Field Manual
Contents
Bulk Density and Free Air Space
------------------------- 2
Estimating Moisture Content
-------------------------- 5
Building and Monitoring Your Pile
-------------------------- 8
Calibration
-------------------------- 11
Measuring Windrow Volume
-------------------------- 13
Calibration Homework
-------------------------- 14
This Field Manual adapted from other sources by Nick Andrews†, Jason Faucera‡, Kristin Pool†
and Dan Sullivan†
† Oregon
State University Extension
County Soil & Water Conservation District
‡ Clackamas
1
Bulk Density and Free Air Space
Bulk Density
Definition- Mass of a material per unit volume of the material (lbs/yd3)
Ideal Range = 850 lb/yd3 to 1,100 lb/yd3
Why it matters? Bulk Density is linked to
(or 500 kg/m3 to 700 kg/m3)
moisture content and porosity. It is also useful
to estimate storage capacity (ie. How much
space you will need to store your compost/feedstock).
Procedure: To measure bulk density for composting we must simulate the compaction that
occurs in the composting process.
1. Weigh an empty 5 gallon bucket and record the weight.
2. Fill the bucket 1/3 full with material (compost or feedstock). Raise the bucket about 6” above
a firm surface and drop it 10 times.
3. Fill the buck with an additional 1/3 of material. Raise the bucket 6” above a firm surface and
drop it 10 times.
4. Fill bucket level to the brim and raise the bucket and drop it an additional 10 times.
5. Top off the bucket with material and level off- DO NOT DROP.
6. Weigh the full bucket. Record the weight.
7. Complete calculations using the table or equation below.
Bulk Density =
weight of full bucket (lbs) – weight of empty bucket (lbs) x
volume of bucket
conversion
to lb/yd3
2
Easy Bulk Density Calculation Using a 5 gallon Bucket
A
Material
Example
Weight of
empty 5 gal
bucket (lb)
2.0
B
C
Weight of full
compacted 5
gal bucket (lb)
Weight of
compacted
material (A - B)
20.5
18.5
D
BULK
DENSITY
(C x 40)
740
Workspace/ Notes:
3
Free Air Space
Target Free Air Space is 60% and NO less than
Definition: The volume of space in a material that is not occupied by particles or water.
35% of the total volume
Why it matters? Adequate free air space ensures an oxygen supply for the microorganisms.
Procedure: In this test water is used to estimate the amount of free air space in the material.
1. Use the bucket filled with compacted material from the bulk density procedure. Place the
full bucket on level ground.
2. Fill the bucket with water completely without overflowing.
3. Weigh the bucket and record the weight. Be Careful as the bucket will be very heavy!
4. Complete the calculations using the equation or table below.
Free Air Space =
Weight of bucket with material and water - weight of bucket with material
weight of bucket full of just water – weight of empty bucket
x 10
Easy Free Air Space Calculations Using a 5 gallon Bucket
A
B
C
D
Material
Weight of full
compacted 5
gal bucket (lb)
Weight of full
compacted 5
gal bucket with
water (lb)
Weight of
Water (B – A)
Free Air Space
% (C x 2.4)
Example
20.5
46.5
26
62%
*The above table operates based on the calculation that 5 gallons of water weighs 42 lbs.
4
Hand-Squeeze Quick Test for Pile Moisture
Goals for this activity:


To learn the “hand squeeze” method for estimating moisture levels in a compost pile.
To practice estimating moisture in composting materials
After a certain amount of practice your hand becomes “calibrated” allowing you to evaluate
moisture without other equipment.
The hand squeeze method is good for quick tests out in the field, but should not replace periodic
drying tests.
Procedure for Hand-Squeeze Moisture Test
(1) Reach into the pile (bucket) and grab a handful of composting material.
(2) Squeeze the material hard, check for drips.
(3) Release your grip and allow the material to stay in your hand, smear some between
your finger and thumb.
(4) Inspect the material and your hand.
(5) Use the “Rules of Thumb” to estimate % moisture.
(6) Record your observations and your own % moisture estimate.
(7) Talk to your group and reach an agreement for a group estimate.
(8) Record Results.
(9) Repeat the test for each of the available materials.
5
Interpretation – “Rules of Thumb” for Estimating Moisture
Observations
% Moisture
(Estimate)
Material feels dusty
42 % or less
Material feels mostly dry with a hint of moisture
42% - 47%
Material feels tacky and sticks together
47% - 52%
Material feels moist, but no water comes out
52% - 58%
Material leaves a wet sheen on hand
58% - 63%
If one to two drops of water come out during squeezing
63% - 68%
If many drops of water come out during squeezing
68% - 73%
Stream of water from material when squeezed or pudding texture
73% or more
Estimating % Moisture
Bucket
Number
Observations
My
Estimate
Group
Estimate
%
Moisture
%
Moisture
6
Determining Feedstock Moisture with Koster Dryer or Oven
Determining feedstock moisture with a dryer requires a scale accurate to about 1 gram. The
Koster Dryer comes with a mesh bottomed container in which to place the sample to be dried.
