about how much of each to mix to get the moisture con-
tent and the C:N into reasonable ranges so the process
can get off to a good start. One example is given in the
box “A Sample Compost Recipe” on p. 142.
Cornell University’s website for composting issues
(http://cwmi.css.cornell.edu/composting.htm) features
formulas to help you estimate the proportions of the
specific materials you might want to use in the compost
pile. Sometimes it will work out that the pile may be too
wet, too low in C:N (that means too high in nitrogen),
or too high in C:N (low in nitrogen). To balance your
Figure 13.1. On-farm composting facility, in which tarps are used to con-pile, you may need to add other materials or change the
trol moisture and temperature. The piles in the background are curing.
ratios used. The problems can be remedied by adding
dry sawdust or wood chips in the first two cases or nitro-
difference between the C:N calculated with total carbon
gen fertilizer in the third. If a pile is too dry, you can add
and calculated with only biodegradable carbon.
water with a hose or sprinkler system.
It’s important to avoid using certain materials such as
One thing to keep in mind is that not all carbon is
coal ash and especially wood chips from pressure-treated
equally available for microorganisms. Lignin is not eas-
lumber. And it’s a good idea to go easy using manure
ily decomposed (we mentioned this when discussing soil
from pets or large quantities of fats, oils, or waxes. These
organisms in chapter 4 and again in chapter 9, when we
types of materials may be difficult to compost or result in
talked about the different effects that various residues
compost containing chemicals that can harm crops.
have when applied to soil). Although some lignin is
Wood chips or bark is sometimes used as a bulking
decomposed during composting—probably depending
agent to provide a “skeleton” for good aeration. These
on factors such as the type of lignin and the moisture
materials may be recycled by shaking the finished com-
content—high amounts of carbon present as lignin may
post out of the bulking material, which can then be used
indicate that not all of the carbon will be available for
for a few more composting cycles.
rapid composting. When residues contain high amounts
of lignin, it means that the effective C:N can be quite
Pile Size
a bit lower than indicated by using total carbon in the
A compost pile or windrow (figure 13.1) is a large,
calculation (table 13.1). For some materials, there is little
natural convective structure—something like many
Table 13.1
Total vs. Biodegradable Carbon and Estimated C:N Ratios
Material
% carbon
c:N
% carbon
c:N
% lignin
% cell Wal
% Nitrogen
(Total)
(biodegradable)
Newsprint
39
115
18
54
21
97
0.34
Wheat straw
51
88
34
58
23
95
0.58
Poultry manure
43
10
42
9
2
38
4.51
Maple wood chips
50
51
44
45
13
32
0.97
Source: T. Richard (1996a).
143
Building SoilS for Better CropS: SuStainaBle Soil ManageMent