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Soil Organic Matter=SOM AGROTEK 2009

Is this a healthy soil? Is this a healthy field?

SOM

Soil Organic matter encompasses all organic components of a soil:

Fresh residuesDecomposing organic matterorganic matterStable organic matterLiving organisms

Soil Organic MatterSoil organic matter -

all living organisms (microorganisms, earthworms, etc), fresh residues (old plant roots, crop residues, recently added manures), well-decomposed residues (humus) (humus).

The SOM content of agricultural topsoil is usually in the range of 1 to 6%. This amount is the result of all additions and losses of SOM that have occurred over the years. Citizen Science – Kansas State

Fresh Residues

Up to 15% of organic matter is fresh residue Comprised mainly of litter fallMuch can be recognized as plant residue

Decomposing Organic Matter

Plant material is transformed from one organic compound to another mainly by organisms in the soil so Organisms create by-products, wastes, and cell tissueCompounds released as waste by one organisms can often be used as food by another

Soil Organic Matter =SOMSOM is labile* -it can decline rapidly if the soil environment changes and renewablechanges and renewable -it can be replenished by inputs of organic material to the soil.

* Labile = Constantly or readily undergoing chemical, physical, or biological change or breakdown; unstable.

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Adequate levels of SOM can be maintained with:

proper fertilization, crop rotations, and tillage practices Returning crop residues to the soil.

Decomposition of Plant Residues(Under aerobic conditions)

PlantResidues

CO2

+More microbial biomass

NH4+, SO4

2-, etc. (inorganic waste)

Humus (organic waste)

+DeadMicroorganisms

Decomposition of Organic Matter

Organic materials are decomposed by heterotrophic microorganisms. The organic matter is a source of _______, carbon__________, and _____________ to these organisms.

energy nutrients

Composition– Jaringan hijau terdiri dari Air 75 %– Bahan kering Tanaman dewasa

Gula dan pati 1-5%Karbohidrat Hemiselulosa 10-28%

Sellulosa 20-50%

Lemak,lilin,tanin 1-8%Lignin 10-30%

Protein Sederhana larut air 1-15%dan protein kompleks

Form Formula Decomposition Composition____________________________________________________________________________________

Cellulose (C6H10O5)n rapid * 15-50%

Hemicellulose 5-35%

glucose C6H12O6 moderate-slow

galactose

mannose

xylose C5H10O5 moderate-slow

Lignin(phenyl-propane) slow 15-35%

Crude Protein RCHNH2COOH** rapid 1-10%

Polysaccharides

Chitin (C6H9O4.NHCOCH3)n rapid

Starch glucose chain rapid

Pectins galacturonic acid rapid

Inulin fructose units

____________________________________________________________________________________

* - decomposition more rapid in the presence of N

** - amino acid glycine (one of many building blocks for proteins)

PERUBAHAN SENYAWA ORGANIK DALAM TANAH

I. SENYAWA DALAM JARINGAN TANAMAN SEGARSukar didekomposisi Mudah didekmposisi

Lignin CellulosegFats/lemak Starches/patiOils/minyak Sugars/gulaResin Proteins

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II. SENYAWA INTERMEDIER DLM DEKOMPOSISISenyawa resisten mudah didekomposisi

Resins Amino acidsWaxes/lilin AmidesOils and Fats AlcoholsOils and Fats AlcoholsLignin Aldehydes

III.Hasil Proses Dekomposisi dlm tanahSenyawa kompleks Hasil akhir sederhanaHumus- a colloidal complex carbon dioxide and waterHumus a colloidal complex carbon dioxide and water

nitratessulfatesphosphatescalcium compounds

Laju Dekomposisi(Proses Pembakaran - Oksidasi)

1. Sugars - Starches - simple proteins Cepat2. Crude proteins3 H i ll l3. Hemicellulose4. Cellulose5. Lignins, fats, waxes Sangat lambat

40

60

80

100

Totalorganicmatter

al c

ompo

nent

left,

gra

ms

0

20

0 1 2 3 4 5

Cellulose

Lignin

Hemicellulose

Orig

ina

Years

Figure 1.2. Decomposition leaf litter.

Chemical Composition of Plant Residues

Sugars Complex proteins Hemicellulose Cellulose LigninSimple proteins WaxesStarchs

Increasing chemical complexity

Increasing rate of decomposition

1. As decomposition proceeds, water soluble fractions (sugars, starch,organic acids, pectins and tannins and array of nitrogen compounds)readily utilized by microflora.

2. Ether and alcohol-soluble fractions (fats, waxes, resins, oils),hemicelluloses and cellulose decrease with time as they are utilized ascarbon and energy sources.

3. Lignin, persists and can accumulate in the decaying biomass because ofits resistance to microbial decomposition.

4. Decomposition rates of crop residues are often proportional to theirlignin content and some researchers have suggested that the ligninlignin content and some researchers have suggested that the lignincontent may be a more reliable parameter for predicting residuedecomposition rates than the C:N ratio.

