seasonal flooding that deposit nutrients and silt which lead to good soilOrganismsOrganisms help churn soil mixing nutrients evenly plus they aid in decomposition and nutrient cyclingTimeIt takes a long time for soil to form, so in general older soils are better and more established, but it depends on the vegetation.Desert soil might be old, the lack of vegetation means it does not improve much with age
3Soil formation Rock is broken down over time by weathering Organisms live and die, adding nutrients and eventually organic matterRate: 1cm can take yearsOver time, distinct layers called horizons formA renewable resource, but a slow one
5Soil profile Made up of soil horizons Different textures and compositionsCan be observed by digging a soil pitMature soils have 3 or more horizons
6O-Horizon May or may not include the leaf litter layer Organic detritus (bits of leaves, twigs, etc) on top of a layer of partially decomposed organic matter (called humus)Soil is brown or black underneath litter
7A-HorizonTopsoilConsists of partially decomposed organic matter, inorganic minerals, and living organisms.dark brown or black usually = nutrient rich = good for farminggray, yellow or red = low organic matter = poor for farmingZone of biological activityA
8E horizon – not always present or noted Zone of leachingA zone present in acidic soils,either between the O and A horizon or below the A horizonalways above the B horizonNutrients and minerals move quickly through this layer are deposited in the B horizon
9B-Horizon Yellow = alum oxides Sub Soil Red = iron oxidesWhite = calcium carbonateSub SoilMostly inorganic – rich in Fe, Al, and humic compoundsNutrients leached down from A horizonAlmost no organic matterRoots may extend into this layer
10C-HorizonWeathered parent material. Broken rock fragments
12Soil MatrixSoil is a mixture of organic and inorganic materials such as air, water, plant and animal materials50% = inorganic and organic particles50% = open areas called pores
13What is in soil? Organic Inorganic Pores Decomposing material Minerals Leaf litterDead plants and animalsProvide nutrients!Living organismsBacteriaSoil-invertebratesDECOMPOSERSAll require oxygenInorganicMineralsMacronutrientsprimary – N, P,KSecondary – Ca, Mg, SMicronutrientsB,Cu, Fe, Cl, Mn, Mo, ZnRockPoresStore O2 and nitrogen gasMay fill with water and roots
14Soil Texture Textures Sand - biggest particles (0.05 – 2.00mm) Silt – ( mm)Clay – smallest components (less than .002mm)Determined by the % of each type of particleGritty = sandSmooth = siltSticky = clay
15Soil Texture Importance ImpactsToo sandy = rapid infiltration and nutrient lossToo much clay = no infiltration, too hard, roots suffocate, drown, or can’t penetrateToo silty = compact easily, crusty surfaceLoama mixture of sand - silt - clayBEST for farming!Promotes drainage while alsoretaining nutrients
16Porosity Permeability The percentage of open pore space in soil Silty soil holds water wellCoarse soil holds airPermeabilityThe rate at which water flows through soilDetermined by porosity and structure
17Soil pH The pH scale goes from zero to fourteen. pH correction The soil pH is a measurement of the acidity or alkalinity within the soil.Soil pH is the negative logarithm of the hydrogen ion concentration.The pH scale goes from zero to fourteen.< 7 = acidic7 = neutral> 7 = basicA pH of is best for most cropspH correctionToo acidicAdd lime to neutralizeMust be used with organic fertilizerToo BasicAdd sulfur which is converted to sulfuric acidVery SLOW
18Acidic soils Acidic soils Soil in California tends to be basic Hinder nutrient availabilityIncrease availability of toxic heavy metalsMajor problem for urban gardens in the northeast USIncrease pesticide runoffDecrease bacteria populations less nitrogen fixationSoil in California tends to be basicSoil in the northeastern US is more acidic
20A toxic white crust runs through irrigated fields in Grand Valley, Colorado: Moisture evaporating from the soil has drawn underground salt to the surface. To keep the salt from damaging the roots of their crops, farmers must add even more water.
21Thick, six-foot-long roots of sunflowers, side-by-side with the roots of assorted prairie grasses, delve deep into a plot of earth near Salina, Kansas. This soil has never been broken by a plow. These perennials have root systems that expand and strengthen year after year—unlike annual crops that demand much of the soil but provide little in return. Such growth not only helps prevent erosion but also serves as a water-storage system that enables the plants to survive during droughts.
22Virgin Prairie—Kansas, United States. Rancher Jim Duggan holds a stalk of big bluestem, one of the native grasses growing on 40 acres of his farmland that have never been plowed. "This land is the best there is," he says. "It's class-one river-bottom soil." Compared with tilled fields, the parcel has deeper, richer topsoil and soaks up more rain.
23Reclaimed Fields—Keita District, Niger. Mariama Abdoulaye feeds her family with millet she grows on once barren land. After severe droughts in the 1970s and ’80s, the UN Food and Agricultural Organization enlisted Abdoulaye and 10,000 other women to plant millions of trees. Tree roots block wind-driven erosion and help rain penetrate the earth.
24Rice Terrace—Yunnan Province, China. Perched on an earthen retaining wall, Zhu Minying holds cords used to bundle harvested rice. Soil here reflects human activities that began with reshaping hillsides into grand staircases of grain. Rice stubble left to decay in the field, manure, and fish raised in the paddy water, all add nutrients to Zhu's soil.
25Dry Land—Khanasser Valley, Syria. Farmers like Ismail Hassoun Hariri struggle to grow even hardy barley in this parched land. Soil and rock eroded from surrounding hills lie thick in the valley, but annual rainfall averages only nine inches. In some very dry years the barley crop fails to mature and can only be used to feed sheep and goats.
26After losing a foot of soil from parts of their Iowa corn farm, the Reed family changed the way they prepare fields for planting, to limit erosion. Cletus Reed, 80, hopes his grandson, Sam, will work these acres someday. "The land takes care of us as we care for it," he says.
27Tiny earthworks stipple bare slopes in China's Zizhou County, each intended to cradle a single sapling. Government mandated reforestation programs are intended to halt erosion, but many earlier efforts here in the Loess Plateau failed when newly planted trees died.
28Organically farmed soils (at left) have a more cohesive structure, which results in less silty runoff than found with conventionally farmed soils (at right). These samples come from the Farming Systems Trial at the Rodale Institute near Kutztown, Pennsylvania. For 28 years, a plot of land there has been managed organically: Researchers rotate crops regularly, grow cover crops in winter, and apply no chemical fertilizers or pesticides. Laboratory analysis shows that organically managed soils produce lots of glomalin, a gluey protein that helps earth hold its ground.