OF Dec Jan 2020

Creating the
Optimum Compost
Proper Feedstocks and Treatment Are Essential for a Beneficial Blend
BY TAYLOR CHALSTROM, Editorial Assistant Intern
Compost offers a wide range of
benefits to soils depending on the
blend, providing soils with biomass,
carbon and nitrogen sources.
In order for compost to work in a soil, it
needs to have the proper blend of feedstocks
and be tested/treated to ensure
proper nutrient levels and microbial activity
are present. This article provides
insight into the large-scale compost
operation at Cal Poly, San Luis Obispo,
and how this compost provides benefits
to a nearby vineyard.
Finding the Right Mix
Kevin Piper, Director of Agricultural
Operations at Cal Poly, San Luis
Obispo, said in recent video interview
that the school’s own operation takes
four key components into account
when building the feedstocks that go
into their compost: carbon to nitrogen
(C:N) ratio, percent moisture, bulk
density (measured in cubic yards) and
texture.
“Good composting practices are important,”
Piper said. “We want to know
our feedstocks well, and that means
knowing the specific components of
each.
“Texture is a good thing to incorporate,
and normally you’re going to get that
with your carbon source,” he continued.
“This could be anything from fine sawdust
all the way up to rough woodchips.
You want to find a happy medium; if
you have too much fine texture, you’ll
end up with a light mix that has a hard
time holding temperatures, and if you
have too much rough texture, you’ll
end up with a density issue.”
The Organic Compost page on Cal
Poly’s website (cafes.calpoly.edu/cal-poly-compost)
says that the school’s
operation removes solid manure from
its dairy, beef, equine and poultry units
and incorporates it with green waste
from campus landscaping to create its
unique blend. The specific feedstock
breakdown for the operation, according
to Piper, is green waste (55% moisture,
610 lbs/cu yd., C:N ratio of 150,) waste
feed/silage (75% moisture, 1,300 lbs/
cu yd., C:N ratio of 12,) horse manure
(45% moisture, 450 lbs/cu yd., C:N ratio
of 40) and separated solids from the
on-campus dairy operation (85% moisture,
1,400 lbs/cu yd., C:N ratio of 18.)
“Once we’ve blended our recipe, we
want our ideal component ranges to be
a bulk density of 800 to 1,000 lbs/cu yd.,
40 to 60% moisture and a C:N ratio of
30,” Piper said.
Best Practices for Compost
Creating a compost blend can be a
complicated and drawn-out process
and there are several safety/sanitation
measures to keep in mind. If a compost
producer’s operation is as large as Cal
Poly’s, which Piper said produces 7 to
8 million pounds of manure annually
that is then turned into about 3,000 to
3,500 cubic yards of finished compost,
vigorous sanitation steps and testing
are necessary to retain organic certification.
“Compost producers have to consider
California’s regulatory environment,”
Piper said. “In this state, we deal with
CalRecycle and the Regional Water
28 Organic Farmer December/January 2020