The Nitrogen Cycle
The nitrogen cycle is a natural process that describes how nitrogen moves through the environment. Nitrogen is a key element necessary for life, as it is a component of amino acids and nucleic acids, which are the building blocks of proteins and DNA.
The nitrogen cycle begins when nitrogen gas in the atmosphere is converted into a form that can be used by living organisms. This process, called nitrogen fixation, can happen through various means, including lightning strikes, certain types of bacteria, and human activities like the production of fertilizer. Once nitrogen is fixed, it can be taken up by plants and used to build proteins.
When animals eat these plants, the nitrogen is incorporated into their own tissues. When these organisms die, the nitrogen is released back into the environment through the process of decomposition. At this point, the nitrogen can either be converted back into nitrogen gas through a process called denitrification or other living organisms can take it up and continue cycling through the ecosystem.
However, it’s worth noting that “when nitrogen in its active form, such as in fertilizer, is exposed to soil, microbial reactions take place that release nitrous oxide. This gas is 300 times more potent at warming the atmosphere than carbon dioxide. It also remains active in the atmosphere for more than 100 years. Algal blooms in lakes and waterways, often caused by fertilizer run-off, also emit greenhouse gases” (Un Environment Programme, 2024).
Overall, the nitrogen cycle plays a crucial role in the functioning of ecosystems and is essential for the growth and survival of living organisms.
https://youtu.be/A8qTRBc8Bws
Video credit: Understanding Our Soil: The Nitrogen Cycle, Fixers, and Fertilizer, CC BY (Sol, 2021)
The Nitrogen Cycle: Sustainable Landscape Maintenance Practices
So, how can we incorporate the principles of the nitrogen cycle into the maintenance practices we use for restorative and regenerative landscaping?
- Reduce or eliminate fertilizer use: overuse of nitrogen-rich fertilizers can lead to excess nitrogen in the soil and runoff, which can contribute to water pollution. By using fertilizers in moderation and choosing slow-release or organic fertilizers, landscape horticulturalists can reduce the amount of excess nitrogen in the environment. Or better yet, landscape horticulturalists can look to build healthy soils to eliminate the need for synthetic fertilizer additives.
- Use nitrogen-fixing plants: some plants, such as legumes, have the ability to fix nitrogen from the atmosphere through symbiotic relationships with bacteria. By incorporating nitrogen-fixing plants into landscapes, horticulturalists can reduce the need for fertilizers and improve soil health.
- Use compost: composting organic matter can help to improve soil health and nutrient content, including nitrogen. By incorporating compost into landscapes, horticulturalists can reduce the need for fertilizers and promote healthy plant growth.
- Plant cover crops: cover crops, such as clover or rye, can be planted during fallow periods to protect the soil and improve its nutrient content, including nitrogen. Cover crops can also reduce soil erosion and improve water retention. Equally important, ensure that all loose materials are covered with a tarp or plastic when not in use to avoid leaching or washing away materials into stormwater drainage systems.
- Properly manage irrigation: overwatering can lead to waterlogging, which can reduce oxygen levels in the soil and limit the availability of nitrogen to plants.
Ultimately, we can promote healthy nitrogen cycles, soil, and plants, as well as contribute to greener and more sustainable landscape management by implementing these practices as part of a reciprocal relationship with the environment.
The Carbon Cycle
Keywords: carbon cycle, carbon sequestration, photosynthesis
As landscape professionals, we have a unique opportunity to promote green practices in our work and protect the environments we contribute to and disrupt. By implementing green practices in our work, we can reduce our environmental impact and create healthy, beautiful spaces for our communities to enjoy.
One key aspect of regenerative landscaping is understanding the carbon cycle and its importance in the ecosystems that we work in. Carbon is a critical building block of life, and it cycles through the air, water, soil, and living organisms in a complex web of interactions. Unfortunately, human activities like fossil fuel burning and deforestation have disrupted this delicate balance, leading to increased levels of atmospheric carbon and contributing to climate change.
