Defining Agriculture

Aliphatic fatty acids and alkanes 10 - 20% 20% 10 - 20% N materials - amino acids, Carbohydrates amino sugars

40 - 60% Aromatic

SOIL ORGANIC CARBON COMPOSITION

Soil organic matter composition is remarkably similar from soil to soil over a broad range of climatic, topographic, and vegetative variations. Soil Quality

Important Soil Characteristics

Structure Texture Bulk density

Soil organic matter Water holding capacity Water infiltration rate pH Electrical conductivity Nutrient availability and release

Microbial biomass carbon and nitrogen Balanced biotic diversity ClassicalFractionation of Soil Organic Matter by Alkali, Acid,and Alcohol

SOIL ORGANICMATTER

TREAT WITH ALKALI

SOLUBLE INSOLUBLE (HUMIN) TREAT WITH ACID (pH1-2)( pH 1 - 2 )

SOLUBLE INSOLUBLE (FULVIC ACID) ( HUMIC ACID ) ( - HUMUS ) NaOH (pH 4.8 ) EXTRACT WITH ALCOHOL

SOLUBLE INSOLUBLE SOLUBLE INSOLUBLE (B - HUMUS) ( HYMATOMELOANIC ACID ) (HUMIC ACID ) FULVIC ACID

Mosthighly oxidized O.M.

Lowest molecular weight O.M.

Seriesof aromatic rings with large number of side chains

Usuallypolysaccharides and low molecular weight fatty acids are associated with F.A.

Flexible,open structure with void spaces

HighO 2 , low H 2 in comparison to H.A. (from Schnitzer)

Partial chemical structure for FA HUMIC ACID

Highermolecular weight O.M.

Hasability to form hydrogen bonds... thusprecipitating at low pH

Few carbohydrate residues

Highly condensed and aromatic

HighC, low O 2 in comparison to F.A.

aldehyde group

phenol group

methoxyl group hydroxyl group

ether linkage

carbonyl group

phenylphenyl group group

Lignin Structure FACTORSRESPONSIBLE FOR THE CHEMICAL STABILITY OFORGANIC COMPOUNDS IN SOIL

ENVIRONMENTAL FACTORS

1. Waterlogging 4. High salt content

2. Desiccation 5. Unfavorable pH

3. Low temperatures 6. Absence of microbial growth factorsand of decomposers 4. Presence of toxic factors

CHEMICAL FACTORS

1. Large molecular size of humic material

2. Disorderly condensation

3. Copolymerization with extensive cross-linkages

4. Smooth globular shape of humic material

5. Readily inactivates enzymes

6. The fact it is nondiffusable Radiocarbon Age of Organic Fractions of Two Canadian Soils.

Radiocarbon Age (yr)

Organic Fractions Melfort Soil Waitville Soil

Unfractionated soil 870+50 250+60

Fulvic acid +acid extract 470+60 50

Humic acids I ("mobile") 785+50 85+45

Humin 1135+50 335+50

Humic acids II ("total") 1235+60 195+50

Nonhydrolyzable 1400+60 ~1230

Hydrolyzable 25+50 ~465

Source: Adapted from Campbell et al. (1967) Radiocarbon Ageof some Canadian Soils and Organic Matter Fractions

% Organic Year Radiocarbon Organic SoilVegetation Matter Sampled Age (yr) Fraction

Greywooded Originalboreal forest, 3.4 1970 250 now cultivated Black chernozemic Melfort Originalgrassland, 00-15cm- 15 cm now cultivated 9.6 1970 870 1515-25cm- 25 cm ------960 Oxbow 7.8 1970 940 00-8cm- 8 cm 6.0 1974 20 1818-32cm- 32 cm 0.7 ------1340

Dark brown Virgingrassland 5.0 1970 420 chernozemic Cropped 2.0 1970 1960 Cropped + legume 2.5 1970 1500 Brown chernozemic Sceptre Virgin grassland 4.1 1970 525 <20Light fraction 2.6 1974 540 <20 HCl Hydrolysate 2.6 1970 350 Cropped 1765 HCl Residue 2.1 1974 430 1910 Humic acid 1330 Humin

Source: Adapted from Campbell et al. (1967). ENZYMATIC OXIDATIVECOUPLING REACTIONS

Oxidativecoupling is defined as a process by which phenolic oraromatic amines are linked together after oxidation by an enzymeor a suitable chemical reagent. Coupling produces C-CC - C , ,C-OC - O , ,C-NC - N , ,orN-Nor N - N bonds.

