Organic Matter

UBC Farm Soil Workshop SeriesClass 2: Soil Organic Matter, Cover Cropping, and Related Management Strategies

Chris Thoreau February 18, 2012Todays OutlineWhat is Organic Matter?Organic Matter Roles in SoilCharacteristics and Types of OMOMs Effects on TextureSource of Organic MatterIncorporating OM into SoilCover Cropping and OM

What is Organic Matter?Organic Matter Roles in SoilCharacteristics and Types of OMOMs Effects on TextureSource of Organic MatterIncorporating OM into SoilCover Cropping and OM2Organic MatterSoil organic matter is the most important physical component of a healthy soil

Organic matter brings life to soils

It changes the characteristics of different textured soils without changing the texture itselfSoil organic matter is the most important physical component of a healthy soil

Organic matter brings life to soils

It changes the characteristics of different textured soils without changing the texture itself

3Organic MatterSoil organic materials are made up of:Dead and decaying plants or animalsAnimal manuresProcessed food by-products

Materials decomposed to different stages exist simultaneously

Manure, compost, and fresh plant debris are common OM additions to soil

Soil organic materials are made up of:Dead and decaying plants or animalsAnimal manuresProcessed food by-products

Materials decomposed to different stages exist simultaneously

Manure, compost, and fresh plant debris are common OM additions to soil

4Organic MatterOrganic matters role in soil:Holds soil particles together; stabilizes soilReduces erosion riskIncreases soils water holding and releasing abilityStores and supplies nutrients for plants & microbesMinimizes soil compaction especially in clay soilCarbon sinkAmeliorates the effect of environmental pollutantsImmobilizes them; reduces leachingOrganic matters role in soil:Holds soil particles together; stabilizes soilReduces erosion riskIncreases soils water holding and releasing abilityStores and supplies nutrients for plants & microbesMinimizes soil compaction especially in clay soilCarbon sinkAmeliorates the effect of environmental pollutantsImmobilizes them; reduces leaching5Organic MatterOrganic matter

Usually 5-8% of soil; 30% or more in org. soils.

12 20% or more desired in organic growing systems

Organic matter

Usually 5-8% of soil; 30% or more in org. soils.

12 20% or more desired in organic growing systems6Organic MatterSoil Organic Matter CharacteristicsHigh Cation & Anion Exchange Capacity (CEC)Soils ability to hold + and - charged nutrientsHigh in CarbonBuffer against pH changes in soilC:N ratio - indicator of Nitrogen (N) availabilityNutrient concentration and ratios variableParticle density: 900-1300 kg/m3Bulk density: 180-200 kg/m3 - 130 kg/m3Holds water better than mineral soils

Soil Organic Matter CharacteristicsHigh Cation & Anion Exchange Capacity (CEC)Soils ability to hold + and - charged nutrientsHigh in CarbonBuffer against pH changes in soilC:N ratio - indicator of Nitrogen (N) availabilityNutrient concentration and ratios variableParticle density: 900-1300 kg/m3Bulk density: 180-200 kg/m3 - 130 kg/m3Holds water better than mineral soils7Organic MatterCompost Characteristics: Carboxyl and Hydroxyl Groups

Go over CEC and stuff later; see lecture 17 for link to pH and CEC also talk about DDL and diffusion

8Organic MatterTwo Types of Organic Matter

Non-humicPrimary components from fresh animal and plant wasteEasily decomposed by microbes (when present)Comprise 20-30% of Soil OMDecompose to:Carbohydrates (several types)Amino AcidsLipidsLignin Very resistant to decayOther compounds

Two Types of Organic Matter

Non-humicPrimary components from fresh animal and plant wasteEasily decomposed by microbes (when present)Comprise 20-30% of Soil OMDecompose to:Carbohydrates (several types)Amino AcidsLipidsLignin Very resistant to decayOther compounds

9Organic MatterTwo Types of Organic Matter

HumicBiochemical decomposition of non-humic materialsResistant to further decompositionAccumulate in soilDark in colour give soil dark characteristic60-80% of soil OM3 types:Humins:larger particles; low number of carboxyl groups; inactive.Humic acids: smaller than humins (approximately colloid-sized); more carboxyl groups than humins.Fulvic acids:smallest humic substances; large number of carboxyl groups; most active among humic substances.

