 soil fertility  ability of a soil to provide nutrients for plant growth  involves storage...

Download  Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

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Understanding Soil Chemistry

Understanding Soil ChemistryImportance of Soil FertilitySoil FertilityAbility of a soil to provide nutrients for plant growthInvolves storage and availability of nutrientsVital to a productive soilFertile soil is not necessarily a productive soilWhy?Poor Drainage, Insects, Drought, and other factors can limit production

Existing plant-soil relationships affect soil productivityExternal factors control plant growthAirTemperatureLightMechanical supportNutrientsWater Plants rely on soil to provide all these except lightImportance of Soil FertilityWater and air fill pore spaces in soilFactors that affect water relationships also affect soil airNutrient availability is influenced by soil and water balance and temperatureRoot growth is influenced by soil temperature as well as soil, water, and airImportance of Soil FertilityUnderstanding Soil ChemistrySoil ProductivityWhat is organic matter?Plant, animal, and microbial residuesVarying stages of decayAdequate levels of O.M. benefit soil by:Improving physical condition and tilthIncreases water infiltrationDecreases erosion lossSupplies plant nutrients

Role of organic MatterOrganic matter contains about 5% NN is not immediately availableDecomposition must occur firstFertilizer (inorganic) N is needed for non-legume plantsOrganic matter also provides soil with a variety of other mineral elements that plants need to be healthySome include: phosphorus, magnesium, calcium, sulfur, and othersRole of organic MatterRole of Soil DepthSoil DepthDepth of soil material favorable for plant root penetrationPlants need soil to be:DeepWell-drainedCorrect textureCorrect structureDeeper soils provide for more nutrient storageRoots can extend 3-6 feet or more when soil depth permitsRooting depth is affected by Physical barriersChemical barriersHigh water tablesHardpans, Shale beds, Gravely Layers and accumulations of salts are very hard to correctRole of Soil DepthRole of surface SlopeSurface slope is part of what?TopographyDetermines the amount of runoff and erosionAlso determines:Irrigation methodDrainageConservation practicesThe steeper the land the more management is neededMore labor and equipment costsAt certain slopes, soil is no longer suitable for row crops.What are some row crops?Potential productivity is largely determined by ease of erosion along with percent of slopeRole of surface SlopeRole of Soil OrganismsMany different organisms live in the soilUsually in the first foot of top soilDepend on organic matter for foodFactors that affect the amount soil organisms:MoistureTemperatureAerationNutrient supplySoil pHCrop that is being grown

Some of the microscopic organisms cause many favorable soil reactionsdecay of plant and animal residuesspeed nutrient cycling.Other reactions can be injuriousdevelopment of organisms that cause plant and animal diseasesRole of Soil OrganismsRole of Nutrient BalanceNutrient balance is a vital concept in soil fertility and crop productionNitrogen is the first limiting nutrient in non-legumesWithout adequate amounts of the other nutrients, N cannot do its bestAs Nitrogen fertilization raises yields, the crop demands more of the other nutrientsUnderstanding Soil ChemistrySoil pHSoil pHThe measure of acidity or alkalinity of the soilpH is determined by the concentration of hydrogen ions(H+) and hydroxyl ions(OH-) in the soil solutionPure water has an equal number of H+ and OH-

Soil phAnother term for alkaline is basic

Acid = high in H+Basic = high in OH-

A soil with a pH of 6.0 has 10 times as much active H+ than neutral

Soil phPlants will not thrive in soil that is too acid or too alkalineThe soil pH directly affects the availability of mineral nutrientsExampleLow pH: phosphates may be bound chemically in the soil so plants are unable to access themAlso means that nitrate production in the soil is reducedSoil PHSeveral factors influence Soil pHOrganic matterParent materialRainfallleachingForest vs. grasslandHarvesting cropsLegumesSoil depthFertilizer applicationFlooding

Soil phHow to measure soil pHIndicator dyespH meterWhich do you think is more accurate?

The meter

If our soils pH was too acidic what would we add to amend it?LimeLime requirementSoil pH is not the determining factor on how much lime to addWhat else do we need to consider?Texture of soilAmount of organic matterThe amount of clay and organic matter in a soil will determine the ability of a soil to resist pH changeMore clay/organic matter = more pH bufferingThe process is very complexExample: Al and waterLime requirementLime requirementAmount of Ag limestone needed to establish the desired pH range for the cropping system being usedLime reduces soil acidityLook at Al and water exampleUses Ca ionSoil will become more and more acidic if a liming program is not followed

We do not apply lime to soils here in Northern Utah very often Why?Lime RequirementIn the case of high pHLowering pH is not usually economicalThese are generally high in saltsFind plants that tolerate high salt levelsCation Exchange CapacityAs soils formSome particles are broken down into extremely small particlesChemical weathering breaks them down until they cannot be seen with the naked eyeThe smallest are called colloids

Colloids are responsible for chemical reactivity in soilEach colloid has a negative(-) chargeCation Exchange CapacityThe neg. charge will attract positively(+) charged particlesWhat does that mean if they run into another negative?Cations: Positive ChargeAnions: Negative Charge

Colloids act like a magnet and holds cationsOther cations can take their placeThey are exchangeable

Cation Exchange CapacityCan a soil hold more cations than it has colloids?noWe need to know our soils CEC

Higher CEC = more cations can be heldDepends on clay and organic matterLots of clay = higher CECMore organic matter = higher CECCation Exchange CapacityLeaching is reduced by higher CEC

Knowing our CEC will help determine how much fertilizer to apply and how often


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