All life requires nutrients such as nitrogen, phosphorus, and potassium to manufacture cellular components and regulate metabolism. Plants are the base of food chains not only because they produces energy from photosynthesis (organic carbon), but also because they transform inorganic nutrients such as nitrogen into labile organic forms.
Inorganic fertilizers are problematic for several reasons. First, inorganic fertilizers imbalance and destabilize the ecosystem by enriching it with an unusual level of nutrients that move through the system unnaturally due to their inorganic chemical form. Second, inorganic fertilizer production consumes fossil fuels and represents a contributing factor to consumption and climate change. Third, the use of inorganic nutrients leads to the respiration of soil carbon and other organic soil nutrients. As a result soils lose their water and nutrient holding capacities necessitating greater future soil amendments. Finally, applied inorganic nutrients frequently leave the system they were applied and create pollution in another.
Nitrogen is the primary nutrient of concern for most farmers in Illinois To meet their demands most farmers use anhydrous ammonia or urea. These forms of nitrogen are produced from fossil fuels and quite mobile and thus leach quickly out of the system into runoff or groundwater. The problem of nitrogen and nutrient leaching is compounded by the practices of annual crop cultivation; a lack of soil carbon and tillage, which remove any natural buffers the system might have to pollution (e.g. inorganic fertilizers). Nitrogen is thus a common environmental pollutant especially in areas that cultivate large areas of annuals such as the Illinois.
To deal with the problem of nitrogen at PrairieGreens we utilize a perennial polyculture of legumes and forage grass. All species sequester carbon which serves to increase nitrogen retention. The plant’s roots also absorb any labile nutrients in the system and minimize runoff and groundwater pollution. Legume species in our polycultures feed carbohydrates from photosynthesis to symbiotic bacteria living in their roots. In exchange for the energy and a place to live, the bacteria give some of the nitrogen they produce enzymatically to their plant host. As legumes decompose their organic matter serves as a nitrogen source for the system. We harvest or cut our crops on occasion to encourage growth, but return to the system what is harvested as green manure.
Managing nitrogen in this manner demands we dedicate a sizable portion of our farm to perennial polycultures rather than crops; however, this land is not unproductive. In addition to producing nitrogen these polycultures produce flowers that serve as forage for bees and serve as habitat for predatory insects. In a pinch these polycultures can be harvested as a nutritious hay loaded with minerals and just the right amount of protein (this will vary with species composition, but ours is designed for this purpose). Our polycultures are also loaded with medicinal and culinary herbs, cut flowers, fiber plants, etc.; all of these can be harvested during periods of nitrogen production. Finally, perennial polycultures discourage or disrupt pest and disease outbreaks and are a great overall cover crop.
While there are ample amounts of phosphorus present in our soils they are slowly released. Levels in the soil are generally ample for the growth of most crops since very little is removed from the system. When we need to concentrate the phosphorus found in plant matter we use often use the same methods of composting and green manure as is used for nitrogen. When we need an even greater nutrient boost we can apply our composted alpaca manure.
We are lucky to have soils rich in potassium and don’t need to modify levels. However, if we do need to provide potassium in the future we would use ashes from invasives we clear and burn.