Season-long annual grazing systems that supply N to future crops

Integrating legume cover crops or green manures into annual crop rotations has the potential to offer substantial benefits to Canadian prairie cropping systems including N, weed control, and improved soil structure. The price of N fertilizer is increasing and alternative N sources such as green manures may now be more practical for farmers to consider. In Manitoba, green manure systems can consistently enrich soils with at least 100 kg N/ha. However, the challenge of making green manures economically attractive is still an impediment.

Grazing the green manures may be one way around this economic impediment. Research has shown that green manures produce at least as much available N to the subsequent grain crops when they are grazed compared with the standard green manure practice (tilled and no plant material harvested). The green manures tested included pea/oat mixtures, hairy vetch, sweet clover, lentil, soybeans, oats alone, and a mixture (“cocktail”) of various plant species. Based on a green manure production of 5000 kg/ha, animal live weight gain is estimated at 175 kg/ha (Thiessen Martens and Entz, 2011). This translates into $315-481 ha-1 of income from the green manure year.

Integrating legume green manures into annual crop rotations has the potential to offer substantial benefits to Canadian farmers. The price of N fertilizer is increasing and alternative N sources such as green manures need to be considered. In Manitoba, green manure systems can consistently enrich soils with at least 100 kg N/ha. Making green manures economically attractive is still an impediment.

We now know that grazing green manures is one way around this economic impediment. Our previous research has shown that green manures produce 10% more N to the subsequent grain crops when they are grazed compared with the standard green manure practice (tilled and no plant material harvested). Based on a green manure production of 5000 kg/ha (4500 lb/acre), animal live weight gain is estimated at 175 kg/ha (159 lb/acre). This translates into $315-481 ha- 1 ($127-194 acre-1) of income from the green manure year.

April 2013 Update:

Previous research has shown that grazing annual legume green manure crops can provide a valuable product to farmers (i.e. livestock forage) while contributing biologically fixed nitrogen (N) to following crops, thus reducing or eliminating the need for N fertilizer. The challenge presented by such systems is that most annual legume green manures have a rapid growth phase followed quickly by maturity, leaving only a small window of time between adequate biomass accumulation (and associated N fixation) and declining forage quality and palatability. For good utilization of such a grazed green manure, a farmer would require large numbers of livestock for only a few weeks of the summer. Thus, our goal is to develop a system that provides a continuous supply of forage throughout the season while still fixing ample amounts of N. In this way, we hope to design a system that maximizes the value of the green manure year, since no grain crop is harvested during that year.

The objective of this study is evaluate the potential of various annual legume-based systems to provide forage during particular windows of time throughout the growing season, with the twin goals of providing adequate livestock nutrition and adequate N fixation (i.e. at least 100 kg N ha-1). This process begins with examination of various crops and crop combinations to fill specific niches and then combines the information from individual components to develop some flexible and practical options that can be implemented by farmers.

Check back here for details on a planned summer field day.

Project Summary – September 2011
Interim Report – September 2012
Interim Report – April 2013
Project Interim Reporting Guide
MFC XXIV Financial Reporting Template

Researcher: Dr. Martin Entz, U of Manitoba
Start Date:
Fall 2011
Completion Date: