Defining Agriculture

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George Boone
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1 Defining Agriculture

3 10-0% Carbohydrates Aliphatic fatty acids and alkanes 10-0% 0% N materials - amino acids, 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.

4 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

5 Classical Fractionation of Soil Organic Matter by Alkali, Acid, and Alcohol SOIL ORGANIC MATTER TREAT WITH ALKALI SOLUBLE TREAT WITH ACID (ph1-) INSOLUBLE (HUMIN) SOLUBLE (FULVIC ACID) Na ( ph 4.8 ) INSOLUBLE ( HUMIC ACID ) ( - HUMUS ) EXTRACT WITH ALCOL SOLUBLE INSOLUBLE ( B - HUMUS) SOLUBLE INSOLUBLE ( HYMATOMELOANIC ACID ) ( HUMIC ACID )

6 FULVIC ACID Most highly oxidized O.M. Lowest molecular weight O.M. Series of aromatic rings with large number of side chains Usually polysaccharides and low molecular weight fatty acids are associated with F.A. Flexible, open structure with void spaces High O, low H in comparison to H.A.

7 Partial chemical structure for FA (from Schnitzer)

8 HUMIC ACID Higher molecular weight O.M. Has ability to form hydrogen bonds... thus precipitating at low ph Few carbohydrate residues Highly condensed and aromatic High C, low O in comparison to F.A.

10 aldehyde group phenol group hydroxyl group methoxyl group ether linkage carbonyl group phenyl group Lignin Structure

11 FACTORS RESPONSIBLE FOR THE CHEMICAL STABILITY OF ORGANIC COMPOUNDS IN SOIL ENVIRONMENTAL FACTORS 1. Waterlogging. Desiccation 3. Low temperatures 4. Presence of toxic factors 4. High salt content 5. Unfavorable ph 6. Absence of microbial growth factors and of decomposers CHEMICAL FACTORS 1. Large molecular size of humic material. 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

12 Radiocarbon Age of Organic Fractions of Two Canadian Soils. Radiocarbon Age (yr) Organic Fractions Melfort Soil Waitville Soil Unfractionated soil Fulvic acid +acid extract Humic acids I ("mobile") Humin Humic acids II ("total") Nonhydrolyzable ~130 Hydrolyzable 5+50 ~465 Source: Adapted from Campbell et al. (1967)

13 Radiocarbon Age of some Canadian Soils and Organic Matter Fractions % Organic Year Radiocarbon Organic Soil Vegetation Matter Sampled Age (yr) Fraction Grey wooded Black chernozemic Melfort 0-15cm 15-5cm 15-5 cm Oxbow Oxbow 0-8cm 18-3cm Original boreal forest, now cultivated Original grassland, now cultivated Dark brown chernozemic Brown chernozemic Sceptre Virgin grassland Cropped Cropped + legume Virgin grassland Cropped <0 Light fraction <0 HCl Hydrolysate 1765 HCl Residue 1910 Humic acid 1330 Humin Source: Adapted from Campbell et al. (1967).

14 ENZYMATIC OXIDATIVE COUPLING REACTIONS Oxidative coupling is defined as a process by which phenolic or aromatic amines are linked together after oxidation by an enzyme or a suitable chemical reagent. Coupling produces C-C C,C-O,C-N,or N-N N bonds. Important in the synthesis of humic substances and other biological materials ( Lignins, tannins, alkaloids, antibiotics ) Responsible for 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.

15 -E, -H + Enzyme Formation of aryloxy radicals from phenols

17 DESCRIPTION OF ENZYMES INVOLVED Metal containing enzymes classified as either Monophenol Monooxygenases (EC ) or Perioxidases (EC ) 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 Perioxidases Catecholase activity Do not produce free radical intermediates Contain iron, require H O for activity, often yield the same coupling products as laccases from phenolic substrates, and produce free radical intermediates.

18 Cresolase CH 3 CH 3 Catecholase O O

19 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 80 nm at 615 nm (+) a a H O requirement a For spectra of peroxidases see Saunders et al. (1964)

20 TWO THEORIES OF HUMUS FORMATION MODIFIED LIGNIN THEORY Humus is basically lignin material which has been slightly modified to form lignin - protein complexes resistant to microbial attack. ( Waksman) lignin - protein complex microbes POLYPHENOL THEORY Decomposition of all plant components including lignin to simple monomers occurs. Polymerization of active monomers into high molecular weight dark colored complexes follows. microbes polymerization

