Which soil would you Which soil would you pick to grow plants in pick to grow plants in your garden?your garden?

THE VALUE OF SOIL ORGANIC MATTER THE VALUE OF SOIL ORGANIC MATTER

A.A. B.B.

What is Soil Organic Matter?What is Soil Organic Matter?

•• Definition:Definition:

““The organic fraction of soil including plant, The organic fraction of soil including plant, animal, and microbial residues, fresh and at animal, and microbial residues, fresh and at all stages of decompositionall stages of decomposition…… and highly and highly carbonized compounds such as charcoal, carbonized compounds such as charcoal, graphite and coalgraphite and coal””

Soil organic matterSoil organic matter == (2 x C) + O, H, N, P, S, (2 x C) + O, H, N, P, S, etc.etc.

FUNCTIONS OF SOIL ORGANIC MATTERFUNCTIONS OF SOIL ORGANIC MATTER

SOIL ORGANIC MATTER AND SUSTAINABILITYSOIL ORGANIC MATTER AND SUSTAINABILITY

•• Provides soil nutrients and enhances soil Provides soil nutrients and enhances soil nutrient availability over several growing nutrient availability over several growing seasons.seasons.

•• Improves soil physical, chemical and Improves soil physical, chemical and biological properties for plant growth.biological properties for plant growth.

•• Buffers changes in soil properties due to Buffers changes in soil properties due to disturbance or variation in other disturbance or variation in other environmental factors (e.g. climate).environmental factors (e.g. climate).

•• Reduces environmental contamination and Reduces environmental contamination and soil loss.soil loss.

•• Possibly reduces need for external inputs and Possibly reduces need for external inputs and enhances internal recycling when crop enhances internal recycling when crop residues and/or organic soil amendments are residues and/or organic soil amendments are applied.applied.

RESERVOIR OF PLANT NUTRIENTSRESERVOIR OF PLANT NUTRIENTS

•• 95% or more of total N in soil is 95% or more of total N in soil is organic N organic N

•• If soil contains 0.2 % total N then:If soil contains 0.2 % total N then:

0.2 kg N/100 kg soil * 95% * 2,000,000 0.2 kg N/100 kg soil * 95% * 2,000,000 kg soil/hectare plow layerkg soil/hectare plow layer

= 3800 kg organic N/hectare plow= 3800 kg organic N/hectare plowlayer or layer or 3393 lb organic N/acre 3393 lb organic N/acre plow layerplow layer

CARBON IN SOILCARBON IN SOIL

•• What are the major forms of C in soil?What are the major forms of C in soil?

Organic residuesOrganic residues

SoilSoil

COCO22 (60(60--80%)80%)

Soil organisms Soil organisms (3(3--8%)8%)

NonhumicNonhumicsubstances (3substances (3--8%)8%)

ComplexComplex humichumicsubstances (10substances (10--30%)30%)

Organic residues in soilOrganic residues in soil

Soil humus (15Soil humus (15--35%)35%)

FORMS OF SOIL ORGANIC MATTERFORMS OF SOIL ORGANIC MATTER

Particulate organic matter and sand particles under magnificatioParticulate organic matter and sand particles under magnificationn

AGE OF SOIL ORGANIC CARBONAGE OF SOIL ORGANIC CARBON

Sample Description Mean Residence TimSample Description Mean Residence Timee------ yearsyears ------

Grassland soil (North Dakota)Grassland soil (North Dakota)Virgin soilVirgin soil 1,1751,175 ±± 100100ManuredManured orchardorchard 880880 ±± 7474

Bridgeport loam, WyomingBridgeport loam, WyomingSurface sod layerSurface sod layer 3,2803,280Clay fraction from virgin soilClay fraction from virgin soil 6,6906,690Continuous wheat plotContinuous wheat plot 1,8151,815

MollisolMollisol,, SaskatchewaSaskatchewaSurface soilSurface soil 545 to present545 to presentB horizonsB horizons 700 to 4,000700 to 4,000Buried horizonsBuried horizons 5,900 and 8,4105,900 and 8,410

MANAGEMENT PRACTICES THAT MANAGEMENT PRACTICES THAT DECREASE SOIL ORGANIC CARBONDECREASE SOIL ORGANIC CARBON

•• Frequent tillageFrequent tillage•• Burning for clearingBurning for clearing•• Removal of cropRemoval of crop

residuesresidues•• InadequateInadequate

fertilizationfertilization

•• Soil erosionSoil erosion

EFFECTS OF TILLAGE ON SOIL OMEFFECTS OF TILLAGE ON SOIL OM

LOSS OF SOIL ORGANIC C WITH TILLAGE LOSS OF SOIL ORGANIC C WITH TILLAGE

Sanborn Field

EFFECTS OF LANDEFFECTS OF LAND--USE ON SOIL OM IN USE ON SOIL OM IN THE TROPICSTHE TROPICS

Research conducted on theResearch conducted on thePacific island of GuamPacific island of Guam

LOSS OF SOIL ORGANIC MATTERLOSS OF SOIL ORGANIC MATTER

““Soil organic matter is one of our most important Soil organic matter is one of our most important national resources; its unwise exploitation has been national resources; its unwise exploitation has been devastating; and it must be given its proper rank in devastating; and it must be given its proper rank in any conservation policy as one of the major factors any conservation policy as one of the major factors affecting the levels of crop production in the futureaffecting the levels of crop production in the future””

William A. AlbWilliam A. AlbrechtrechtUniversity of MissourUniversity of Missouri (1938) i (1938)

