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1、ChemicalSoil Health for Organic ProductionCharles Mitchell, Auburn University Alisha Rupple, University of Arkansas Heather Friedrich, University of ArkansasSurface mineral layer of the earth that is mixed with organic matter (living and non-living) that serves as a growing media for land plantsComb
2、ination of biological, physical, and chemical processes, particular to regions and climatesWhat is soil?Agriculture / growing plants50% Pore Space25% Water-filled25% Air-filled45% Mineral Material5% Organic MatterThree Main Soil ComponentsSoil HealthPhysicalChemicalBiologicalOverlapping of the physi
3、cal, chemical, and biological propertiesGeneral picture of soils capacity to support plant growth without degradation (sustainability)PhysicalChemicalBiologicalProportion of sand, silt, and clay particlesThe ideal texture depends on which crop will be grown. Potatoes grow best in a sandy soil while
4、rice grows best in clay soil.Sand: good drainage, ease of cultivation, dries easily, nutrients lost to leachingClay: good water-holding capacity, high CEC, holds nutrients, easily compacted, poor drainageTextureCLAY CEC = lime)Cation exchange sites hold Ca2+, Mg2+ , K+, NH4+, and Na+ ions and reduce
5、 leachingCation exchange sites adsorb many metals (Cd2+, Zn2+, , Ni2+, , Pb2+, )that might be present in waste water. CEC and Soil Management-log H+; measure of acidity/alkalinity of soilSoils under field conditions vary from 3.5- 10.05.5-8.5: range for most cropsStrongly acidic soils- Al3+ and Mn2+
6、 at toxic level; microbial activity reduced; Ca2+, Mg2+ , and K+ limited; fungi favoredStrongly alkaline soils- Fe2+ , Zn2+ , Cu2+ , Mn2+, and P limited; salinity toxicity pHpH Effects on Nutrient AvailabilityPhysicalChemicalBiologicalRanges from 1-5% in most soilsLiving fraction: roots, microorgani
7、sms, soil faunaAlkaline soil favors bacteriaAcidic soil favors fungi, mites, collembolaNeutral soil favors earthworms, termitesNon-living fraction: surface litter, dead roots, microbial metabolites, humusGreatest concentration in the top 6 inchesSoil Organic MatterComponents of Soil OMImprove soil s
8、tructure by ingesting organic matter and soil and excreting stable aggregatesAerate and stir soil, which improves water infiltration and root penetrationEarthwormsGenerally live in top 2m of soil Unfavorable conditions include: sandy, salty, arid, or acid soils; temperature extremes; presence of mic
9、e, mites, moles, and millipedes; tillage.Decompose OMMineralize and recycle nutrientsFix nitrogenDetoxify pollutantsMaintain soil structureAble to suppress plant pestsParasitize and damage plantsSoil MicrobesUSDA-NRCS Soil Biology PrimerSoil bacterial colonization of POM (Active C fraction of SOM)*
10、* Microbes are concentrated on/near POM rather than distributed homogenously in soil *Haynes, 2005. Adv. Agron. 85:221-267.Important to maintain actively decomposing organic material in soilsDecomposition of plant residue to stable soil humusPlants and AnimalsDecomposable Organic ResiduesHeterotroph
11、ic BiomassSoil Humus (50-80% of OM)Soil SurfaceBiologically resistant organicsMicrobial productsNutrientsStabilizes particles together as aggregates, esp. in sandy and clay soilsDecreases bulk density, providing resistance to compaction and improved porosityImproves water infiltration and retention
12、Able to retain 20x its weight in waterImproves friability, allowing for better root penetrationEffect of OM on Physical PropertiesIncreases CECIncreases nutrient retentionForms stable, chelated complexes with Fe3+, Mn2+, Zn2+, Cu2+, and other cationsEffect of OM on Biological PropertiesProvides C so
13、urce and energy for soil microbesImproves microbial population and diversityDiverse, active microbial population less likely to support spread of plant pathogensEffect of OM on Chemical PropertiesProper use of tillageConventionally thought necessary for weed control, to incorporate OM, and allow roo
14、t growthDamages structure, lowers OM content and overall soil productivityDecreasing tillage improves soil quality and fertilityNo-till practices may initially decrease yields and increase fertility needsManagement of Soil OMProper management of OM is a major factor in sustainable production Maintai
15、n constant inputs of organic materials to replace loses from harvest/decompositionEncourage biodiversity of plant speciesManagement of Soil OMBob Kremer, USDA ARSUse cover cropsIncorporate crop residuesAvoid pests/diseases by crop rotation, proper timing of incorporation, or compost residue away fro
16、m fieldManagement of Soil OM33Maintenance of vegetative residues through cover cropping, refuge areas, buffer strips, etc not only restores organic matter but also provides habitats for natural insect predators of weed seedsOsage County, MOMicro-insect larva attacking Amaranthus (i.e., pigweed) seedIntegrate livestock Distribution of OM over landscape