21 SEQUENCE OF REACTIONS IN HUMUS FORMATION FROM CARBYDRATES Freeing of carbohycrates, breakdown to monomers Opening of ring form of sugar Addition of an amino group to the carbonyl C of the sugar Rearrangement of the molecule to form a N - substituted keto derivative N Dehydration and fragmentation to yield unsaturated intermediates Polymerization of intermediates to form brown-colored complexes

22 SEQUENCE OF REACTIONS IN HUMUS FORMATION FROM LIGNIN Lignin is freed from plant residues during decomposition Freed Lignin is broken down into primary structural units The primary units are oxidized and demethylated and the polyphenols are again oxidized to quinones Quinones polymerize with N compounds to form dark colored complexes N N

23 Principal steps in the formation of humic substances from lignin and products of microbial synthesis formed by the condensation of amino acids with polyphenols (upper and middle) and sugars, through Maillard reaction (lower).

24 MICROBIAL METABOLISM OF PHENOLICS ( vol. 1, chapter 1, Soil Biochemistry ) OXYDASES Transfer electrons to O to form H O or H O 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 MONOOXYGENASE REACTION R + O + H X R H X is a reduced cofactor + H O + X DIOXYGENASE REACTION + O CO CO

25 GENERAL SCHEME FOR THE DEGRADATION OF CATECHOL BY META FISSION 1 " catechol " 1 The ring is opened by a meta cleavage along the purple line Second cleavage occurs along the green line rearrangement CHO CO of electrons O Cl Cl = O CH 3CH CH CCO + HCO ( formic acid ) O = Cl CH3 CH Cl + CH 3CCO " pyruvate " CHO CO C= Cl H O O = H O O = C CH=CH-CH CCO ) Cl

26 METABOLISM OF RING FUSION PRODUCTS ( ortho cleavage ) CO CO CO O C O CO O C O muconate muconolactone - ketoadipate lactone +H O acetyl CoA succinic acid O ( HOOC CH C CH CH CO ) O CO CO - ketoadipic acid " - oxidation"

27 RING FUSION OF DIHYDROXYPHENOLS 1 R "catechol" (O ) pyrocatochelase ( catechol 1, - oxygenase ) R CO CO ( ortho cleavage ) (O ) CHO CO ( meta cleavage ) R ( catechol, 3 - oxygenase ) R 3 CO (O ) CO COCO "gentisic acid" "maleylpyruvate" 4 CO (O ) CO COCH CO "homogentisic acid" "maleyl acetoacetate"

28 DEGRADATION OF NAPHTHALENE monooxygenase + O ring fission "napththalene" 6 O 1 CO rearrangement of electrons pyruvate 6 O CO 1 water 6 O CO addition O CH CH C CO CHO CO "catechol"

29 Organic Matter (%C) I I I I I I Cultivation starts Virgin grassland Time after cultivation I I I I I Time (Years) Voroney et al.

30 CHANGES IN SOIL ORGANIC CARBON Decrease in organic C physically protected in soil. Decreases in organic C range from 0-50% 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 % % Organic Matter Mineral soil

31 δ 13 C Values for Soil Carbon under Plants with a C-3 Metabolism and for the Same Soil after the Growth of a C-4 Plant. Depth (cm) % C δ 13 C 0 \00 C-3 Vegetation Plant Topsoil Subsoil C-4 Vegetation Plant Topsoil Subsoil Source: Adapted from Stout et al. (1975)

33 D/L I I I PN PS Glutamic Acid 0 Soil E R R A A I II I D/L I I I PN PS Alanine 0 Soil E R R A A I II I

34 Fertility and Environmental Benefits (Hoytville Site)

35 Fertility and Environmental Benefits (Wooster Site) Organic Carbon Concentrations (%) Soil Depth (cm)

36 Soil Organic Carbon (Mg/ha) No-till Continuous Corn Plow till Depth (cm) Corn - Soybean Corn - Oats - Meadow The SOC profile under conventional and no-till systems for different crop rotations in NW Ohio.

37 Soil Organic C (Mg ha ) I I I I I I I I I I I Fertilizer N rate (kg ha -1 ) Soil Depth Black 0-5 cm Red 5-15 cm Blue cm Tillage NT CT

38 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 0 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.

39 BENEFITS OF NO-TILL Higher grain yield Protects soil from erosion by wind and rain Improves water quality Conserves water equipment Adds organic wear matter to soil Reduces labor, fuel, and equipment wear Provides habitat for wildlife Reduces release of carbon gases Biological life is increased ( earthworms and microbial population ) (earthworms and microbial population)

Soil organic matter composition, decomposition, mineralization and immobilization

Soil organic matter composition, decomposition, mineralization and immobilization SOIL ORGANIC MATTER Substances containing carbon are organic matter. Soil organic matter consists of decomposing plant