Composting on Your Small Farm

Jason FauceraClackamas SWCD Conservationist

jfaucera@conservationdistrict.org 503-210-6013

Nick AndrewsOSU Small Farms Horticulturistnick.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

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