Soil & soil fertility

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Soil & soil fertility. Africa Soil Health Consortium 2014. Lecture 2: Introduction to soil and soil fertility. Objectives. Gain knowlegde on the principles underpinning ISFM practises Introduction to soil Soil texture Porosity Mineral fraction Organic matter Introduction to nutrients - PowerPoint PPT Presentation

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<ul><li><p>Soil &amp; soil fertilityAfrica Soil Health Consortium2014Lecture 2: Introduction to soil and soil fertility</p></li><li><p>ObjectivesGain knowlegde on the principles underpinning ISFM practises</p><p>Introduction to soilSoil texturePorosityMineral fractionOrganic matterIntroduction to nutrientsUnderstanding the function of nutrients in plant growthRecognizing nutrient deficienciesSoil fertilityUnderstanding the concept of soil fertilityIntroduction to soil fertility managementConservation agriculture &amp; organic agricultureMinimizing losses of added nutrients</p></li><li><p>SoilSoil solidsPore space+ soil fauna and floraPore space: -space for roots and micro-organisms-air for micro-organisms-water storageMineral fraction:Provides support to plant rootsSlowly releases nutrients into the soil solutionOrganic fraction:Soil organic matter (SOM)Key issue in soil fertility management</p></li><li><p>Pore spacePorosity: volume of the soil occupied by air and the soil solution</p><p>Porosity inWell-drained moist soil: sufficient moisture for plant growth and sufficient aeration for proper root functionDry soil: all pores are filled with air drought stressFlooded soil: pores are saturated with water roots cannot breathe and plants may die</p><p>Illustration adapted from Brady 1984, The nature and properties of soils, 9th edition.</p></li><li><p>Mineral fractionSand: 0.05 - 2.0 mmSilt: 0.002 - 0.05 mmClay: &lt; 0.002 mmIllustration adapted from: www.iconn.orgSiltClaySand</p></li><li><p>Mineral fraction</p></li><li><p>Mineral fractionThe finger test</p></li><li><p>Mineral fraction &amp; PorositySoil texture affectsPorosityWater holding capacityNutrient retention and supplyDrainageNutrient leachingIllustrations adapted from: http://wegc203116.uni-graz.at/meted/hydro/basic/Runoff/print_version/04-soilproperties.htm Infiltration Variations by Soil TextureSandSiltClay</p></li><li><p>Mineral fraction &amp; CECCations: positively charged ions (e.g. K+, NH4+)Cation exchange capacity (CEC): the maximum quantity of total cations that a soil is capable of holding. Clay fraction and SOM: Small particle size Large negatively charged surface area More positions to hold cations High CEC </p><p>Illistration adapted from: http://www.spectrumanalytic.com/support/library/ff/CEC_BpH_and_percent_sat.htm</p></li><li><p>Mineral fraction &amp; CECCEC depends onClay contentType of clay mineralSOM contentSoil pH</p><p>Clay minerals differ in structure1:1 clay minerals CEC varies with soil pH Found in most upland soils in SSA2:1 clay minerals Large inherent CEC capacity Found in fertile lowland soils</p><p>Illustration adapted from Lory Structure of Clays www.soilsurveys.org</p></li><li><p>Organic fraction: SOMSOM: plant and animal residues, in various stages of decompisition Picture: http://www.guiadejardineria.com/jardineria/suelos-y-abonos/page/7/</p></li><li><p>Organic fraction: SOMContains essential plant nutrientsImproves the soils Cation Exchange Capacity Improves the soils water-holding capacity (SOM can hold up to five times its own weight in water!)Improves water infiltration Buffers soil pHBinds with toxic elements in the soilImproves soil structure by stimulating activity of soil flora and faunaRegulates the rates and amounts of nutrients released for plant uptake</p><p> SOM is a key issue in soil fertility management!</p><p>Illustration adapted from: http://www.tekura.school.nz/departments/horticulture/ht106_p4.html</p></li><li><p>Soil analysisSoil test: chemical method for estimating the nutrient-supplying power of a soilLaboratory needs a representative composite sample of 0.5 kg</p><p>Be aware of heterogeneity within fields when sampling!</p></li><li><p>Guidelines for soil samplingTake a representative sample!!!</p><p>Check the area to be sampled for notable features (e.g. slope, soil types, vegetation, drainage).Draw a sketch map, and identify and mark the location of sampling sites.Take soil samples with a soil auger at the sampling depth (0-20 cm or 20-40 cm).Take 10-35 sub-samples per site, the number depending on the size and heterogeneity of the field. Combine the sub-samples to one composite per site and mix thoroughly. If necessary, reduce sample weight by sub-dividingLabel the sample of soil properly.Air-dry the sample and when dry, store it, properly labelled, in a plastic bag or a glass bottle for further analyses.