Two Types of Organic Matter

HumicBiochemical decomposition of non-humic materialsResistant to further decompositionAccumulate in soilDark in colour give soil dark characteristic60-80% of soil OM3 types:Humins:larger particles; low number of carboxyl groups; inactive.Humic acids: smaller than humins (approximately colloid-sized); more carboxyl groups than humins.Fulvic acids:smallest humic substances; large number of carboxyl groups; most active among humic substances.10Organic Matter

Organic MatterLiving MaterialDies onto soilHumicNon-Humic This process is driven by plant growth and biological decomposition; decomposition comes mostly from soil bacteria and fungiOrganic Matter and TextureWhat role does OM play in texture?

Organic Matter and TextureOrganic Matter and Sandy SoilSand does not hold water or nutrients, but drains very well (perhaps too well)Organic matter binds sandy soil particles together:Gives sand water-holding potential Acts as a nutrient storage and releaseStill allows for good drainagePromotes and sustains microbial life

This does not change the texture of a sandy soil, rather it changes the soils characteristicsOrganic Matter and Sandy SoilSand does not hold water or nutrients, but drains very well (perhaps too well)Organic matter binds sandy soil particles together:Gives sand water-holding potential Acts as a nutrient storage and releaseStill allows for good drainagePromotes and sustains microbial life

This does not change the texture of a sandy soil, rather it changes the soils characteristics

14Organic Matter and TextureOrganic Matter and Clay SoilClay soil holds water and nutrients very well, but is dense, poor draining, and susceptible to compactionOrganic matter separates clay particles:Increasing drainage abilityIncreasing air flow for roots and microbesReducing (but not eliminating) susceptibility to compaction

Organic Matter and Clay SoilClay soil holds water and nutrients very well, but is dense, poor draining, and susceptible to compactionOrganic matter separates clay particles:Increasing drainage abilityIncreasing air flow for roots and microbesReducing (but not eliminating) susceptibility to compaction

15Maintaining Soil Organic MatterSoil OM is decomposed by microbes - a process called mineralization

Once mineralized, soil organic matter can be carried into soil solution & absorbed by plants this depletes soil OM levels

It is our job as soil stewards to ensure our soil organic matter levels are maintained

Soil OM is decomposed by microbes - a process called mineralization

Once mineralized, soil organic matter can be carried into soil solution & absorbed by plants this depletes soil OM levels

It is our job as soil stewards to ensure our soil organic matter levels are maintained

16Maintaining Soil Organic MatterHigher temperatures, air, and nitrogen increase soil microbial activity and thus mineralizationWarmer temperature = more microbial activity = more growth in summer!Air is most often introduced through cultivationThis releases more nutrients, but also makes them susceptible to leachingNitrogen is needed by plants and microbes

Reducing cultivation slows down mineralizationWhat are benefits and costs of this?Higher temperatures, air, and nitrogen increase soil microbial activity and thus mineralizationWarmer temperature = more microbial activity = more growth in summer!Air is most often introduced through cultivationThis releases more nutrients, but also makes them susceptible to leachingNitrogen is needed by plants and microbes

Reducing cultivation slows down mineralizationWhat are benefits and costs of this?

17Maintaining Soil Organic MatterSlowing mineralization helps maintain organic matter levelsSlows down loss of OM

Slowing mineralization also slows the rate at which nutrients are available to plantsCan be disadvantage for fast-growing cropsCan be supplemented through foliar and liquid fertilizationSlowing mineralization helps maintain organic matter levelsSlows down loss of OM

Slowing mineralization also slows the rate at which nutrients are available to plantsCan be disadvantage for fast-growing cropsCan be supplemented through foliar and liquid fertilization

18Introducing Organic Matter to SoilHow and when we use organic matter, and what type of OM we use, depends on many factorsWhat organic materials are readily available?How close are those materials to our farm?What is our budget?How big is our space?How long is our growing season?What are current soil OM levels?

How and when we use organic matter, and what type of OM we use, depends on many factorsWhat organic materials are readily available?How close are those materials to our farm?What is our budget?How big is our space?How long is our growing season?What are current soil OM levels?

