Healthy Soils

The protection and cultivation of healthy soil is critical to the Earth’s biosphere, clean water supply, and global food availability, yet it is frequently overlooked and misunderstood. In addition to supporting plant life, healthy soil provides habitat for local species, promotes biodiversity, increases carbon sequestration and storage, increases the capture of water into underground aquifers, improves water quality in the watershed, and reduces (and often eliminates) the need for fertilizers and pesticides.

Healthy soil is a fundamental aspect of Surfrider Foundation’s Ocean Friendly Gardens program, which takes a watershed approach to increase recreational water quality at the beach.

Soil is More than Just Dirt
Often times people use the words dirt and soil interchangeably, when really, soil is so much more:

"'Dirt' describes the physical qualities of the rock particles and cannot be changed by gardeners. 'Soil' describes the complex living collection of dirt, organic matter, billions of microorganisms, plants, bugs and chemistry that hold it all together. Healthy, living soil is a sponge for water, an immune system and restaurant for plants, and a storage box for carbon. Healthy soil is alive, and gardeners can create living soil.” – Green Garden's Group Sustainable Landscape Guidelines

Microbes and Soil Critters
Microbes are microorganisms, like bacteria, fungi and protozoa, and are essential components of healthy soil. Microbes decompose dead plants and animals, manure, and pesticides; protect water quality; increase the ability of soil to retain water; and make critical nutrients bioavailable to living plants and animals. This is especially important when it comes to nitrogen fixing-bacteria. Nitrogen is a nutrient required for plant growth but frequently limited in soil. Some microbes even have a symbiotic relationship with plants where they inhabit plant roots and feed on the root’s sugars and carbon, and in return, the microbe (in this case, rhizobia) provide nitrogen to the plant. Certain fungi have similar symbiotic relationships, where they infect and feed off of the plant roots but in return, help the plant better absorb water and nutrients. Learn more about symbiotic microbe-plant relationships from Sustainable Agriculture Research and Education.

In addition to supporting plant life, microbes are also a primary producer in the food chain, providing the basic nutrition for invertebrates like worms (nematodes) and beetles (arthropods). These animals further help decompose organic matter and add nutrients to the soil, while also providing a food source for larger animals like birds and mammals. Learn more about the Soil Food Web from USDA’s Natural Resource Conservation Service.

As mentioned, microbes feed on organic matter (like roots, twigs, and leaves) but they also need water and oxygen to survive. Fortunately, microbes and other soil critters like earthworms and centipedes help create air pockets in the soil, providing room for oxygen. If there is no oxygen, the soil becomes anaerobic and can promote “bad bacteria” that result in plant diseases. This can happen from soil compaction and/or over watering.

“Life in the soil includes all of the bacteria, protozoa, nematodes and fungi, the food they eat, the excretions they make, and the root systems they sustain. Living microbes most quickly can be incorporated into soil by adding really good quality compost. Plants attract microbes to their roots by feeding them carbon. Bacteria and fungi hold the soil together with microscopic glues and binders. The microbes consume organic matter and are then consumed themselves by larger creatures (worms, ants, slugs, centipedes, insect larvae, etc.) In turn, these creatures are consumed by creatures further up the food chain. Carbon and other nutrients are cycled through these many life forms, creating healthy, living, well-structured soil, no matter what the soil type.” – Green Garden's Group Sustainable Landscape Guidelines

Permeability and Water Retention
Permeability is the ability of water or liquid to percolate through a substance. For instance, a concrete road has extremely low permeability, because the concrete is tightly bound together and blocks water from getting through. Alternatively, a garden with healthy soil has higher permeability, because the water can fit and move between soil particles. This is why “impermeable surfaces” like concrete roads, sidewalks, and channeled streams increase the amount of polluted runoff that reaches the coastline. Instead of percolating through healthy soil, getting processed and cleaned by microbes while it slowly makes its way to the nearest water body, polluted runoff quickly flows down impermeable surfaces, funneling straight into water bodies without any filtration.

In general, the smaller the particle, the less the permeability. So though almost all soil is more permeable than concrete, soil type can impact the level of permeability, with smaller fine clay generally being less permeable than larger coarse sand. This also highlights the importance of reducing soil compaction, as too much compaction forces particles closer together, blocking air pockets, preventing water percolation and reducing soil oxygen content.

