Chicken manure and soil science

Did you ever wonder how much
of the nutrient content from that bag of chicken feed ends up in the
soil?  Or how many chickens you’d need to fertilize a perfect
lawn?  Joseph Heckman is a soil scientist and chicken aficionado
who did the math so we don’t have to.



Those of you who garden
are probably familiar with N-P-K — the percent of nitrogen,
phosphorus, and potassium in a fertilizer.  For example, the compost
we bought from a nearby chicken farm has an N-P-K of 3-4-4, which
means it contains 3% nitrogen, 4% phosphorus, and 4% potassium.



An average bag of chicken
feed has an N-P-K of 2.66-0.6-0.84, but those nutrients don’t all end
up in the soil.  Some of the nutrients are converted to eggs, some
are used by the hen to keep herself going, and she only excretes what’s
left over.  You can read
through the math, or
just take Heckman’s word for it that each of your chickens enriches the
soil by 2.48 pounds of nitrogen, 0.63 pounds of phosphorus, and 0.93
pounds of potassium over the course of a year.



Heckman goes on to note
that lawn fertilizer recommendations are for around 87 pounds of nitrogen
per acre per year.  You’d need 35 chickens per acre to provide
that amount of nitrogen, or, looking at it another way, would want to
give each laying hen 1,263 square feet to make sure the lawn could suck
up all of the nutrients being pooped out by your flock.



Although chicken manure
is a high quality fertilizer, it’s possible to get too much of a good
thing.  Heckman recommends testing your soil at intervals if
pastured chickens are your primary method of fertilization since
phosphorus and potassium can eventually build up to unhealthy levels
from their rich manure.  I highly recommend Harvey Ussery’s The
Small-Scale Poultry Flock to help you come up with ideas on diversifying
your homestead’s fertilizing campaign while still using chickens as
the centerpiece.



The photos in this post
come from a
post about Joseph Heckman’s farm.  Thanks for letting me
share your information!