19Introducing Organic Matter to SoilGreat Urban Sources of OM:Fallen leavesBe careful of contaminantsGrass Clippings (pesticide free)Coffee grounds (acidic)Okara (tofu bi-product)Horse Manure

Great Urban Sources of OM:Fallen leavesBe careful of contaminantsGrass Clippings (pesticide free)Coffee grounds (acidic)Okara (tofu bi-product)Horse Manure20Introducing Organic Matter to SoilGreat Rural Sources of OM:Horse, cow, or chicken manureStrawSpoiled hayFallen leavesGreat Rural Sources of OM:Horse, cow, or chicken manureStrawSpoiled hayFallen leaves21Introducing Organic Matter to SoilWe can introduce OM to soil with:Crop growthAdditions of compostAdditions of fresh or decomposed manureAdditions of fresh or dried plant materialsMulching and Sheet MulchingCover croppingWe can introduce OM to soil with:Crop growthAdditions of compostAdditions of fresh or decomposed manureAdditions of fresh or dried plant materialsMulching and Sheet MulchingCover cropping

22Introducing Organic Matter to Soil1. Crop GrowthPlants add OM to soil from debris drop and root sloughingRoot sloughing adds OM to soil at lower depths without disturbing the soil

1. Crop GrowthPlants add OM to soil from debris drop and root sloughingRoot sloughing adds OM to soil at lower depths without disturbing the soil23Introducing Organic Matter to Soil

Introducing Organic Matter to Soil2. Compost AdditionsCompost nutrients are available to plants quicklyGreat addition at start of seasonDig into soilMulch soilCovering seeded rowsUse for transplanting and transplant mixesDouble diggingUse throughout growing seasonSide dress plantsContinue mulchingCompost tea

2. Compost AdditionsCompost nutrients are available to plants quicklyGreat addition at start of seasonDig into soilMulch soilCovering seeded rowsUse for transplanting and transplant mixesDouble diggingUse throughout growing seasonSide dress plantsContinue mulchingCompost tea25Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil3. Manure AdditionsCan be raw or decomposedRaw manure cannot be applied in winterRaw may be better side dressing if too much in soil can kill plantsDecomposed or rotted manure can be used like compostRaw manure is also a great compost activatorCan also make manure teas for foliar feeds

3. Manure AdditionsCan be raw or decomposedRaw manure cannot be applied in winterRaw may be better side dressing if too much in soil can kill plantsDecomposed or rotted manure can be used like compostRaw manure is also a great compost activatorCan also make manure teas for foliar feeds29Introducing Organic Matter to Soil4. Mulching: Additions of plant debris to the soil surfacePlant Trimming MulchStraw or other high carbon materialsCompost/Leaf MulchingSheet Mulching

4. Mulching: Additions of plant debris to the soil surfacePlant Trimming MulchStraw or other high carbon materialsCompost/Leaf MulchingSheet Mulching

30Introducing Organic Matter to SoilA Word or Two on Mulches:Addition of OM to soil at surfaceSlowly incorporated into soil by macro-organismsCan be incorporated by cultivationCan be any type of OM or even syntheticReduce soil evaporationReduce impact of rain on soil aggregatesRegulate soil temperaturePromotes biological activity near soil surfaceKeep away from base of plants

A Word or Two on Mulches:Addition of OM to soil at surfaceSlowly incorporated into soil by macro-organismsCan be incorporated by cultivationCan be any type of OM or even syntheticReduce soil evaporationReduce impact of rain on soil aggregatesRegulate soil temperaturePromotes biological activity near soil surfaceKeep away from base of plants

31

Introducing Organic Matter to Soil1. Plant Trimming MulchWhen trimming leaves off plants they can be dropped onto the soil surface as a mulchEasier than moving to compost binDo not use diseased leaves!

1. Plant Trimming MulchWhen trimming leaves off plants they can be dropped onto the soil surface as a mulchEasier than moving to compost binDo not use diseased leaves!

