b'COVER CROP CORNERWhy Cover Crops are One of Natures Nitrogen SourcesWITH THE PRICE of synthetic nitrogen taking offthe vegetative stage is also a positive option, tying up in price the last couple years, profitability has beenfree nutrients and releasing root exudates to stimulate challenged. Nitrogen is one of the largest expenses onsoil biology and creating good soil structure. Including most farms and plants respond quickly to additionslegumes in the mix will ensure there are plants with and deficiencies in the field. Yet in areas that we arentnitrogen-fixing relationships with rhizobium. This is farming, plants seem to be growing and thriving withoutimportant as the legume nitrogen fixation tends to be additions of synthetic fertilizer. Whats happening? greater in an agricultural system than the free-living In native plant stands, being either grass-based ormicrobes by themselves. treed, plant growth seems to be adequate to cover theThe reason synthetic nitrogen is used over biological KEVIN ELMY,ground and produce aboveground biomass. Wherenitrogen is predictability. Sir Albert Howard saw this is founder of Coverdo these nutrients come from? Nature has evolvedback in the early 1900s; farmers wanted the easy button Crops Canada. His book Coverover centuries to have an elaborate system of plantseven though synthetic nitrogen applications turn out to Cropping incapturing sunlight through photosynthesis creatingbe only 50 per cent effective in most cases. Biological Western Canada is available throughsugars that the plant can use for plant growth and asnitrogen production will be dependent on weather, Friesen Press,exudates to feed microbes on the leaves, stems andsoil type, plant density, other species growing, proper Amazon, and digitally throughroots. The exudates released through the roots feedinoculation with the correct rhizobium, and soil Apple Books,soil microbes that will in turn free up soil-boundmicrobial activity including mycorrhizal fungi. Kindle, and Google Play. For morenutrients for the plants.But because agronomists are trained with traditional info on CoverThis isnt a random set of events; the plants knowsoil tests, nitrogen supply is determined by looking at Crops Canada visit covercrops.ca who in the soil can get certain nutrients that the plantnitrate levels and then adding in the estimated nitrogen requires so will signal those microbes by modifyingrelease (ENR) based on organic matter levels. In reality, the root exudates to attract the microbes that can makethe nitrogen cycle is a bit more complicated.those nutrients available. Even though there may notAnother topic that science has oversimplified be a significant amount of legumes in the stand, plantsis nutrient uptake by plants. Biological nitrogen is arent nitrogen deficient.better to have as a nitrogen source in most cases. There are free living nitrogen-fixing bacteria in theLegumes dont create severe competitive stress on soil. Theyll fix atmospheric nitrogen if the amount ofa cash crop if the legume growth doesnt overtake free nitrogen is low in the soil solution. If theres excessthe grass. Legumes have co-evolved with grasses to nitrogen from adding synthetic nitrogen, free livinggrow together, sharing nutrients and water via the soil nitrogen fixers get the signal to go dormant and not addbiology providing the grass with a nitrogen source in any more nitrogen to the system. exchange for sharing phosphate, which is required to In the case of mycorrhizal fungi, the plant allows thefix nitrogen in the nodules. fungi to grow inside of its root tissue, extending theIts quite possible to reduce the amount of fertilizer hyphae out into the soil. This increases the soil volumebeing applied in most crop rotations, especially the plant has access to in order to obtain nutrientsnitrogen. Using legumes as cash crops in rotation and water. In exchange for carbon from the plant andor including legumes as an intercrop or relay cover signals of what the plant requires, the mycorrhizalcrop will generate nitrogen for the cropping system. fungi will deliver those back to the plant.The amount of nitrogen generated for the cash crop It can also link two or more mycorrhizal fungi- will vary due to many influences, including the plant friendly plants together, sharing nutrients and waterdensity and nitrogen requirements. between them. The hyphae network is present if itsAdding livestock grazing prior to seeding crops being fed. Around the hyphae are other microbes thatthat need a lot of nutrients is another good way to associate with the mycorrhizal fungi. Some increaseimport nutrients if required. It comes down to old-phosphate solubility while others stop nitrogentime agronomy to create a system to supply nutrients sources being degraded to nitrate, to name a couple offor cash crops efficiently. Net dollars are the goal one functional associations. should be aiming for. Using cover crops will help nitrogen availability inThat means keeping costs in line so if theres a way a couple of ways. First, itll offer hosts for mycorrhizalto get nature to supply inputs like nitrogen, itll be fungi, which is always a good thing. A living plant inworth looking at. 50SPUDSMART.COM Winter 2023'