5. Vigil and Kissel (1991) included the lignin-to-N ratio and total soil Nconcentration (in g/kg) as independent variables to predict potential Nmineralization in soil. They also noted that the break point between netN mineralization and net immobilization was calculated to be at a C/Nratio of 40.

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The Carbon CycleCO2

Animal

Farm ManureGreen Manure& Crop Residue

To Atm.

- cycle of life energy cycle

Soil Reactions& Crop Residue

Microbial ActivityCarbonDioxide

CO3 , HCO3

Drainage losses CO2 & Carbonates & Bicarbonates of Ca, Mg, K, Etc.

C:N Ratio

Why is the C:N ratio important?Microorganisms need C and N in fixed ratios, because C and N are used to synthesize proteins, nucleic acids, etc.Bacterial cell C:N is 5:1 to 8:1. Since about 50% of the C in an organic material is converted to CO2, they need roughly a C:N of 10:1 to 16:1 in the residue they consume.Fungi need a C:N of about 40:1 in their diet

decomposition

C:N Ratio

50 g C20 g as CO2

20 g as biomass10 g as waste

Microbial biomass has an averageC:N of 10:1, therefore how much Nis needed to balance the new biomassC?

2 g

Therefore, if the residuecontaining 50 g of Ccontains < 2 g of N (C:N>25:1), it will haveinsufficient N for microbial needs. What about >2 g N (C:N <25:1)

Carbon : Nitrogen Ratio

Carbon : Nitrogen ratio relatif stabil dlm tanahC/N pada tnh yg diusahakan 10 or 12:1 (umumnya)TANAMAN Legumes 20:1

Straw 90:1Sawdust 150:1

Jadibahan organikmengandung C tinggi namun N rendah

Carbon : Nitrogen Ratio

Increase

New NO3 Levelof soil

Activity of DecayOrganisms &Evultion of

CO2Levelf il

Residues withwide C/N ratioadded to soil here

NO3 Depression Period

Time

of soil

C:N Ratio and Residue Mgmt.

What are the implications of the C:N ratio of crop residues for nutrient management?

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Immobilization

The conversion of inorganic (available) N (NHThe conversion of inorganic (available) N (NH44++, NO, NO33

--) ) to microbial biomass N. Results from...to microbial biomass N. Results from...

C:N ratio of residues

NH

NH

44++an

d N

Oan

d N

O33-- ))

TimeTime

CO2

release

Mineralization

The conversion of organic (unavailable) N to NHThe conversion of organic (unavailable) N to NH44++ . .

Results from...Results from...

C:N ratio of residues

NH

NH

44++

TimeTime

CO2

release

C:N ratio of residues

60

40

20

0

Net Mineralization

C:N

80

Net Immobilization

4 to 8 Weeks

Time

CO Evolution2NO 3

-

CO2

3-New NO Leve

Amount

Cultivation and addition of straw, N immobilization & mineralization of N, evolution of CO2

How is SOM Measured?

SOM is usually measured in the laboratory as organic carbon,

Soil organic matter is estimated to contain 58% organic carbon (varies from 40 to 58%) with the rest of the SOM comprising of other elements (eg 5% N 0 5% P and 0 5% S) (eg, 5% N, 0.5% P and 0.5% S).

A conversion to SOM from a given organic carbon analysis requires that the organic carbon content be multiplied by a factor of 1.72 (1.00/0.58).

Thus, 2% SOM is about 1.2% organic carbon.

Testing for Soil Organic CarbonUF/IFAS Extension Soil Testing Laboratory

Active Fraction

10 to 30% of the soil organic matter (active fraction) is responsible for maintaining soil microorganisms microorganisms. The active fraction of organic matter is most susceptible to soil management practices. (Inactive = humus)

ACTIVE

Adding Fresh OMIn a soil which at first has no readily decomposable materials, adding fresh tissue under favorable conditions: 1) immediately starts rapid

ADDED

starts rapid multiplication of bacteria, fungi, and actinomycetes, 2) which are soon actively decomposing the fresh tissue.

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Fresh SOMas most readily available energy sources are used up, microorganisms again become relatively inactive, leaving behind a dark mixture usually

f d t hreferred to as humus– a stable organic compound

Stable Organic Matter -Humus

Thus, soil organic compounds become stabilized and resistant to further changes by microorganismsStabilized organic matter Stabilized organic matter acts like a sponge and can absorb six times its weight in water

Humus

The stable portion of soil organic matter that results from microbial degradation of residues.

Dark coloredAbout 58% C, 5% NComplex chemical structure, aromatic plus aliphatic functional groupsDifficult to break down because of structurehigh CEC

Humus

The major organic “waste” by-product of OM degradation.The percentage of a residue that will become humus is approx proportional to its ligninhumus is approx. proportional to its lignin content.