32

Introducing Organic Matter to Soil2. Straw and High Carbon MaterialsGood for long season crops (e.g., garlic, kales)Can be reusedAlso used for perennialsSawdust and blueberriesWait until very decomposed if incorporating into soil to maintain proper C:N ratio2. Straw and High Carbon MaterialsGood for long season crops (e.g., garlic, kales)Can be reusedAlso used for perennialsSawdust and blueberriesWait until very decomposed if incorporating into soil to maintain proper C:N ratio

33Introducing Organic Matter to Soil3. Compost/Leaf Mulching

Compost is a great mulch and should be used frequentlyNutrients leach into soil when watering

Leaf MulchCan often be acquired easily and for freeTree leaves have good nutrient profileLeaf mold (aged leaves) good for mulch and incorporating into soilCan be reused3. Compost/Leaf Mulching

Compost is a great mulch and should be used frequentlyNutrients leach into soil when watering

Leaf MulchCan often be acquired easily and for freeTree leaves have good nutrient profileLeaf mold (aged leaves) good for mulch and incorporating into soilCan be reused

34Introducing Organic Matter to Soil4. Sheet MulchingPermaculture folks love to sheet mulch!Great for: Improving poor, compacted soils with additions of OMQuickly adding life & nutrients to depleted soilReusing urban waste productsSuppressing noxious weed growth

Sheet mulching can be done anytime, but spring and summer are best

4. Sheet MulchingPermaculture folks love to sheet mulch!Great for: Improving poor, compacted soils with additions of OMQuickly adding life & nutrients to depleted soilReusing urban waste productsSuppressing noxious weed growth

Sheet mulching can be done anytime, but spring and summer are best35Introducing Organic Matter to SoilSheet Mulching:Alternating layers of carbon and nitrogen materialsOften starting with thick layers of cardboard or newspaperFresh manure or other high N materials at bottom helps suppress and decompose unwanted plant growthTopped with leaves or compostGiven lots of water!Can plant into soil pockets in new mulch

Sheet Mulching:Alternating layers of carbon and nitrogen materialsOften starting with thick layers of cardboard or newspaperFresh manure or other high N materials at bottom helps suppress and decompose unwanted plant growthTopped with leaves or compostGiven lots of water!Can plant into soil pockets in new mulch36Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to Soil

Introducing Organic Matter to SoilSynthetic Mulches:

Introducing Organic Matter to Soil6. Cover CroppingThe practice of growing a crop for the main purpose of improving soil qualityUsually not harvested for saleCan be planted at anytime of the year, but usually overwinter on the coast

6. Cover CroppingThe practice of growing a crop for the main purpose of improving soil qualityUsually not harvested for saleCan be planted at anytime of the year, but usually overwinter on the coast47Introducing Organic Matter to SoilCover Crops can be used to:Increase organic matter content of soilFix atmospheric nitrogenProtect soil from impact of rainSuppress weedsSuppress insect pestsProvide pollen for beesIncrease crop diversityCover Crops can be used to:Increase organic matter content of soilFix atmospheric nitrogenProtect soil from impact of rainSuppress weedsSuppress insect pestsProvide pollen for beesIncrease crop diversity

48Introducing Organic Matter to SoilIncreasing organic matter contentGrowing organic matter is one of the easiest ways to increase it in our soilImportant in rural and isolated areasImportant in closing the farm loopImporting seeds for cover crops is easier than importing organic matterCover crops contribute OM through growth above and below the soilCapture and store nitrogen in leavesIncreasing organic matter contentGrowing organic matter is one of the easiest ways to increase it in our soilImportant in rural and isolated areasImportant in closing the farm loopImporting seeds for cover crops is easier than importing organic matterCover crops contribute OM through growth above and below the soilCapture and store nitrogen in leaves49Introducing Organic Matter to SoilCrops for increasing OM:Winter Rye and WheatLeaf and root growthBuckwheat (spring and summer)Also accumulates PhosphorusOats (fall)Winter kills as mulchSunflowers (summer)Phacelia (summer)Also great for attracting beneficial insectsCalendula Pretty, too1Leafy Greens Tasty, too!Squash Lots of OM!