But, wait, haven’t we already covered the carbon cycle in Chapter 3: Plants with Benefits where we looked at the role of a forest in the carbon cycle as trees sequester carbon through the natural process of photosynthesis? The answer is yes, proving the importance of why landscape horticulturalists should thoughtfully consider landscape sites as highly interconnected ecosystems and acknowledge that they have a choice of how and when they will interact and act within the ecological community.
Here is a short video to help review the process of photosynthesis and how plants use the glucose produced in photosynthesis to perform internal functions such as cellular respiration, producing glucose and amino acids, and producing and storing starch, oils, and fats. Of course, a huge benefit of the photosynthesis process is the by-product of oxygen, which all living things need to survive.
Video credit: GCSE Biology – Photosynthesis #48, (Cognito, 2018)
So, we reviewed the process of photosynthesis,, where plants take in atmospheric carbon dioxide (C02) through their stomata combine it with water (H2O) and use light energy to produce glucose (and the constituent carbon), which is then used to power their internal functions and produces oxygen that is returned to the atmosphere. Below is the formula for photosynthesis, note that the carbon molecule becomes part of the glucose molecule that powers plant functions in the leaves, stems, flowers and roots.
Photo by (Angela, 2021).
The Carbon Cycle: Soil
Overall, plants play a crucial role in the global carbon cycle by removing carbon dioxide from the atmosphere, storing it in their tissues and transferring carbon into the soil. This helps to mitigate the effects of climate change by reducing the amount of carbon dioxide in the atmosphere. Let’s explore the topic of carbon storage in the soil.
We encourage you to start by listening to Alie Ward’s Ologies Podcast https://www.alieward.com/ologies called Indigenous Pedology (SOIL SCIENCE) with Dr. Lydia Jennings.
“Soil! Dirt! Earth. Dr. Lydia Jennings, aka Native Soil Nerd, breaks down the stuff under our feet and explains everything from mining to why soil can be different colors. Also: medicine from microbes, giving back to the land after extractive processes, collecting samples in urban rivers, elders’ ecological knowledge, planting hot Cheetos, potting soil mysteries, lung fungus, the smell of rain and why gardening makes you happy. Oh and running hundreds of miles for your science” (Alie Ward, 2022).
Soil organic carbon (SOC) is the carbon that is stored in the soil in the form of organic matter. This organic matter is derived from the decomposition of plant and animal residues, as well as from the activity of soil microorganisms. SOC plays an important role in soil fertility and health, can promote healthy nitrogen cycles, soil, and plants, as well as contribute to greener and more sustainable landscape management by implementing these practices as part of a reciprocal relationship with the environment for plants and microorganisms.
In addition, SOC can help to improve soil structure, increase water-holding capacity, and reduce erosion. SOC levels can vary depending on several factors, including climate, vegetation type, soil type, and land management practices. For example, SOC levels are generally higher in soils that are covered with vegetation and have low disturbance from tillage or other practices. SOC is also an important component of the global carbon cycle, as it represents a large carbon sink that can help to mitigate the effects of climate change. By increasing SOC levels, landscape horticulturalists can help to sequester carbon from the atmosphere and store it in the soil, thereby reducing greenhouse gas concentrations in the atmosphere.
If improperly managed, soil health is degraded over time by the land management practices chosen. Let’s look to adjacent industries, such as agriculture, for examples of soil degradation.
Video credit: Mission: Keep soil alive! (Food and Agriculture Organization of the United Nations, 2021).
Now, let’s take a look at the positive impact that regenerative agriculture practices can have on the environment, in particular the soil ecosystems, in the next two videos.
