“THE SOIL LIFE WILL MAKE A MAJORITY
OF THE NUTRIENTS AVAILABLE THE FIRST
YEAR, WITH THE REST FEEDING THE PLANTS
OVER THE NEXT ONE OR TWO YEARS.”
Nutrient Availability
Fresh vs. Composted Manure
Fresh manure can cause more problems than it solves, so
composted manure is generally recommended. However, you
can use fresh manure if you take certain precautions.
Fresh manure contains high levels of ammonium, or
soluble nitrogen, compared to composted manure. Poultry
manure, specifically, will likely cause nitrogen burn in
plants if it has not been composted. Fresh manure must
be incorporated six to eight inches deep within 12 hours of
application, or else the majority of the ammonium will be
released into the atmosphere.
Fresh horse manure is notorious for containing weed seeds,
which can lead to major weed problems in your garden.
Human pathogens are easily transmitted through fresh
manure. E. coli, Salmonella, Campylobacter bacteria, and
Giardia or Cryptosporidium protozoa can live in manure
and contaminate crops. For this reason, organic standards
dictate fresh manure must be applied 120 days before
planting to give pathogens time to die off.
You can avoid these issues by using composted manure.
To guarantee harmful pathogens have been killed, the
compost pile must reach 131-140°F degrees for several
weeks. The pile must be turned regularly to ensure all the
manure had been exposed to hot enough temperatures.
Many commercial operations will pasteurize their compost
to destroy pathogens, however, beneficial microorganisms
are also killed in the process.
64
Maximum Yield
While you can estimate the nutrients available in manure,
the only way to get an accurate analysis is testing it in a
lab. When collecting your sample, be sure to collect several
subsamples and mix them together to get the most accurate
results.
If you are buying your manure
commercially, you can request
the nutrient analysis from
the seller for nitrogen (N),
phosphorus pentoxide (P 2 O 5 ),
and potassium oxide (K 2 O)
content. The analysis will
show you the nutrient content,
but availability depends on
the microorganisms in your
soil breaking the nutrients
down into a form plants can
use.
If you don’t want the
expense of lab tests,
you can approximate
the nutrient content. For
example, the Livestock
Waste Facilities Handbook
says horse manure with
bedding will contain four pounds/ton of soluble, or
readily available, nitrogen, and an additional
10 pounds/ton of organic nitrogen that still needs to be
broken down by microbes. It will also contain about
four pounds/ton of P 2 O 5 and 14 pounds/ton of K 2 0.
Composted poultry manure will contain about
one pound/ton of soluble nitrogen, 16 pounds/ton of organic
nitrogen, 39 pounds/ton of P 2 O 5 , and 23 pounds/ton of K 2 O.
You can compare that to fresh poultry manure without
bedding, which is estimated to contain 26 pounds/ton
of soluble nitrogen, seven pounds/ton of organic nitrogen,
48 pounds/ton of P 2 O 5 , and 34 pounds/ton of K 2 O.
While fresh manure can contain too much nitrogen
for the garden and burn plants, composted manure
contains organic nitrogen which is not available to
plants until microbes convert nitrogen to ammonium
(NH 4 ). This occurs over years.
Typically, 25-50 per cent of the manure’s nitrogen will
be available the first year, with less being available
each subsequent year. In general, 70-80 per cent of the
phosphorus (P) and 80-90 per cent of the potassium
will be available the first year.
If you get manure that contains bedding, it is important
to be aware of the carbon to nitrogen ratio (C:N) in the
manure. If the ratio exceeds 30:1, the nitrogen will be tied
up temporarily while it helps the carbon break down. If
this is the case, you may need to add nitrogen fertilizer to
your plants until the nitrogen in the manure is released.