Page 14 - MWC 2-24-2022s

The Midwest Cattleman · February 24, 2022 · P14
LET LEGUMES PROVIDE
YOUR NITROGEN

By Jim Gerrish
Many years ago, I heard the or sheep have over the last
definition of an agronomist half century.
as being someone who never Our pastures need nitrogen
ceases to be amazed that ni- to grow, and our livestock gain
trogen (N) makes grass grow. their protein from the N con-
Throw a little N on a pasture, tained in pasture plants. If we
and it turns green and grows don’t buy N fertilizer, where do
faster. Throw a lot of N on a we get that needed N?
pasture, and it gets darker Another way
green and grows even faster. The answer is very simple
Of course, there is a limit as and has been right in front of
to how dark the grass can get us for centuries. Our prima-
and how fast it can grow. ry source of N for pastures
There is also an economic
cost to every added pound of should come from the legumes
growing in that pasture.
N on the farm. Nitrogen is the There are many producers
most transient element in the in every part of the U.S. who
ecosystem. We may buy a hun- rarely or never purchase N
dred units of N fertilizer in the fertilizer. While some give up
spring, but N is always subject productivity because they do
to movement and loss from nothing to bring N into the
our pasture. pasture, there are others who
Microbial denitrification rely on having a healthy le-
converts soil N into gases that gume component in their pas-
escape into the atmosphere. tures and give up no produc-
Groundwater movement tivity compared to N-fertilized
leaches N below the rooting grass pastures. As a bonus, in-
profile. A cow eats grass, then dividual animal performance
urinates, and N leaves the is almost always higher on a
urine puddle as ammonia. Our grass-legume mix compared to
N investment vanishes quick- a straight grass pasture.
ly from the land. By the time Over the course of the 22
fall rolls around, we generally years we were on our farm
have lost well over half of our in Missouri, there were three
spring N application. occasions on which we pur-
Because of the transience
of N, there is also an envi- chased N fertilizer. Those
were for very specific reasons,
ronmental cost as it leaves and it was applied to no more
the pasture. This includes ni- than 25% of our pasture acres.
trates in groundwater, nitrous We relied on N fixation by the
oxide and ammonia in the at- legumes in our pasture, even
mosphere, and algal blooms urine distribution through
in surface ponds, lakes, and high stock density grazing,
streams, resulting in fish kills. and building organic matter
Buying commercial N fer- in the soil to provide N.
tilizer is not a paying proposi- Our target is to have 30%
tion for most livestock opera- to 50% of the pasture forage
tions. It hasn’t been for most production come from legume
of the past 30 to 40 years due growth. With this much le-
to the changing relationship gume production, we expect
between input costs and live- the equivalent of 100 to 150
stock value. The cost of fertil- units of N to be generated
izer has risen at a much faster through N fixation annually.
rate than the value that cattle Because we are grazing
livestock and not harvest-
ing hay, most of that N is
being returned to the soil
through urine and dung.
It is our job to manage
the pasture in such a way
that a high percentage of
the N is held in the soil
and not lost to ammonia

continued on page 32