Composting on Your Small Farm
Jason Faucera
Clackamas SWCD Conservationist
jfaucera@conservationdistrict.org
503-210-6013
Nick Andrews
OSU Small Farms Horticulturist
nick.andrews@oregonstate.edu
503-913-9410
Definition of Composting
Controlled and efficient
transformation of raw organic materials…
Definition of Composting
into
biologically stable, humus-rich substances
suitable for growing plants and
pose no hazard to health and environment
On-Farm
Composting
Crop &
Livestock
Waste
High Quality
Food and
Forage
Closed
Nutrient
Cycle
Soil
Amendment
Healthy Soil
Healthy
Crops
Compost topics
1.
2.
3.
4.
5.
Site selection
Composting methods
The composting process
Compost quality and testing
Compost application
Site Selection
• Operate seasonally or year-round
• Volume of materials and space for composting, curing, and
storing
• Access for feedstock delivery and heavy equipment
• Access to move finished compost to fields
• Supporting heavy equipment traffic during the rainy season
• Depth of the seasonal high water table
• Proximity to drinking water wells and septic systems
• Site Topography and its distance from surface water,
including ditches, wells, and tile drains
Soils and Underlying Strata
• Characterize your
soils: NRCS Web
Soil Survey
– Fine-textured soils
(clay) drain poorly
but also can help
protect aquifer
– Coarse-textured
soils: opposite
Compost Site Layout & Design:
Non-Permanent Structures
How Big a Site Do You Need?
• Determine Volume of Feedstock and when it
will be generated or delivered
• How will you move materials and turn your
piles? (aisles, edge areas)
• Calculate pile or windrow size:
– Windrow volume= L x W x H x 2/3 (rounded)
– Remember that piles shrink as they compost
• Combine piles when possible: reduce surface area
Marc Anderson
Smoky Hills Farm & O2 Compost
Method
Cost
PFRP
Duration
Turning frequency
Windrow –
loader
Minimal added
investment
May not be
6-12 mo
consistently met
3-4 times when active & 1-2
times when curing
Windrow –
turner
Specialty equipment
Routinely met
w/in 15 days
2-6 mo
4-5 times when active & 2-3
times when curing
Aerated
static pile
Engineering &
design consultation
Routinely met
w/in 3 days
2-4 mo
Feedstock blended when
building piles and moving to
curing piles
Covers
Chakola’s Place & O2 Compost
WSU Puyallup
Covers?
• Pile shape: tall narrow piles with steep sides shed
rain
• Low risk (WQ) feedstock less likely to generate
leachate
• Active piles evaporate moisture, curing piles
don’t
• What time of year are curing piles stored?
• Scale matters – large composting sites pose more
potential risk
• Clean pile edges: many small piles on a site
generate lots of leachate
Manage Run-off and Leachate
• What are Runoff and Leachate?
• BOD: Biological Oxygen Demand of organics
• When is compost
safe?
• Nitrate, pathogens
other nutrients
• What to do with
leachate?
Composting Process
Feedstock
nutrient & pathogen
influence
WQdifferent
risk
Water content
quality
risk of
Relative risk to
water quality
feedstock.
Ground wood,
bark, fallenof
deciduous
leaves,
woody
yard
Low
Examples
low and
high
risk
feedstock?
debris
Leafy yard debris, horse manure & wood shavings, separated
dairy solids, vegetative crop and pack-house waste
Medium
Mixed food waste, bedding and manure, concentrated
manure, livestock mortalities & slaughterhouse waste
High
Well built piles heat up and decompose quickly, reducing
water quality risk
• C/N: WSU compost mix calculator
• Moisture content: hand squeeze test and oven drying
• Porosity and aeration
The Stages Of Composting
• Composting proceeds in a predictable pattern
that changes as the microbes and food
transform from a fresh to a finished product
• Each stage is approached differently to
optimize the composting process.
Composting process
Waste
Preprocessing
Active Composting
Curing
Four Key Stages of
Composting
Post Processing
Compost
Composting Stages And Phases
Active Stage
• Mesophilic phase, thermophilic phases,
• Decomposition of easily degradable material
• High temperatures are important for pathogen, weed seed kill
Curing Stage
• Mesophilic and psychrophilic phases
• Formation of new long chain compounds called humification
Moisture
• Most microbial activity takes place in thin film of water on surfaces
of organic particles.
• Moisture content too low: poor bacterial activity
• Moisture content too high: anaerobic zones and odor, nutrient
leaching, slower decomposition
• Ideal: 45 - 60% - “wrung-out sponge”
• Typically controlled by adding bulking agents or liquid
Bulk Density
• Relation between Mass / Volume
• Units: kg/m3, lbs/yd3 (conversion factor: approx. 1.7)
•
•
•
•
biosolids  1000 kg/m3 (1,700 lbs/yd3)
sawdust  250 kg/m3 (425 lbs/yd3)
cattle manure 850 kg/m3 (1445 lbs/yd3)
mixed yard waste 400 kg/m3 (680 lbs/yd3)
• Correlated with
• Moisture content (wet weight)
• Porosity
• Particle size and distribution
• Important for
• Calculation of capacities (storage, etc.)
• Handling / transporting
• Indicator of porosity
Feedstock ‘Food’ Quality
Carbon / Nitrogen ratio (C/N ratio)