Humus

CarbonHydrogenHydrogenOxygenNitrogen

HUMUSNewly-formed humus=a) combination of resistant materials from the original plant tissue, b) compounds synthesized as part of the microorganisms' tissue which remain as the organisms die. (Fluvic and

Leaf Humus

organisms die. (Fluvic and Humic Acid)humus is resistant to further microbial attack-N and P are protected from ready solubility.

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Function of Humusholds water and nutrients; it sticks together & helps establish and maintain a strong crumb structure & thus reduce soil erosionit provides some nutrients (N & P) as it is slowly decayed by microbial activity, Buffers effects of Buffers effects of pesticides humus decomposes at the rate of 2.5% per yearCreates good soil “ Tilth”Coates the sand, silt, clay particles making them dark and the darker the color, the greater the amount of soil humus present.

Humus = High Medium Low

Roles of Soil Organic Matter

Microbial substrateNutrient reserve (esp. N, P, S)CEC W t H ldi itWater-Holding capacitySoil structure

SOM Maintains soil “Tilth”

aiding infiltration of air and water promoting p gwater retention reducing erosion

BMI

Pengaruh Bahan Organik thd Sifat Tanah1. Warna tanah – coklat sampai hitam2. Mempengaruhi sifat kimia

- mendorong granulasig g- mengurangi plastisitas dan kohesi- kemampuan mengikat air meningkat

3. Kemampuan mengikat air meningkat- 2 x 20 x clay- 30 - 90% kemampuan mengikat air tanah mineral

4. Supply and availability of nutrientspp y y- N, P and S held in organic forms- Manure (10 - 5 - 10)/ ton (5 - 1 - 5)

N P K Available

5 Meningkatkan KPK

6 Stabilisasi unsur hara/tdkmudah terlindi

7 Tanah gembur dan dalam

8 Mengurangierosi

9 M k d t d BD9 Mengurang kepadatan dan BD

10. Menyediakan makanan utkmokroorganisme

11. Meningkatkan aktif Cacing tanah

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Management Effects on SOM

Agricultural management of soils usually _____________ amounts of SOM (compared to undisturbed soils) because:

decreases

tillage increases aeration and aerobic microbial activityliming, where practiced, increases microbial activityirrigation may increase microbial activityerosion

Adequate levels of SOM can be maintained with:

proper fertilization, crop rotations, and tillage practices Returning crop residues to the soil.

Conserving SOM

Management practices that can help conserve or build SOM:

Reduced (minimum) tillageCover cropsCover crops Growing high residue cropsAdding organic materials to soilsPracticing crop rotation

Effects of Cropping on SOM - Oklahoma

1.5

2

2.5oi

l % C

0

0.5

1

1880 1900 1920 1940 1960 1980 2000

So

Unfertilized Wheat Wheat + manure

Effects of Cropping on SOM - Oklahoma

1.5

2

2.5

oil %

C

0

0.5

1

1880 1900 1920 1940 1960 1980 2000

So

Unfertilized Wheat Wheat + manure

SOM = SOIL HEALTH

Measuring SOM is one step in assessing overall soil quality or soil health -measuring various key attributes of soil organic

d l

“If your soil clods can't pass the water test, change your management practices. It will help your bottom line as well as the soil.” – Ray Weil – Univ of Maryland

gmatter quantity and quality will give an indication of the health of the soil. Or Look at the state of the soil organisms in the soil.Or look at how well the soil “Holds Together”.

Simple clod test: Healthy soil, at left, holds together in water, while poor soil falls apart.

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Use of Soil Quality

1) Match use and management of land to soil capability, because improper use of a soil can damage it and the ecosystem.2) Establish a baseline understanding about soil quality so that we can NatureWatchq yrecognize changes as they develop. 3) Use baselines to determine if soil quality is deteriorating, stable, or improving.Thus soil quality becomes a good indicator of the health of an ecosystem.

Soil Quality

Soil quality is the capacity of soils within landscapes to sustain biological productivity, maintain environmental quality, and promote plant and animal http://www.directs

eed.org/soil qualit

health.

Protecting soil quality like protecting air quality and water quality should be fundamental goal of our Nation’s Environmental Policy

g _qy.htm

http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14

Poor Good

SOIL HEALTH

Soil Health is the change in Soil Quality over time due to human use and management or to natural events.Descriptive terms for Soil Health

Organic Matter - high

Cornell researcher George Abawi describes soil health strategies at an Onion Council field day in Wayne County, N.Y.Photo by Carol R. MacNeil.

In Vernon and surrounding counties are the largest concentration of organic farmers in Wisconsin.

Organic Matter - highCrop appearance = green, healthy,lusherosion – Soil will not erodeearthworms – numerousinfiltration – fast, no pondingCompaction - minimal

What is the health of this soil?