Top Crop Manager

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Will cover crops work for you?

Farmers harvest sunshine


November 13, 2007
By Ken Janovicek Bill Deen Greg Stewart Ian McDonald Peter Johnson and Adam Hayes

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Farmers harvest sunshine. After the wheat crop is harvested, there are at least
two months of brilliant sunshine still to come. Yet, often this sunshine falls
on bare ground. There must be a way that farmers could harvest this sunshine
to improve their soil and bottom line.

Three years of trials (2003 to 2005) in southwestern Ontario have shown that
cover crops after wheat can produce significant plant biomass. These plots showed
various cover crops captured significant nitrogen in their plant material, and
greatly reduced late fall soil nitrogen levels. All of the soil health parameters
should improve: increasing organic matter, water infiltration and water holding
capacity, and reducing soil erosion potential.

Eighteen research/demonstration plots were established following winter wheat
harvest over this three year period. Cover crop species included annual ryegrass,
buckwheat, oats, oilseed radish and peas. Red clover was evaluated at several
of the sites. Manure (swine, liquid dairy, or solid cattle manure) and non-manure
treatments were also evaluated at each site.

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Biomass production is increased with manure
Figure 1 shows the biomass production of each cover crop expressed relative
to oat biomass production. In the absence of manure, oats performed better than
annual ryegrass, buckwheat and oilseed radish, while peas and red clover out
paced oats for biomass production. Manure applications increased growth by 50
percent or more, except for the pea cover crop.

Nitrogen
Figure 2 illustrates the amount of biomass nitrogen that was trapped by the
oats, oilseed radish and pea cover crops. Without manure, the peas had the highest
levels of plant biomass nitrogen, significantly higher than oilseed radish or
oats. With manure, the peas showed little increase in plant biomass nitrogen,
but the oilseed radish and oats had significant increases in plant biomass nitrogen.

Figure 3 shows the impact of cover crops on soil nitrogen levels in the fall.
The value of the cover crops was most evident where manure was applied. The
soil nitrogen levels where no cover crop was planted showed significantly more
fall soil nitrogen available than where any of the cover crops were established.
The oats and oilseed radish reduced the late fall soil nitrogen levels significantly.
Peas did not draw down soil residual nitrogen levels like the other cover crops,
likely due to its nitrogen fixing abilities as a legume crop.

The biomass bottom line
Cover crops are excellent at capturing nitrogen and building biomass. The final
piece of this puzzle asks: does a cover crop increase yield, or reduce nitrogen
requirements, in the following corn crop? The jury on these questions is still
out. With harvest of the corn plots from our sites in 2006, we hope to have
the answer, which we will report in a winter issue of Top Crop Manager!

*Ken Janovicek, Bill Deen of the University of Guelph and Greg Stewart,
Ian McDonald, Peter Johnson, Adam Hayes of the Ontario Ministry of Agriculture,
Food and Rural Affairs. This project was funded by Agriculture and Agri-Food
Canada via the Greenhouse Gas Mitigation Program for Agriculture, administered
by the Soil Conservation Council of Canada. The project was a co-operative effort
between the University of Guelph and Ontario Ministry of Agriculture, Food and
Rural Affairs' crops staff, in conjunction with Ontario Soil and Crop Improvement
Association and Innovative Farmers Association of Ontario.