Bulk Density (BD) = Dry soil (g) / Dry Vol (cm3)Undisturbed = .8 – 1.2Compacted = 1.4 – 1.6Severe = 1.6 – 2.0+ (2.2 = concrete)Increases with depth due to gravity and weightSoil Porosity (SP) = [wet (g) – Dry (g) / soil vol (cm3)] x100Sand >25%Silt >35%Clay >45%Number of grains increases pore spaces meaning more water can be heldClay = hold more water bc finer particlesAgriculture and Environmental DegradationSoil erosion/sediment transport and deposit: top soil washed away with water because there is no ground coverFertilizer and pesticide pollutionDeforestationDesertificationGrazing INCREASES biodiversity in grasslandManure adds organic material, spreads seedsGraze on invasive speciesModerate disturbance  most biodiversityAquifer degradation: From fertilizer/pesticide pollutionSalinization: Pure water evaporates, salt left behindCentral Valley: Crops in arid areas = importing massive amounts of salts and water to irrigateMost subsidence (collapse of pore spaces) from over-pumping of ground waterCant get the pore spaces backDeep aquifer that is being pumped from, with another aquifer on top, separated only by a layer of clayWater table of shallow aquifer rises up, bringing deep salts with it, contaminating cropsCome farmers put tiles under their crops to drain water to be “someone else’s problem”Central Valley  wildlife refuge  kills many cows and birdsShut off drainContaminant build-up: solved with periodic floodingLoss of (soil) biodiversityPlowing the soilNothing in nature is comparable to a plowBreaks down the nutrients fasterGeorge Perkins Marsh: grew up in Vermont, 1864Compared deforestation with the fall of the Roman Empire“Environmental Pioneer”Soil can be productive without plowing, BUTcheaper to plowNo-till has more weedsEnvironmental Effects of AgricultureGlobal soil damage and soil lossLose soil from tilling (especially on a slope)1 mm soil lost per yearNo-till results in natural erosion rate (much lower)Soil FertilityCapacity of soil to provide nutrients for plant growthDependent onSize of the soil particlesSoil BiodiversityDamage from sunlightRemoval of organic matter – when we eat crops, our “organic waste” does not go back onto the cropsClimate changeAdd FertilizerAnimal ManureIncreases density of soil, helps them hold waterImprove chem/phys characteriestics of the soilUnder intense agriculture, not enough nutrientsChemical/artificial fertilizerIncreased production in the early 20th centuryHumans can fix nitrogen twice as fast as naturePhosphorus – comes from rocks in mines and bird poopNauru (island near Guam)Mined phosphorus and was the wealthiest soverieign country in 1960sDid not restore the land after they mined it  only the outskirts of the island is habitableHealth problems, country’s trust got misused  poorWith climate change, sea level rises  people cant live hereReducing soil erosionMulticropping: difficult because intercropped, more expensiveDon’t plow as often, terracing, crop rotation, no-till agriculture*Contour plowing – carries soil/water down when it rainsGMO’sMost common: corn, canola, soybean, cotton seed oilNeed to make crops disease resistant, mainly because of monocroppingResistant to herbicides, disease, cold, drought, salinityCONS: transferring genes, unknown health impacts, harm to organisms, economic concerns (some farmers report that GM crops have less yield than non GM crops), reduce pesticide effectivenessWREI Ch 6SSM Ch7Soil Management 03/07/2013Bulk Density (BD) = Dry soil (g) / Dry Vol (cm3)-Undisturbed = .8 – 1.2-Compacted = 1.4 – 1.6-Severe = 1.6 – 2.0+ (2.2 = concrete)-Increases with depth due to gravity and weight Soil Porosity (SP) = [wet (g) – Dry (g) / soil vol (cm3)] x100-Sand >25%-Silt >35%-Clay >45%-Number of grains increases pore spaces meaning more water can be heldoClay = hold more water bc finer particlesAgriculture and Environmental Degradation -Soil erosion/sediment transport and deposit: top soil washed away with water because there is no ground cover -Fertilizer and pesticide pollution-Deforestation-DesertificationoGrazing INCREASES biodiversity in grassland Manure adds organic material, spreads seedsGraze on invasive species Moderate disturbance  most biodiversity -Aquifer degradation: From fertilizer/pesticide pollution-Salinization: Pure water evaporates, salt left behind oCentral Valley: Crops in arid areas = importing massive amounts of salts and water to irrigate Most subsidence (collapse of pore spaces) from over-pumping of ground waterCant get the pore spaces backDeep aquifer that is being pumped from, with another aquifer on top, separated only by a layer of clay Water table of shallow aquifer rises up, bringing deep salts with it, contaminating crops Come farmers put tiles under their crops to drain water to be “someone else’s problem”Central Valley  wildlife refuge  kills many cowsand birds Shut off drain -Contaminant build-up: solved with periodic flooding -Loss of (soil) biodiversity Plowing the soil -Nothing in nature is comparable to a plow -Breaks down the nutrients faster-George Perkins Marsh: grew up in Vermont, 1864oCompared deforestation with the fall of the Roman Empire o“Environmental Pioneer”-Soil can be productive without plowing, BUT ocheaper to plowoNo-till has more weeds Environmental Effects of Agriculture -Global soil damage and soil loss-Lose soil from tilling (especially on a slope)-1 mm soil lost per yearoNo-till results in natural erosion rate (much lower) Soil Fertility -Capacity of soil to provide nutrients for plant growth-Dependent onoSize of the soil particles oSoil BiodiversityoDamage from sunlight oRemoval of organic matter – when we eat crops, our “organic waste” does not go back onto the cropsoClimate change-Add FertilizeroAnimal ManureIncreases density of soil, helps them hold waterImprove chem/phys characteriestics of the soilUnder intense agriculture, not enough nutrients oChemical/artificial fertilizer Increased production in the early 20th centuryHumans can fix nitrogen twice as fast as nature Phosphorus – comes from rocks in mines and bird poop-Nauru (island near Guam)oMined phosphorus and was the wealthiest soverieign country in 1960soDid not restore the land after they mined it  only the outskirts of the island is habitableoHealth problems, country’s