Crops for increasing OM:Winter Rye and WheatLeaf and root growthBuckwheat (spring and summer)Also accumulates PhosphorusOats (fall)Winter kills as mulchSunflowers (summer)Phacelia (summer)Also great for attracting beneficial insectsCalendula Pretty, too1Leafy Greens Tasty, too!Squash Lots of OM!50Introducing Organic Matter to Soil

Introducing Organic Matter to SoilFixing NitrogenLegumes can extract nitrogen from the atmosphere to make it available to plantsNitrogen is one of the most important plant nutrients but is difficult to maintain in soilsLeguminous cover crops include:Beans and peasWinter Peas or Field PeasFava beansVetchCloverAlfalfaFixing NitrogenLegumes can extract nitrogen from the atmosphere to make it available to plantsNitrogen is one of the most important plant nutrients but is difficult to maintain in soilsLeguminous cover crops include:Beans and peasWinter Peas or Field PeasFava beansVetchCloverAlfalfa52Introducing Organic Matter to SoilFixing NitrogenLegumes will not fix nitrogen if:Soil is high in N alreadySoil is saturated with water or overly drySome soils may need to be inoculated with proper organisms to form root associationsRoots develop small nodes which are red when actively fixing nitrogen

Fixing NitrogenLegumes will not fix nitrogen if:Soil is high in N alreadySoil is saturated with water or overly drySome soils may need to be inoculated with proper organisms to form root associationsRoots develop small nodes which are red when actively fixing nitrogen53Introducing Organic Matter to Soil

Introducing Organic Matter to SoilProtect soil from impact of rainWinter rains can damage soil structure and promote soil erosionCover crops protect the soilMust be planted early enough to get establishedCan be tough to balance with cash crops!Winter-killed crops may mulch the soile.g., Oats

Protect soil from impact of rainWinter rains can damage soil structure and promote soil erosionCover crops protect the soilMust be planted early enough to get establishedCan be tough to balance with cash crops!Winter-killed crops may mulch the soilE.g., Oats55Introducing Organic Matter to SoilSuppress WeedsMany cover crops are allelopathic they suppress the growth of other cropsFall ryeSunflowersMustardsBuckwheatGrows fast to outcompete weeds

Suppress WeedsMany cover crops are allelopathic they suppress the growth of other cropsFall ryeSunflowersMustardsBuckwheatGrows fast to outcompete weeds56Introducing Organic Matter to SoilSuppress Insect PestsSome crops suppress insect pestsMustardsBuckwheatWirewormsSuppress Insect PestsSome crops suppress insect pestsMustardsBuckwheatWireworms57Introducing Organic Matter to SoilProvide pollen for beesBuckwheat PhaceliaProvide pollen for beesBuckwheat Phacelia58Introducing Organic Matter to Soil

Introducing Organic Matter to SoilCover Crop Management PointsCan be planted in spring, summer or fallMost plantings in fall or late summer for overwinteringEarlier planting gets crop better established for winter soil coverCrop has more time to absorb soil nitrogenDo not over seed! Crop will compete with itselfCrops can be mixed to gain more benefitOM and N-fixing

Cover Crop Management PointsCan be planted in spring, summer or fallMost plantings in fall or late summer for overwinteringEarlier planting gets crop better established for winter soil coverCrop has more time to absorb soil nitrogenDo not over seed! Crop will compete with itselfCrops can be mixed to gain more benefitOM and N-fixing60Introducing Organic Matter to SoilCover Crop Management PointsCut crop and incorporate crop into soil before it flowers (unless you want flowers to attract bees)Incorporate in time to allow for decomposition before next crop is plantedIf smothering cover crops allow for a much longer period of decomposition

Cover Crop Management PointsCut crop and incorporate crop into soil before it flowers (unless you want flowers to attract bees)Incorporate in time to allow for decomposition before next crop is plantedIf smothering cover crops allow for a much longer period of decomposition61Introducing Organic Matter to SoilCover Crop Management PointsCrop rotation planning needs to consider cover cropsCover crop needs are different in small and large scale systemsMore important in large scale systemsCan take a way precious growing time in smaller systemsCover crops are a vital piece of a sustainable, closed-loop agroecosystemCover Crop Management PointsCrop rotation planning needs to consider cover cropsCover crop needs are different in small and large scale systemsMore important in large scale systemsCan take a way precious growing time in smaller systemsCover crops are a vital piece of a sustainable, closed-loop agroecosystem

62

63