Relatedly, water retention is the ability of a substance to hold water, with larger particles having less water retention. For instance, a sandy beach generally has low water retention because the sediment is so permeable. Water infiltrates a sandy substance and then percolates right through. Fine clay, however, has higher water retention. Once water gets in, it is unable to move as freely through the sediment (low permeability) so water is better held in place. In this way, medium to fine soil types act as sponges, absorbing and holding water. The process of holding water is due to a more technical mechanism known as capillary action. Dive deeper into the physics of water retention from the Plant and Soil Sciences eLibrary, a resource provided by the USDA, National Science Foundation, and UC Davis.

The best sediment for gardening and crop agriculture is one that balances water permeability and retention, which is generally found with loam (equal parts sand, silt, and clay). This mix provides a balance where water is able to infiltrate into the soil but not move too quickly through it. The water is held between the soil particles, and becomes “available soil water” to plant roots. If too much water is applied and held, the soil can become saturated, meaning all air pockets fill with water, and the system becomes anaerobic. Not only do anaerobic environments suffocate the “good” microbes, but they also create an environment where certain disease causing anaerobic bacteria can flourish and harm plants and root systems. Alternatively, if there is not enough water in the soil, plant roots are unable to access water, the “permanent wilting point” is met, and plants will not survive.

Carbon Sequestration and Storage
Plants provide a natural method of removing carbon from the atmosphere through photosynthesis, and then storing or “fixing” much of that carbon in their tissue, roots and soil. This process is known as carbon sequestration. Over time, when the plant dies or gets consumed by animals and returned to the soil as litter, it helps create soil organic matter (SOM), also known as compost, which is extremely nutrient rich and loaded with fixed carbon. Healthy soils mean stronger carbon reservoirs and healthier plants, which will continue to take carbon out of the atmosphere, build SOM, and promote growth of new plants, providing a feedback loop that could help bring the system back into balance.

Approximately 75% of the terrestrial carbon is actually in the soil, and in its healthy state can store up to 11 gigatons of CO2 every year. Some estimate that "soil sequesters four times more CO2 than all the world’s plants including forests". However, when we lose healthy soils by developing over natural areas, or by conducting conventional agricultural practices like clearcutting, tilling, and over-grazing; we reduce the ability to use this reserve as a natural storage of carbon. We also release the carbon that’s previously been captured back into the atmosphere. To prevent the severe impacts from exacerbated climate change, we can’t just rely on healthy soils to offset our impact. We need to stop adding additional carbon into the atmosphere as soon as possible, but to help alleviate the damage we’ve already done to our planet, and to sequester some of the carbon that we’ve already added to the atmosphere, we need to cultivate and protect healthy soils. Learn more about soil carbon sequestration and storage here.

The Benefits of Compost and Mulch
Compost helps kick start the transition from dirt to healthy soil, providing water, oxygen, and essential microbes. Once the plants grow, their own leaf litter and root systems can act as self-made mulch and compost. Compost itself is pre-decomposed organic matter through the use of carefully selected and fed microorganisms and worms. Check out this EPA website to learn more about composting. While compost is added and mixed within the soil itself, mulch is more of a topping, placed over the soil to help maintain soil moisture, prevent weed growth, and mitigate effects of temperature change on root systems. It is recommended to use organic materials for mulch, like untreated wood chips and leaf litter, as they will decompose overtime and add nutrients back into the soil.

Risk of Conventional Agriculture & Landscaping
Fertilizers
Conventional crop agriculture relies on soil additives instead of investing the time and effort into nourishing naturally nutrient rich soils. To get the nutrients needed for successful plant growth, nitrogen and phosphorus rich fertilizers are added to the soil. Because fertilizers are generally affordable, they are frequently over-applied, resulting in runoff with high concentrations of nitrogen and phosphorus. If this nutrient rich runoff reaches water bodies without being filtered through healthy soil (for example, is directed to a storm drain or channelized river heading straight to the coastline) the excess nutrients cause “eutrophication” and algal growth. These algae blooms can result in “dead zones”, or areas of water with no dissolved oxygen that are unable to sustain aquatic life. Learn more about the process of eutrophication, and the causes and effects of algal blooms from the Beachapedia article on Cyanobacteria and red tides. Recent studies have also found that fertilizers introduce salts into the environment, causing freshwater environments to become saltier, a phenomenon known as "Freshwater Salinization Syndrome". This "syndrome" changes important ecological parameters, including the pH, and releases toxic metals and harmful nitrogen compounds from streambeds and soils. In addition to becoming an aquatic pollutant, nitrogen rich fertilizers can also contribute to atmospheric pollution (releasing nitrous oxide) and soil acidification. To help prevent the over-use of nitrogen rich fertilizers, scientists are actively trying to develop affordable, rapid soil testing methods for farmers to use when determining compost or fertilizer needs.