Too high (> 35): composting process slows, N is tied up

Too low (< 15): N loss (ammonia release)

Ideal starting range for composting: 25 to 35

Depends also on degradability and accessibility of compounds
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N
WSU Compost Calculator
Scroll down
Feedstock “typical” C/N ratio table
Calculates compost Mixtures:
Composting Microorganisms
Factor
Bacteria
Fungi
Carbon/Nitrogen
favor nitrogen
favor carbon
Water
high moisture
low moisture
Oxygen
survive low O2
need > 6% O2
up to 75°C (167°F)
up to 60°C (140°F)
slow at < 5
ok at < 5
faster reproduction
slower reproduction
Temperature
pH
Time
Composting Parameters
• Oxygen
•
Required for aerobic organisms
•
Air in pores is in competition with moisture
•
Particle size, porosity and bulk density affects oxygen in compost
• Moisture
•
Water is required for biological activity
• Temperature
•
Temperature increases to a peak, then begins to decrease during composting
• Chemical Feedstock Properties
•
Nitrogen and carbon, C/N ratio
•
Biodegradability
•
pH
Moisture and Oxygen
Gas transport is faster in pores containing air than in
pores containing water
Microbial Growth and Temperature
Optimum
Temperature
Maximum
Temperature
Minimum
Temperature
0
10
20
30
40
0
50
68
86
104
50
122
60
70
80
140
158
176
Temperature
ºC
ºF
Temperature
• Heat is produced from microbial action
• If temperature low: decomposition will be slow
• If temperature high (> 70oC, [158oF]): some beneficial
microbes will die resulting in reduced diversity
• Temperature needs to above 55oC (131oF) for part of
the time to destroy potential human and plant
pathogens
Compost quality
•
•
•
•
•
•
•
•
Maturity and stability goals
Nutrients
Testing compost at commercial labs
Transformations during composting
Stability testing
Compost suppression of soil borne disease
Long-term impact of compost on soil N
Case study: on-farm compost analyses
Compost maturity and stability
Maturity
• Fitness for a specified use
• No quantitative definition
Stability
• Defined as “resistance to
decomposition”
• Faster decomposition, lower
stability
Problems with unstable compost
•
•
•
•
Odors
Volume shrinkage
Nitrogen “tie-up” or “immobilization” in soil
Pathogens?
Compost quality for different end uses
Field application
Moderate stability/maturity
Low to moderate C:N (want available N)
not too much woody stuff
Mulch
high C:N ok, chunks ok
Potting mix
more stable the better
typical = add 25 % compost by volume (dilute with peat,
perlite/pumice)
avoid high salt (EC), high ammonia (pH > 8)
Yard waste composted 1-week to kill weed
seeds. A hot mulch for rhubarb.
Nutrients in compost
• Feedstock controls nutrients in final compost
• Salts accumulate during composting
• Organic matter is lost as CO2 during composting
• Nitrogen is lost as ammonia gas during composting
• So, if you want high nutrient compost, choose high
nutrient feedstocks,
– or screen out the woody stuff after curing
When sufficient records exist, can estimate “adjustment to soil
N mineralization” using the “decay series approach
Year 1
=available N
2
+
3
+
+
4
+
+
+
5
+
+
+
+
Courtesy Dan Sullivan
N mineralization from compost
PNW composts suppress seedling
damping off disease
Scheuerell et al., 2005. Phytopathology 95:306
Test:
grew vegetable seedlings in pathogen infested media:
compost + peat moss + perlite/pumice
Found:
65% of the compost samples suppressed P. irregulare and P.
ultimum damping-off of cucumber
17% suppressed damping-off of cabbage caused by R. solani.
Solvita test
Calibration: “top of your head” factors
• One cubic yard = 1inch depth on 324 square
feet
• One inch depth
= approx 140 cubic yards per acre
= 70 wet ton/acre
= 35 dry ton/acre
• lb per square foot x 21.78 = ton/acre
Calibration: “top of your head” factors
Compost analysis:
% nutrient x 20 = lb nutrient/ton
ppm nutrient x 0.002 = lb nutrient/ton
1% = 10,000 ppm
% solids (dry matter) + % moisture = 100%
Calibration: “top of your head” factors
One inch application depth (35 dry ton/ac) with 1%
nutrient (20 lb nutrient/ton) in dry compost:
= 700 lb nutrient per acre
Plant available N (PAN)
A inch depth of compost with 2% total nitrogen
= approx 1400 lb total N/acre x 10% PAN
= 140 lb PAN per acre
= 3 lb N/thousand ft2
Balance between nutrient inputs and
plant needs
Plant available N (PAN)
A inch depth of compost with 2% total nitrogen
= approx 1400 lb total N/acre x 10% PAN
= 140 lb PAN per acre
= 3 lb N/thousand ft2
If compost also contains 1% P and 1% K,
= 1400 lb P and K per acre
= 3200 lb/ac P2O5
= 1600 lb/ac K2O
Plant uptake ratio: 1N: 0.1P, 1K