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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

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