b'COVER CROP CORNERWHY COVER CROPS ARE ONE OF NATURES NITROGEN SOURCESNITROGEN IS ONE of the largest expenses onhosts for mycorrhizal fungi, which is always most farms and plants respond quickly toa good thing. A living plant in the vegeta-additions and deficiencies in the field. Yet intive stage is also a positive option, tying up areas that we are not farming, plants seem tofree nutrients and releasing root exudates to be growing and thriving without additions ofstimulate soil biology and creating good soil synthetic fertilizer. What is happening? structure. Including legumes in the mix will In native plant stands, being either grass- ensure there are plants with nitrogen-fixing based or treed, plant growth seems to berelationships with rhizobium. This is impor-Kevin Elmy adequate to cover the ground and producetant as the legume nitrogen fixation tends to Elmy is founder of Coveraboveground biomass. Where do thesebe greater in an agricultural system than the Crops Canada. His booknutrients come from? Nature has evolvedfree-living microbes by themselves. Cover Cropping in Westernover centuries to have an elaborate systemThe reason synthetic nitrogen is used over Canada is availableof plants capturing sunlight through photo- biological nitrogen is predictability. Sir Albert through Friesen Press,synthesis creating sugars that the plant canHoward saw this back in the early 1900s; Amazon, and digitallyuse for plant growth and as exudates to feedfarmers wanted the easy button even though through Apple Books,microbes on the leaves, stems and roots. Thesynthetic nitrogen applications turn out to be Kindle, and Google Play.exudates released through the roots feed soilonly 50 per cent effective in most cases.For more info on Covermicrobes that will in turn free up soil-boundBut because agronomists are trained with Crops Canada visitnutrients for the plants.traditional soil tests, nitrogen supply is deter-covercrops.ca There are free living nitrogen-fixingmined by looking at nitrate levels and then bacteria in the soil. They will fix atmos- adding in the estimated nitrogen release (ENR) pheric nitrogen as long as the amount of freebased on organic matter levels. In reality, the nitrogen is low in the soil solution. If there isnitrogen cycle is a bit more complicated.excess nitrogen from adding synthetic nitro- Biological nitrogen is better to have as a gen, free living nitrogen fixers get the signalnitrogen source in most cases. Legumes do to go dormant and not add any more nitro- not create severe competitive stress on a cash gen to the system. crop as long as the legume growth does not In the case of mycorrhizal fungi, the plantovertake the grass. Legumes have co-evolved allows the fungi to grow inside of its rootwith grasses to grow together, sharing nutri-tissue, extending the hyphae out into theents and water via the soil biology providing soil. This increases the soil volume the plantthe grass with a nitrogen source in exchange has access to in order to obtain nutrients andfor sharing phosphate, which is required to water. In exchange for carbon from the plantfix nitrogen in the nodules. and signals of what the plant requires, theIt is quite possible to reduce the amount mycorrhizal fungi will deliver those back toof fertilizer being applied in most crop rota-the plant.tions, especially nitrogen. Using legumes as It can also link two or more mycorrhizalcash crops in rotation or including legumes as fungi-friendly plants together, sharing nutri- an intercrop or relay cover crop will generate ents and water between them. The hyphaenitrogen for the cropping system. network is present as long as it is being fed.Adding livestock grazing prior to seeding Around the hyphae are other microbes thatcrops that need a lot of nutrients is another associate with the mycorrhizal fungi. Somegood way to import nutrients if required. It increase phosphate solubility while otherscomes down to old-time agronomy to create stop nitrogen sources being degraded toa system to supply nutrients for cash crops nitrate, to name a couple of functional asso- efficiently. ciations. That means keeping costs in line so if Using cover crops will help nitrogen avail- there is a way to get nature to supply inputs ability in a couple of ways. First it will offerlike nitrogen, it will be worth looking at. 8GERMINATION.CAJANUARY 2023'