Video credit: The Soil Story narrated by Larry Kopald (Kiss the Ground, 2015)
Video credit: What is Regenerative Agriculture? (Sol, 2021)
Regenerative agriculture aims to promote the health and resilience of the ecosystem by using practices that work with nature, rather than against it. The goals of regenerative agriculture include increasing soil fertility and biodiversity, reducing erosion and pollution, sequestering carbon, and improving the overall health of the land, animals, and people involved in the production process.
The Carbon Cycle: Sustainable Landscape Maintenance Practices
Landscape horticulturalists can borrow and adapt practices used in regenerative agriculture to build a greener more sustainable and mutually beneficial relationship between the land and its stewards—in part, that’s us! So, how can we incorporate the principles of the carbon cycle into the maintenance practices we use for restorative and regenerative landscaping to work with the natural cycles and not against them?
We have several alternative maintenance practices to choose from to improve soil organic carbon (SOC) and overall soil health. These practices aim to store carbon and promote the health of the soil and the organisms that live in it, ultimately supporting plant, animal, and human health. Here are some examples:
- Reduced tillage: tillage can disrupt soil structure and lead to the loss of organic matter. By reducing the frequency and intensity of tillage, landscape horticulturalists can help preserve SOC and maintain soil health. In other words, choose landscape construction and maintenance practices that are the least disruptive to the soil.
- Mulching: but not necessarily bark mulch. Applying organic mulch, such as compost or wood chips, to the soil surface can help to increase SOC levels by providing a source of carbon and other nutrients for soil microorganisms. Mulch can also help to regulate soil temperature and moisture, reducing the need for irrigation and improving plant health.
- Composting: composting organic wastes, such as leaves, grass clippings, and food scraps, can help to produce a nutrient-rich soil amendment that can be added to the soil to increase SOC levels and improve soil health. Or, better yet, leave the leaves! Instead of changing the aesthetic of a garden by “cleaning up” or removing leaves, flowers, or debris in a fall clean-up, consider educating the clients to help change their perception of what a healthy garden is and does for the ecosystem.
- Planting cover crops: cover crops, such as legumes, grasses, and clovers, can help to improve soil health by fixing nitrogen, reducing erosion, and adding organic matter to the soil. For example, if a landscape project is scheduled over a long period of time, consider planting a cover crop to avoid bare soils that are prone to erosion.
- Integrated Pest Management (IPM): using IPM practices, such as physical, cultural, and biological controls, can help to reduce and ideally eliminate the use of synthetic pesticides and fertilizers, which can have negative impacts on soil health and SOC levels.
- Leave the leaves: changing the way we perceive beauty in the landscape can have a significant impact on the carbon (re)entering the carbon cycle and regenerating soil carbon stores for microorganisms that break down the carbon into usable nutrients for plants to continue the cycle.
Overall, landscape horticulturalists can use a combination of these practices to improve soil health and SOC levels, which can lead to healthier plants, improved water quality, and healthier ecosystems. The nitrogen and carbon cycles and the process of photosynthesis are just a few examples from the harmonized landscape horticulture curriculum of how instructors can connect natural cycles and processes to sustainable landscape construction and maintenance practices.
To finish off this section of the chapter, we encourage you to watch the video below. The video reviews the carbon cycle but will help us transition into the next section of the chapter, alternative energy, which focuses on how technology can support landscape horticulturalists in making sustainable choices to reduce their environmental impact.
Video credit: Healthy Lawns and Landscapes Fight Climate Change, (National Association of Landscape Professionals, 2021).
Teaching and Learning Examples for Instructors
- Assignment: Connecting Natural Processes to Landscape Maintenance Practices for Sustainability Note This assignment was created by Chatgpt, you can adapt it for your region and learners as needed.
Reflect
Please use the following questions to guide your reflection:
- In what ways do you currently connect natural processes to the curriculum you teach?
- Do you think that students would be receptive to connecting natural processes to the horticulture skills and practices they choose to apply in the industry?
- How can you help guide students to communicate natural processes and their impact on the horticulture skills and practices applied to clients?
Feedback/Errata