</p></li><li><p>NutrientsMacronutrients: at least 0.1% of plant dry matter per macronutrient</p><p>Nitrogen (N): Amino acid/Protein formationPhotosynthesis</p><p>Phosphorus (P):Energy storage/transferRoot growthCrop maturityStraw strengthDisease resistanceNeeded in large amounts during plant growthRequired for N2-fixation by legumes</p><p>Potassium (K):Plant turgor pressure maintenanceAccumulation and transport of the products of plant metabolismDisease resistanceRequired for N2-fixation by legumes</p><p>Sulphur (S):Part of amino acids (protein formation)Synthesis of chlorophyll and some vitaminsRequired for N2-fixation by legumes</p><p>Magnesium (Mg):PhotosynthesisActivates enzymesCarbohydrate transport</p><p>Calcium (Ca):Cell growth and walls Activates enzymes (protein formation and carbohydrate transfer)Essential in calcicole plants (e.g. Groundnut) for seed production.Influences water movement, cell growth and divisionRequired for uptake of N and other minerals </p><p>Poor mobilityVery mobileVery mobileVery mobileVery mobileQuite poor mobilityVery mobileVery mobilePoor mobilityQuite mobileQuite poor mobilityMedium mobility</p></li><li><p>Nutrients</p><p>Micronutrients: less than 0.1% of plant dry matter</p><p>Iron (Fe):PhotosyntheissRespiration</p><p>Manganese (Mn):PhotosynthesisEnzyme function</p><p>Boron (B):Development/growth of new cells</p><p>Zinc (Zn):Nucleic acid synthesis and enzyme activationCopper (Cu):Chlorophyll formationSeed formationProtein synthesis</p><p>Molybdenum (Mo):Protein synthesis and N uptakeN2-fixation by legumes</p><p>Chlorine (Cl):Movement of water and solutesNutrient uptakePhotosynthesisEarly crop maturityDisease control</p><p>Cobalt (Co):N2-fixation by legumes</p><p>Nickel (Ni):Required for enzyme urease</p><p>Sodium (Na):Water movement and balance of minerals</p><p>Silicon (Si)Cell wallsProtection against piercing by sucking insectsLeaf presentationHeat and drought tolerance</p></li><li><p>Nutrient deficiencyHealthyN-deficientP-deficientK-deficientDiseased</p></li><li><p>Nutrient deficiencies</p></li><li><p>Nutrient deficiency: exercise</p></li><li><p>Nutrient deficiency: exerciseP-deficientStunted growthPurplish colouringK-deficientBrowning of leaf edges</p></li><li><p>Nutrient uptake</p><p>NutrientPlants take upN NO3-, NH4+PH2PO4- , HPO42-KK+SSO42-MgMg2+CaCa2+FeFe2+ and Fe3+MnMn2+ and Mn3+B(BO3)3-ZnZn2+CuCu2+MoMo42+ClCl-CoCo2+NiNi2+NaNa+Si(SiO4)4-</p></li><li><p>Nutrient availabilityReadily available- Nutrients from soluble fertilizers (e.g. KCL), readily mineralized SOM, nutrients held on the edges of soil particles, and in the soil solution</p><p>Slowly available- Nutrients in organic form, such as plant residues and organic manures (particularly with a high C/N ratio), slowly soluble mineral fertilizers (e.g. Phosphate rock) and the SOM fraction resistant to mineralization</p><p>Not available- Nutrients contained in rocks, or adsorbed on soil particles</p></li><li><p>Soil fertilityThe capacity of soil to supply sufficient quantities and proportions of essential chemical elements (nutrients) and water required for optimal growth of specified plants as governed by the soils chemical, physical and biological attributes.</p><p>Chemical elements for plant nutritionAdequate soil volume for plant root developmentWater and air for root development and growthAnchorage for the plant structure</p><p>Inherent DynamicSoil textureSoil organic matter (SOM)DepthNutrient- and water-holding capacityParent material Soil structure</p></li><li><p>Soil fertility management practicesNutrient deficiencies prevent a good harvestNutrient deficiencies can be expressed during plant growth</p><p>Use mineral (fertilizer) or organic (manure, crop residues) to supply nutrientsUse special fertilizer blends containing micronutrients or manure in case of micronutrient deficiencies</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingHealthyN-deficientP-deficientK-deficient</p></li><li><p>Soil fertility management practicesAcidity is caused byinherent soil propertiesacidity inducing management (e.g. long-term use of ammonium based fertilizer)Acid soils have high exchangeable Al (Al toxicity)</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingLimeIncreases pHPrevents Al and Mn toxicity in acidic soils (pH </p></li><li><p>Soil fertility management practicesCompaction sub-surface soil barrier to root growthBreak hardpans by ploughing or chisel ploughing to 30 cm depth</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingIllustration adapted from: http://locallygerminated.wordpress.com/Surface crust</p></li><li><p>Soil fertility management practicesCapture more rainfall in areas that are prone to droughtHarvesting additional water (e.g. Za)Promoting infiltration by coversing the soil surface with mulchLabour intensiveCorrecting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingZa pits in NigerMulching of bananas, western UgandaPictures: fao.org</p><p>Lydia Wairegi - revised this from 'are' to 'include' in notes</p></li><li><p>Soil fertility management practicesProne to erosion: fields on steep slopes, or on gentle slopes with course-textured top soilMeasures: live barriers (e.g. grass strips), teracces, surface mulch</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingBunds on sloping land in Burundi</p></li><li><p>Soil fertility management practicesGood seedbed preparation improves germination and reduces the chance for diseases</p><p>A delay in planting date often affects yield negativelyPlanting time is important especially when the growing season is short</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercropping</p></li><li><p>Soil fertility management practicesCrops compete for nutrients, water and lightUse a correct planting density, adjusted to crop type and the environment. Consider the distance between rows, between plants within rows and the number of plants per planting hole.