Drying times depend on the feedstock and the moisture present in the sample at the time of
drying. Follow the steps below and enter the results on the worksheet to determine the %
moisture of the sample. If drying in an oven, set temperature at lowest setting and leave door
ajar to avoid burning the sample.
Line
1
2
3
4
5
6
Weight
Instructions
Container
tare weight
Wet weight
& container
Wet weight of 200-300 gram sample
with container
Sample wet
weight
Calculation:
line 2 – line 1
260 g
Dry weight &
container
Weigh once, dry sample for 10 more
minutes and reweigh. Final weight
must be the same in 2 measurements
126 g
Sample dry
weight
Calculation:
% dry weight
Calculation:
% moisture
Your
values
40 g
line 4 – line 1
line 5 ÷ line 3 x 100
7
Example
300 g
86 g
33%
Calculation:
100 – line 6
67%
7
Building and Monitoring Your Pile
Feedstock Data
%
Moisture
Total N
(%)
Total C
(%)
C/N
Ratio
Bulk
Density
Parts in
Your Mix
Chicken
Manure
Horse
Manure
Yard
Debris
Vegetable
Waste
Spoiled
Wheat
Wood
Chips
Dairy
Solids
8
Pile Characteristics and Monitoring Records
Actual Pile Recipe
Feedstock
# of 5 gallon
buckets
# of
wheelbarrows
Parts in Mix
Bulking Agent
Water (gallons)
Pile Design Notes (i.e. pad, aeration, etc.)
9
Pile Characteristics and Monitoring
Team Name:
Date /
Time
%
Moisture
C/N ratio
Bulk
Density
(lb/yd3)
Free Air
Space
Temp
Edge
Temp
Middle
Other Pile Notes (from team and class evaluations):
10
Calibration
Determining Nutrient Application Rate
Example: I am growing sweet corn and the nitrogen recommendation is 100 pounds N per
acre. I have beef manure that has been tested by a laboratory and contains 11
pounds of N, 2.2 pounds of P, and 8.3 pounds of K per wet ton of manure.
Note: Unshaded cells are information about manure and crop. Shaded cells are calculations you make.
Line
Step
1
Type of manure or compost
2
Crop
3
Desired N application rate
4
Units
Example
Your Value
Beef
manure
Sweet
corn
lb N/acre
100
Manure N concentration, from
laboratory analysis
lb N/ton asis
11
5
Phosphorus concentration from
laboratory analysis
lb P/ton asis
2.2
6
Potassium concentration from
laboratory analysis
lb K/ton asis
8.3
7
Plant availability of N in compost or
manure (from OSU fertilizer calculator)
Percent
25
8
Calculate available N:
line 4 x (line 7 ÷ 100)
lb N/ton asis
2.75
9
Calculate application rate:
line 3 ÷ line 8
Tons/acre
as-is
36
10
Calculate amount of phosphorus
applied:
line 9 x line 5 x 2.3
lb P2O5/acre
184
11
Calculate amount of potassium applied:
line 9 x line 6 x 1.2
lb K2O/acre
362
11
Calibrating Spreader to Apply a Specific Rate
Line
Formula
Ex.
Your
Calibration
Step 1. Calculate
spreader capacity
1.1
1.2
1.3
1.4
1.5
Weight of empty spreader
vehicle (lb)
Weight of spreader vehicle
loaded with compost (lb)
Weight of compost in
spreader vehicle (lb)
Total solids analysis of
compost (percent)
Dry weight of compost (dry
ton per full spreader load)
12000
30000
line 1.2 - line 1.1
18000
20
(line 1.4÷100 * line 1.3) ÷
2000
1.8
Step 2. Calculate
compost application rate
on an "as-is" basis
2.1
2.2
List target compost
application rate (dry ton/acre)
Calculate target compost
application rate (wet
ton/acre)
3.0
line 2.1 * 100 ÷ line 1.4
15
line 1.5 ÷ line 2.1 x 43,560
26136
Step 3. Calculate feet of
travel for a full spreader
load
3.1
3.2
3.3
Calculate target area to
cover per spreader load (ft2)
Measure width of spreader
application swath (ft)
Calculate feet of travel for
application of full spreader
load (ft)
20.0
line 3.1 / line 3.2
1307
Step 4. Calculate the
number of spreader
loads to apply per field
4.1
4.2
List net acreage available for
compost application
(acres/field)
Calculate number of
spreader loads to apply per
field
30.0
line 4.1 *43560 / line 3.1
50.0
12
Windrow Volume

Area of a triangle


Area of a windrow = area of triangle * length
1 yd3 = 27 ft3
Line Measurement
Example
1
Height (ft)
4 ft
2
Width (ft)
8 ft
3
Area of triangle (ft2):
(line 1 * line 2) ÷ 2
16 ft2
4
Length (ft)
50 ft
5
Area of windrow (ft3):
Line 3 * line 4
800 ft3
6
Area of windrow (yd3):
line 5 ÷ 27
29.6 yds3
7
Bulk density
920 lbs/ yds3
8
Weight (lbs):
(line 6 * line 7)
27,232 lbs
9
Weight (tons):
(line 7 ÷ 2000)
13.6 tons
Your windrow
13
Week 2 Compost Workshop Calibration Questions
Dan Sullivan, OSU
Instructions: Knowing your application rate is an important part of using compost on the farm. Try your
hand at these calculations. These problems require unit conversions. See last page of this handout for
list of conversion factors. PNW Extension publication 533 also provides a variety of approaches to
calibration (see Table 3 and Worksheets A, B, and C).
