Soil Organic Matter Fresh Residues - Soilers | Soil is Life · Soil organic matter is estimated to...
Transcript of Soil Organic Matter Fresh Residues - Soilers | Soil is Life · Soil organic matter is estimated to...
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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
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“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?