Importantin the synthesis of humic substances and other biological materials ( Lignins, tannins, alkaloids,antibiotics )

Responsiblefor the incorporation of many agricultural and industrial chemicals into soil organic matter.

Information is lacking on this subject because of the difficulty of obtaining enzymes of sufficient purity and the complexity of the products of oxidative coupling. +

Formation of aryloxy radicals from phenols

-E, -H

Enzyme

DESCRIPTION OF ENZYMES INVOLVED

Metal containing enzymes classified as either Monophenol Monooxygenases (EC 1.14.18.1) or Perioxidases (EC 1.11.1.7)

Monophenol Monoxygenases (Laccases, Tyrosinases)

Both enzymes contain copper, require molecular oxygen for activity, and do not require coenzymes.

Laccases Produce free radical intermediates Are glycoproteins Have a relatively limited substrate range

Tyrosinases Catalyze two types of reactions Cresolase activity Catecholase activity Do not produce free radical intermediates

Perioxidases

Contain iron, require H2 O2 for activity, often yield the same coupling products as laccases from phenolic substrates, and produce free radical intermediates. OH OH OH Cresolase

CH3 CH3

OH O OH O Catecholase Characteristics that Differentiate Laccase, Tyrosinase, and Peroxidase

Characteristic Laccase Tryosinase Peroxidase

Presence of Cu + + - Presence of Fe - - + Inhibition by CO - + - Occurrence of hydroxylation reaction - + - (+) Absorption spectra peaks at 280 nm + + a at 615 nm + - a

H2 O2 requirement - - +

a For spectra of peroxidases see Saunders et al. (1964) TWOTHEORIES OF HUMUS FORMATION

MODIFIEDLIGNIN THEORY

Humus is basically lignin material which has been slightly modifiedto form lignin - protein complexes resistant to microbialattack. ( Waksman)

microbes lignin - protein complex

POLYPHENOL THEORY

Decompositionof all plant components including lignin tosimple monomers occurs. Polymerization of active monomers into high molecular weight dark colored complexesfollows.

microbes

polymerization SEQUENCEOF REACTIONS IN HUMUS FORMATION FROM CARBOHYDRATES

Freeingof carbohycrates, breakdown to monomers

Openingof ring form of sugar

Additionof an amino group to the carbonyl C of the sugar ++++++ + + + + Rearrangementof the molecule to form formaN-a N - substituted keto derivative N

Dehydrationand fragmentation to yield unsaturated intermediates -

Polymerizationof intermediates to form brown-coloredcomplexes SEQUENCEOF REACTIONS IN HUMUS FORMATION FROM LIGNIN

Ligninis freed from plant residues during decomposition

FreedLignin is broken down into primary structural units

Theprimary units are oxidized and demethylated and the polyphenols are again oxidized to quinones

Quinonespolymerize with N compounds to form dark colored complexes

N N s of microbial

ances from lignin and product

Principal steps in the formation of humic subst synthesis formed by the condensation of amino acids with polyphenols (upper and middle) and sugars, through Maillard reaction (lower). MICROBIAL METABOLISM OF PHENOLICS ( vol. 1, chapter 12, Soil Biochemistry )

OXYDASES

Transferelectrons to O 2 to form H 2O or H 2O 2 without intervention of electron transport chain.

"Monooxygenases" - one oxygen atom introduced to the ring

"Dioxygenase" - two oxygen atoms are introduced and the ring is broken

MONOOXYGENASEREACTION

R R +O+HX+ O + H X +HO+X+ H O + X 2 2 2 OH H X is a reduced cofactor 2

DIOXYGENASEREACTION

OH COOH +O+ O 2 OH COOH GENERAL SCHEMEFOR THE DEGRADATION OF CATECHOL BY META FISSION

2 1 OH " catechol " OH

1 Thering is opened by a meta cleavage alongthe purple line

2 Secondcleavage occurs along the green line

OH CHO rearrangement CHO O of electrons 2 COOH COOH Cl OH C= Cl OH Cl O

O 22HH O O

= 2 O= = CH CH CH CCOOH + HCOOH C CH=CH-CH CCOOH ) 3 2 2 H Cl ( formic acid ) Cl

O

= CH CH Cl + CH CCOOH 3 2 3 " pyruvate " METABOLISM OF RING FUSION PRODUCTS ( ortho cleavage )

