The Effect of Grazing and Non-grazing of Annual Green Manures on Following Crops (Year 2)
PCDF
To evaluate the use of an annual green manure crop for grazing by livestock and to
provide fertility for the following crop (2019); and to evaluate the performance of
three annual field crops after a green manure crop, with and without grazing (2020).
The cost of the seed blend for forage is high relative to simpler cereal-only annual forages, such as
barley planted for green feed (estimated at $16.88/ac in the MB Agriculture Cost of Production).
However, some green manure species can provide extended in-season grazing, reducing pressure on
perennial pastures. Strategic inclusion of these species in a green manure mix can improve its
application to grazing. Other management options for green manures and livestock include swath or
bale grazing, which can extend grazing into the winter months, reducing feeding and yardage costs. In
future years, other benefits to soil characteristics, moisture infiltration and retention, and crop
performance may be observed.
The use of green manure crops to provide nitrogen is well-understood in organic agriculture. One of the
barriers to adoption of green manures is that there is no “harvestable” product and no income from that
year. Research conducted by the Natural Systems Agriculture laboratory at the University of Manitoba
has demonstrated that grazing the green manure by livestock can kill the crop, providing an alternative
to terminating the crop with tillage. Further, grazing results in large amounts of available N in the soil.
Follow-up research by the Natural Systems Agriculture laboratory demonstrated that there was no
significant difference in the year-2 crop yield for grazed and ungrazed treatments. The results for that
research suggest that there is no yield decrease associated with grazing a green manure.