</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercropping</p><p>CropOptimal rainfallPoor rainfallDensityBetween rowsWithin rowsDensityBetween rowsWithin rows000 Plants/hacmcm000 Plants/hacmCmBeans (common)20050101335015Maize447530379030Soybean444455333605</p></li><li><p>Soil fertility management practicesUse viable seed (at least 80% germination)Plant seeds at the correct depth and insert cuttings at correct anglePlant more seeds than required for optimal plant density. </p><p>Weeds compete with crops for nutrients, water and light.Timely removal of weeds is essentialWeed before top dressing crop with fertilizer</p><p>Control pests and diseases at specific growth stages</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingDelayed weeding reduces the crop response to fertilizer</p></li><li><p>Soil fertility management practicesIntercropping arrangements: take into account specific growth features and needs of individual crops to minimize intercrop competition.Examples: delayed planting of one intercrop, adjusting spacing, strip intercropping</p><p>Correcting nutrient deficienciesSoil acidity correctionBreaking hardpansWater harvestingErosion controlLand preparationPlanting dateSpacingPlanting practicesWeedingPest and disease managementIntercroppingMaize-pigeonpeaMaize-cassavaCassava-soybean</p></li><li><p>Conservation agriculture (CA)Basic principlesSoil disturbance is minimized by reduced or zero-tillageUse of at least 30% soil cover (mulch or cover crops)Use of crop rotations/associations</p><p>AdvantagesRapid planting of large areasReduction of soil erosionPitfallsCompeting uses of crop residues needed for mulchYields may decrease on the short-term (the increase often comes on the longer-term)Increased weed pressure caused by reduced tillageFull CA requires a fundamental change in the farming system. This may not be practical or enomic for the farmerPossible decrease in agronomic efficiency of fertilizer use</p><p>Lydia Wairegi - revised 'agriculture'Lydia Wairegi - 'thus is underpinned' to 'this is underpinned'</p></li><li><p>Organic agricultureReliance on organic resources to provide nutrients to sustain soil fertility and produce economic crop yields</p><p>However, mineral fertilizers are an essential component in sustainable agriculture in SSASoil nutrients stocks in large parts of SSA have already become depleted and require replenishmentOrganic resources are not available in large enough quantities to replenish and sustain nutrient stocks in the soilLarge and economic responses to mineral fertilizer are obtained in many parts of SSAOrganic resources are bulky and their management is labour intensive</p><p>ISFM: use of mineral fertilizer in combination with organic resources. The combination provides the greatest benefits!</p></li><li><p>Minimizing losses of added nutrientsLosses of nutrients into the environmentDepletion of nutrients in farming systemsEutrophication in case of excessive mineral fertilizer use (not common in SSA)</p><p>Losses throughHarvesting crops recyclingWater and wind erosionLeachingVolatilization</p><p>Nitrogen is the most susceptible to lossesVery mobile, can be lost through different waysNO3- is susceptible to leaching. </p></li><li><p>Losses: Water and wind erosion10 kg N/ha, 2 kg P/ha and 6 kg K/ha lost in low-input production systems in SSA</p><p>Measures: grass strips, stone rows, mulch layer, soil preparation methods (e.g. Za), improving SOM</p><p>Tied rigdesBunds on sloping land in Burundi</p></li><li><p>Losses: LeachingProblematic in high rainfall areas and coarse-textured sandy soils (&gt;35% sand)Mainly NO3- and exchangeable bases (K and Mg) percolate beyond the reach of crop roots</p><p>Measures: Improving soil structure to promote good root development for increased accessibility of nutrients Growing annual crops in association with trees, which can pump water and nutrients from deeper layers</p></li><li><p>Losses: VolatilizationDenitrification of NO3- NO3- N2O and N2 (gasses) Occurs under anaerobic conditions Measures: improved soil drainage and maintain a good soil structure to avoid anaerobic growing conditions</p><p>Volatilization of NH3 in alkaline soils (high pH)Measures: deep placement of N-fertilizers</p><p>Volatilization of NH3 during storage and handling of manureMeasures: use anaerobic storage pits</p></li><li><p>SummaryPorosityCECTextureSoil organic matterNutrientsFunctions...</p></li></ul>

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