COOH COOH COOH OCOO OCOO COOH C C O O

b - ketoadipate muconate muconolactone lactone

+H+ H2 O

O succinic acid COOH COOH acetyl CoA O b - ketoadipic ( HOOC CH C CH CH COOH ) acid 2 2 2

"b - oxidation" RING FUSION OF DIHYDROXYPHENOLS

OH (O2 ) 1 pyrocatochelase COOH ( ortho cleavage ) OH COOH R ( catechol 11,,2 - oxygenase ) R "catechol"

CHO OH 2 (O ) COOH 2 ( meta cleavage ) OH ( catechol 22,,3 - oxygenase ) R R OH

OH COOH COOH 3 (O2 ) COCOOH

OH OH

"gentisic acid" "maleylpyruvate"

OH COOH 4 COOH COCH COOH (O2 ) 2

OH OH

"homogentisic acid" "maleyl acetoacetate" DEGRADATION OF NAPHTHALENE

OH monooxygenase OH

+2O+ 2 O2 ring fission

"napththalene" O COOHOH 1 6 2

5 3 rearrangement 4 of electrons

OH OH 6 O COOH 6 O COOH 1 water 1 pyruvate 2 2

3 addition 3 5 5 4 4 OH

O CHCH C COOH 2 OH

OH OH OH

CHO COOH OH

"catechol" I

Cultivation starts

I Virgin grassland

I

I

I

Organic Matter (%C)

I 1.8 2.2 2.6 3.0 3.4 3.8 Time after cultivation I I I I I 0 50 100 150 200 250

Time (Years) Voroney et al. CHANGES IN SOIL ORGANIC CARBON

Decrease in organic C physically protected in soil.

Decreases in organic C range from 20-50% of initial amount.

Steady state is not reached even after long time periods.

Biological decomposition is the major factor for organic C loss. Erosion may also be important.

When soil erodes, much more organic matter is lost (percent-wise) than mineral soil.

Erosion

%

% Mineral soil Organic Matter δ13C Values for Soil Carbon under Plants with a C-3 Metabolism and for the Same Soil after the Growth of a C-4 Plant.

13 Depth (cm) % C δ C 0\00 C-3 Vegetation Plant - - -30.8 Topsoil 0-5 9.1 -27.3 Subsoil 55-60 1.1 -27.4

C-4 Vegetation Plant - - -12.5 Topsoil 0-10 4.8 -26.1 Subsoil 49-55 1.5 -25.3

Source: Adapted from Stout et al. (1975)

0.3 Glutamic Acid PN

PS 0.2

D/L

0.1 III

0 Soil E RI R AII AI

0.3 Alanine PN PS 0.2

D/L

0.1 III

0 Soil E RI R AII AI Fertility and Environmental Benefits (Hoytville Site) Fertility and Environmental Benefits (Wooster Site) Organic Carbon Concentrations (%) Soil Depth (cm) Soil OrganicOrganic CarbonCarbon (Mg/ha)(Mg/ha)

No-till

Continuous CornCorn Plow till

(cm)

Depth (cm) Corn -- SoybeanSoybean

Corn -- OatsOats - Meadow- Meadow

The SOCSOC profileprofile underunder conventionalconventional andand no-tillno-till systemssystems for differentdifferent cropcrop rotrotationsations inin NWNW Ohio.Ohio. -1

Soil Organic C (Mg ha )

51015202530 II IIII IIIII 0 40 80 120 160 200 Fertilizer N rate (kg ha-1 )

Soil Depth Tillage Black 0-5 cm NT Red 5 -15 cm CT Blue 15-30 cm Carbon Sequestration

Summary

The use of cover crops, adequate N fertilization, crop residues left in the field, and erosion control clearly can lead to sequestering of C in the soil, especially where it has been depleted due to intensive cultivation or previous erosion.

No-tillage is best able to incorporate almost all of the above actions into a single cropping system.

Time scales of 20 to 50 years seem to be required before major amounts of C sequestration and accumulation is achieved.

C sequestration brought about by NT practice is not very stable and will be rapidly mineralized if tillage is applied. Periodic tillage followed by NT may stabilize organic C levels in soil, but will probably not result in a net increase. BENEFITSOF NO-TILL

Highergrain yield

Protectssoil from erosion by wind and rain Improveswater quality Conserves water

equipmentAddsorganic wear matter to soil

Reduceslabor, fuel, and equipment wear

Provideshabitat for wildlife

Reducesrelease of carbon gases

Biologicallife is increased ( earthworms and microbial population )

(earthwormsand microbial population)