Green Roof plants, as well as every other living organism on the face of the earth must take this nitrogen and build protein, amino acids, nucleic acids, DNA and other life-giving substances.
|Green Roof Legumes companion planted|
However most of the atmospheric nitrogen exists in a form that cannot be used unless converted into ammonia. Ammonia is formed from one nitrogen and four hydrogen atoms. Ammonia is the substance living organisms use to process nitrogen into life.
On a rooftop or in a garden, available ammonia nitrogen amounts are usually discernible by shades of green across leaves. Darker green typically represents strong availability of ammonia nitrogen whereas light green or yellow leaves may indicate a serious lack of available ammonia nitrogen.
One school of thought concerning ammonia nitrogen availability focuses on use of industrially processed ammonia compounds in the form of liquid or more commonly, pelletized fertilizers. However with the world's waterbodies, lakes, rivers and springs quickly eutrophying with runoff carrying excess ammonia and phosphorous, industrial fertilizers are coming under frequent criticism.
Adding industrial fertilizers to green roofs may compound existing pollution problems.
Another perspective for providing green roof with adequate supplies of ammonia fertilizers is an approach incorporating nitrogen fixing plants into green roof plantings.
Nitrogen fixing plants are commonly represented by the well-know legume families such as clover, beans and other 'green manure' plants where the nitrogen in the form of nitrogen gas, N2, is converted to ammonia, NH4, by bacterial processes. The NH4 is then released to the soil and plants when either the bacteria die or the bacteria live in close association with plants.
Planting nitrogen fixing plants on a green roof can reduce or eliminate all together the necessity of additional industrial fertilizers.
The opportunity to use nitrogen fixing plants to provide ammonia really caught my attention over the last year as we worked with floating wetland technology.
Hoping floating wetland plants would clean stormwater through uptake of nutrients, the research conducted ultimately pointed towards a very interesting conclusion with green roof fertilizer implications.
In waterbodies with low nitrogen concentrations (very clean lakes, streams and rivers) the water under and around the floating wetlands had higher than normal nitrogen concentrations.
At first these findings were a big surprise yet as we looked at the systems from a more global perspective and noticed the presence of certain nitrogen fixing plant and bacteria species the results began to make sense.
Nature knows when ammonia fertilizers are needed and provides the biological process to accomplish such.
In a time of severe water pollution and excess nutrients we should be looking to nitrogen fixing plants for green roof fertilizers.
Especially in Urban Core areas where NOx and SOx smog is bad, plants not only make fertilizers available but clean the air in the process.
Many of the plants in the Fabaceae family fix nitrogen. Wikipedia offers some interesting perspectives on the topic also.
Studies have shown nitrogen fixing plants can add up to seventy five pounds of nitrogen to the soil per acre in natural ecosystems and up to several hundred pounds per acre in cropping systems.
Nature can teach us (biomimicry) about important agricultural and green roof considerations. There are many web resources available for more information on nitrogen fixing plant types and their biological processes.
Next time you consider applying industrial fertilizers, try using nitrogen fixing plants . You'll be helping keep our waterbodies free from algae blooms, cleaning the air, providing your plants with needed nitrogen and much more.