Non-native Plants and Invasive Species
Conventional agriculture and landscaping generally use exotic, non-native plants. This is especially common for fruit and vegetable crops, as well as ornamental greenery. For instance, soy beans are native to East Asia, yet they are grown all over the Midwest of the United States. Because soybean plants developed to thrive with the conditions, pests, nutrients, and climate of East Asia, soybeans require a lot of habitat manipulation to successfully grow in the Midwestern United States. This includes irrigation to make up for different soil types and climate, application of pesticides to prevent damage or competition from Midwestern bugs, plants, and critters that they naturally wouldn’t be exposed to, and addition of fertilizers to make up for the difference in soil nutrient levels. To note, fertilizers are also used to increase a crop’s production, be it quantity or size of fruit/vegetable.

Exotic plants can also risk the natural environment beyond a specific farm or yard, by introducing a non-native plant or animal species to the ecosystem. As mentioned, non-native or invasive species have adapted to their native environment over generations, yet when they are translocated or planted in another environment, their reaction can vary. Sometimes they require the help of water and additives to survive, other times, they are actually able to outcompete native plants or animals, causing potentially severe impacts and alterations to an entire ecosystem.

Pesticides & Herbicides
By their very nature, pesticides and herbicides are toxic, as they are meant to kill unwanted plants and animals. However, there are certain herbicides that are not toxic to mammals (including humans), so be sure to read the ingredients carefully. Unfortunately, like fertilizers, pesticides and herbicides rarely stay where they are applied, and can enter the watershed and environment through runoff and airborne transport. Even when applied carefully, certain pesticides are able to penetrate the skin of various fruits and vegetables, exposing humans and wildlife to toxic consumption, even after rinsing. Check the Environment Working Group’s annual list of Dirty Dozen to see which fruit and vegetables tested highest for lasting pesticide residue. Pesticide consumption and exposure has been linked a wide-variety of human and wildlife health issues.

Grass Lawns, Monoculture, and Artificial Turf
Conventional landscaping, such as grass lawns, are highly water intensive, and do little to provide habitat for native wildlife. The use of a single plant species also reduces the biodiversity and native habitat of the landscape, and results in increased reliance on pesticides to prevent invasive weed growth. Artificial turf is frequently used in place of grass lawns to reduce water reliance, but unfortunately artificial turf installers encourage soil compaction, which reduces oxygen content and can kill those essential soil microbes and critters. There have also been concerns about human and environmental health impacts from the leaching of chemicals from artificial turf. The best way to protect local environment and wildlife when landscaping or farming - is to promote healthy soils and use native vegetation as much as possible.

Techniques and Methods to “Garden with Nature”
Learn how to promote healthy soils and grow ocean friendly gardens with Surfrider Foundation’s Ocean Friendly Gardens Guidebook and website. Be sure to check out the resources tab for even more how-to's and information on gardening with nature. The Green Gardens Group also has some great step-by-step instructions for a watershed approach to landscaping in various regions. You can also start incrementally, for instance by building your own home composting system! Great guides include Your Guide to Building a Worm Composting Binand Composting 101.

Regional Resources
To garden with nature, you need to use local plants adapted to your respective region and climate type, soil types, and seasonal influence. See below for some regional resources to help you source the right plants and soil types for your Ocean Friendly Garden. Pacific Northwest

• City of Portland Oregon's Gardening Resources
• Oregon Metro's Tools for Living: Plants
• Washington Toxic Free Future's Lawn and Garden Care

California

• Watersmart San Diego’s Sustainable Landscape Design
• Greg Rubin & Lucy Warren's book The California Native Landscape
• Green Garden’s Group California Watershed Approach to Landscape Design

Mountain West

• University of Nevada's Combustibility of Landscape Mulches
• Learn to Grow's Water Wise Gardening: Mountain West and High Plains

Southwest

• Austin Real Estate's Homeowners Guide to Composting

Midwest

• Michigan Dept of Environmental Quality’s Mulching and Backyard Composting Guidebook
• University of Minnesota’s Composting and Mulching: a Guide to Managing Organic Yard Wastes

Northeast

• Maine Dept of Environmental Protection’s Guide to Recovering and Composting Organics in Maine
• Lee Miller’s A Guide to Northeastern Gardening

Southeast

• Clemson University's Home and Garden Information Center

Hawaii

• University of Hawaii's Native Plants Hawaii

Additional Information on Soil Carbon Storage

• Todd Ontl & Lisa A. Schulte's Soil Carbon Storage

References