Reference:
Fertilizing with Manure. PNW Extension publication 533.
http://cru.cahe.wsu.edu/CEPublications/pnw0533/pnw0533.pdf
1. A compost contains 20,000 ppm N on a dry weight basis. The “as-is” (wet) compost contains 50%
dry matter and 50% moisture. The “as-is” compost contains:
10 lb N per wet ton
5 lb N per wet ton
40 lb N per wet ton
20 lb N per wet ton
2. A compost contains 20,000 ppm N on a dry weight basis. On a dry weight basis, this compost
contains:
20 lb N per dry ton
10 lb N per dry ton
80 lb N per dry ton
40 lb N per dry ton
14
3.
An extension agent lays out a tarp in the field to catch compost from a compost spreader. After
the spreader has applied compost to the field, 50 lbs of compost are present on a 6 x 6 ft tarp. The
compost application rate is:
30 tons per acre
60 tons per acre
3 tons per acre
12 tons per acre
4.
A farmer loads 12000 lb of compost in a compost spreader. The compost spreader is empty after
an area of 24000 square feet has been spread in the field. The compost application rate is:
14 tons per acre
11 tons per acre
18 tons per acre
20 tons per acre
5.
A farmer uses a compost spreader that holds a volume of 130 cubic feet of compost. The compost
has an estimated bulk density of 1000 lb per cubic yard, and a full spreader load covers
approximately 6000 square feet in the field. The approximate compost application rate is:
18 tons per acre
36 tons per acre
1.8 tons per acre
3.6 tons per acre
6. A market vegetable gardener applies 25 five-gallon buckets of compost to a garden area of 1000 square
feet. The compost has a bulk density of 4 lb per gallon. The estimated compost application rate is
50 lb per thousand square feet
250 lb per thousand square feet
500 lb per thousand square feet
600 lb per thousand square feet
15
7. A compost contains 20 lb total N per “as-is” (wet) ton, and approximately 10% of the total nitrogen is
estimated to become plant-available during the first growing season following application. To supply 50
lb of plant-available N for the first growing season, compost should be applied at the rate of:
5 ton/acre
10 ton/acre
20 ton/acre
25 ton/acre
8. A compost contains 0.5% phosphorus (P). This compost is applied at the rate of 10 tons per acre. The
amount of phosphate (P2O5) applied is
230 lb P2O5 per acre
100 lb P2O5 per acre
50 lb P2O5 per acre
200 lb P2O5 per acre
Bonus question: Twenty one soil scientists are laid end to end. Will they reach a conclusion?
16
Conversion Factors
Measurement
Unit
Symbol
Multiply by
To obtain
Symbol
Weight
ton
lb
2000
pound
lb
Area
acre
acre
ac
ac
43560
43.56
sq ft or ft2
thousand ft2
ac
ac
Volume
gallon
cubic yard
gal
yd3
8.35
27
pound
cubic feet
lb
ft3
Concentration
parts per million
percent
percent
ppm or mg/kg
%
%
0.002
20
10000
pound/ton
pound/ton
parts per million
lb/ton
lb/ton
ppm
Dry or wet
percent dry matter (total solids)
percent moisture
compost, dry wt. basis
% DM
% moisture
0.01
0.01
100/(%DM)
solids, decimal fraction
moisture, decimal fraction
compost, "as-is" basis
DM
MF
Rate
lb per square ft
lb/ft2
21.78
ton/acre
ton/ac
Nutrients
phosphorus
potassium
nitrogen in nitrate form
nitrogen in ammonium form
nitrogen in organic form
P
K
NO3-N
NH4-N
org-N
2.29
1.20
1
1
1
phosphate
potash
nitrogen
nitrogen
nitrogen
P2O5
K2O
N
N
N
Calibration worksheets available in:
Fertilizing with Manure. PNW Extension publication 533.
http://cru.cahe.wsu.edu/CEPublications/pnw0533/pnw0533.pdf
17