Made available through the University of Manitoba’s natural systems agriculture is a study on grazed green manures.
Legume green manure crops are the foundation of successful organic grain production systems. These crops are able to partner with Rhizobiumbacteria in the soil to fix atmospheric nitrogen (N). When annual legumes are grown specifically for this purpose, they can contribute large amounts of N to the system for use by subsequent crops. In the prairie provinces, a green manure crop is typically required about every third year in order to supply adequate N for other crops in the rotation.
While annual green manures provide important benefits to organic systems, a major factor limiting their widespread adoption is that there is no harvestable product and thus no income from that land in that year. Improving the economics of growing annual green manure crops would make green manuring more financially viable for organic farmers and potentially for conventional farmers as well.
Grazing green manure crops has been suggested as a possible approach to gaining some income from green manure crops while maintaining most of the N benefit to the following crop. Grazing livestock is known to excrete about 80% of the nutrients they ingest; however, little is known about the effects of grazing green manures on nutrient cycling, the agronomic performance of following crops or the economics of such systems.