Substituting Legumes for Fallow in U.S. Great Plains Wheat Productions
1) Through small-plot research, explore the suitability of alternative legumes as a key feature in
developing new crop and livestock management systems which will successfully substitute for
fallow in the spring and winter wheat regions of the U.S. Great Plains.
2) To research and demonstrate the on-farm suitability of legumes and crop-legume systems
which best perform at the small-plot scale and in innovative farmers’ fields in the spring wheat
region of North Dakota and the winter wheat area of Nebraska.
Evaluation of alternative legumes was conducted at the experiment stations at Carrington, North
Dakota, North Platte, Nebraska, and Tribune, Kansas. A total of approximately 42 legume
species were studied, and 20 species were included in detailed experiments. Data was collected
on biomass yield, nitrogen content, water use, effect on soil nitrogen status, and effect on yield
and quality of subsequent cash crops. On-farm trials were conducted at 18 cooperating farms, all
located in North Dakota.
Of the 42 legume species evaluated to date, yellow-blossomed sweet clover, hairy vetch, foxtail
dalea, and black lentil proved to have the greatest immediate promise. While seedling
establishment was most reliable from those species with larger seed, under current markets the
cost of using theses species is generally prohibitive. Alternative approaches to legume
establishment, conducted mostly in on-farm trials, demonstrated that adapted broadleaf crops
(such as the oilseeds sunflower, crambe, safflower, and rapeseed) provide the best opportunity to
establish the legume as a companion crop.
The reasons for legume success in these systems include compatibility with the growth habit of
the oilseeds, tolerance of common herbicides used with the oilseeds, and the motivation of the
farmers themselves to experiment with cover crop establishment. A potential barrier to adoption
of substituting legumes for fallow is the possibility of soil moisture depletion. This project has
demonstrated, through rotational small and large plot trials, that there are legumes and
management approaches effective in transforming evaporative water loss (from black fallow)
into transpirational water loss (through legume fallow). Systems which reduce evaporative
demand from the vegetative cover, increase snow retention and capture, and various cultural
practices including early legume termination, haying or grazing, have all been successful in
contributing towards water conservation during the legume fallow.
On March 8, 1991, a meeting was held to discuss with all interested farmers the topic of
interseeding sweetclover in row crops. Three farmers who had successfully interseeded
sweetclover into sunflowers and corn were there to share their experiences. As a result of the
meeting, seven farmers, in addition to five others who had already been cooperating with this
project, decided to try the practice. Out of these 12, eight had good or partial catches. It is
believed that methods can be improved to increase the success rate; however, for many farmers
the success rate need not be high as long as it remains an inexpensive and relatively easy
Perhaps the greatest contribution of this project will be the transformation of at least a portion of
the wheat growing Great Plains from traditional black fallow practices to that of a soil-building
legume fallow. Such a transformation would decrease soil erosion and reduce herbicide loading,
contribute nitrogen to the cropping system, thereby reducing dependency upon nitrogen
fertilizers, and help reverse the degradation of soils by periodically incorporating organic matter
through legume production.