LONGLONG--TERM SUSTAINABLE MANAGEMENT AND TERM SUSTAINABLE MANAGEMENT AND SOIL CARBONSOIL CARBON

Lowland Taro System in PalauLowland Taro System in Palau

PRACTICES THAT INCREASE SOIL PRACTICES THAT INCREASE SOIL ORGANIC MATTERORGANIC MATTER

•• Adopt conservation tillage, residue Adopt conservation tillage, residue management and mulch farmingmanagement and mulch farming

•• Apply organic wastes to soilApply organic wastes to soil•• Use N and other nutrient sources more Use N and other nutrient sources more

efficientlyefficiently•• Convert marginal and degraded lands to Convert marginal and degraded lands to

restorative land uses restorative land uses •• Adopt soil conservation practicesAdopt soil conservation practices•• Eliminate summer (bare) fallow and Eliminate summer (bare) fallow and

incorporate legumes and other appropriate incorporate legumes and other appropriate cover crops in rotationscover crops in rotations

Kimble et al., 2002Kimble et al., 2002

CONSERVATION TILLAGECONSERVATION TILLAGE

TillageTillage NoNo--TillTill

EFFECT OF ROTATIONS ON SOIL OMEFFECT OF ROTATIONS ON SOIL OM

SOIL C DISTRIBUTION WITH DIFFERENT SOIL C DISTRIBUTION WITH DIFFERENT LAND MANAGEMENT PRACTICESLAND MANAGEMENT PRACTICES

LSDLSD(0.10)(0.10) -------------------------- 2.42.4 ------------------------ ---------------------- 2.682.68 ------------------------ ------------------------ 22.222.2 ------------------------

LandscapeLandscape TOCTOC POM CPOM C DOCDOCposition GR AF CRposition GR AF CR GR AF CRGR AF CR GR AF CRGR AF CR

------------------------------------------------------ g kgg kg--11 soilsoil ---------------------------------------------------- ---------------- mg kgmg kg--11 soilsoil ------------

UpperUpper 19.519.5 24.524.5 19.519.5 3.543.54 6.606.60 3.033.03 106.8106.8 123.3123.3 80.180.1

MiddleMiddle 22.522.5 23.523.5 22.022.0 5.425.42 5.765.76 4.524.52 105.7105.7 147.2147.2 75.075.0

LowerLower 25.525.5 24.024.0 18.518.5 7.127.12 7.387.38 3.283.28 133.5133.5 124.6124.6 72.472.4

GreenleyGreenley AgroforestryAgroforestry Watershed ResearchWatershed Researchin Northeastern Missouriin Northeastern Missouri

RESIDUE QUALITY AND DECOMPOSITIONRESIDUE QUALITY AND DECOMPOSITION

•• Carbon to nitrogen of theCarbon to nitrogen of theresidue > 25 may result in residue > 25 may result in N deficiency in soil forN deficiency in soil forplant growth and slow downplant growth and slow downthe rate of decomposition.the rate of decomposition.

•• Plant residues containingPlant residues containinghigh proportions of ligninhigh proportions of ligninand tannins decompose relatively slower than otherand tannins decompose relatively slower than otherplant residues. Woody materials contain high plant residues. Woody materials contain high proportions of lignin. Oak leaves contain relatively highproportions of lignin. Oak leaves contain relatively hightannin content.tannin content.

•• The smaller the pieces of residue, the faster it will The smaller the pieces of residue, the faster it will decompose.decompose.

COMPACTION AND DECOMPOSITIONCOMPACTION AND DECOMPOSITION

May 11May 1100

1515

3030

4545

6060

July 20July 20

CompactedCompacted

NonNon--compactedcompacted

Sampling dateSampling date

CO

CO

22ef

flu

x (

effl

ux

( µµm

ol m

mo

l m--22

sec

sec--

11 ))

CompactionCompactionalso decreasedalso decreasedsoil moisturesoil moistureand increasedand increasedsoilsoiltemperaturetemperature

CompactedCompacted

NonNon--compactedcompacted

CheckHigh litter

EFFECTS OF GM CROPSEFFECTS OF GM CROPS

Rhizosphere

Crop residues

Managementpractices

Nutrient export

Pesticides

Root exudates

Tillage

Transgenic Crop

Fertilization

Gene transfer

Climate

Microbially-mediatednutrient transformations:

• Mineralization/immobilization• Oxidation/reduction• Fixation/gaseous loss• Solubilization

Soil properties:

• Clay type and content• pH• Soil structure• Soil organic matter

(Animal waste)

DIFFICULTY IN CREATING A CARBON DIFFICULTY IN CREATING A CARBON BALANCE???BALANCE???

Biosphere 2, designed to be an artificial, selfBiosphere 2, designed to be an artificial, self--contained, selfcontained, self--supporting ecosystem. All water, air supporting ecosystem. All water, air and nutrients were recycled in the structure. Had and nutrients were recycled in the structure. Had problems with maintaining atmosphere fit for life problems with maintaining atmosphere fit for life partially due to role of soil organic matter. partially due to role of soil organic matter.

http://www.bio2.eduhttp://www.bio2.edu

InIn GtGt oror GtGt/year/year11 GtGt =1 Pg=1 Pg= 10= 101515gg

GLOBAL CARBON CYCLE AND C SEQUESTRATIONGLOBAL CARBON CYCLE AND C SEQUESTRATION

Historic net loss of 66 Historic net loss of 66 –– 9090 GtGt C from soilC from soil

REASONSREASONSFOR CONSERVINGFOR CONSERVINGSOIL ORGANIC CSOIL ORGANIC C

ANYANYQUESTIONS?QUESTIONS?