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Composting on Your Small Farm
Jason FauceraClackamas SWCD Conservationist
[email protected] 503-210-6013
Nick AndrewsOSU Small Farms [email protected] 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
Soil Amendment
Healthy Soil Healthy Crops
High Quality Food and
Forage
Crop & Livestock
Waste Closed Nutrient
Cycle
Compost topics1. Site selection2. Composting methods3. The composting process4. Compost quality and testing5. Compost application
Site Selection & Design: 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
Method Cost PFRP Duration Turning frequency
Windrow – loader
Minimal added investment
May not be consistently met
6-12 mo 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
Smoky Hills Farm & O2 CompostMarc Anderson
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
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
Water quality risk of different feedstock. Examples of low and high risk feedstock?
Feedstock nutrient & pathogen content influence WQ risk
Relative risk to water quality
Ground wood, bark, fallen deciduous leaves, woody yard debris
Low
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
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
Active Composting
Curing
Compost
Preprocessing
Post ProcessingFour Key Stages of Composting
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
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCC 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
Temperature up to 75°C (167°F) up to 60°C (140°F)
pH slow at < 5 ok at < 5
Time faster reproduction slower reproduction
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
0 10 20 30 40 50 60 70 80 ºC0 50 68 86 104 122 140 158 176 ºF
Gro
wth
Rat
e
Temperature
Minimum Temperature
Optimum Temperature
MaximumTemperature
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 stabilityMaturity• 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 applicationModerate stability/maturityLow to moderate C:N (want available N)not too much woody stuff
Mulchhigh C:N ok, chunks ok
Potting mixmore stable the bettertypical = 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
2
3
4
5
available N
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 cucumber17% 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/ton1% = 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