MULTI SPECIES PASTURE – BIOLOGICAL NITROGEN CAPTURE Biological nitrogen fixation is a complex process. Put simply, all plants, including forage crops, need relatively large amounts of nitrogen (N) for healthy growth and development. Biological nitrogen fixation (BNF) is the term used for a process in which nitrogen gas from the atmosphere is incorporated into the tissue of certain plants. Only a select group of plants can obtain N this way, with the help of soil microorganisms. Among forage plants, the group of plants known as legumes (Fabaceae family), are well known for being able to obtain N from air. A few common legumes available in Tasmania that can be incorporated into existing pasture systems are peas, beans, clovers and lucerne. Brassicas are also well suited to capturing nitrogen.
In forage production, this process can be very important because it means that the muchneeded N can be obtained from three sources: the atmosphere via BNF, the soil, and from fertilisers. Forage producers who find ways to maximise the amount of N obtained from the atmosphere via BNF will be able to reduce their fertiliser costs while maintaining soil fertility, high levels of forage protein, and high yields. The process by which some forage crops can incorporate N from the air into their tissues involves a symbiotic (mutually beneficial) relationship. For example, Lucerne is the host plant to a microorganism that is associated with BNF. With most forage crops the second organism is a bacterium that occurs naturally in the soil, known as rhizobia.
Nodulation on Tic Bean
These soil bacteria infect the roots of the plant and form nodules (see image on right). The chemical reactions, that is the process known as BNF, take place in the nodules. So, with rising cost in fertiliser, now is a time to reset and consider diversifying that common Rye Grassdominant pasture by adding multiple species into the system, not only for nitrogen fixation, but for soil and stock health benefits. Consult your local seed supplier for options to consider or contact Ali Dugand – Agriculture Project Coordinator – adugand@cradlecoast.com
Multi-species pasture p. 10
