The Difference Between Fertilizer And Compost

By Graham Towerton

At Food Forest Abundance we’ve been hosting strategy sessions all over the world with hundreds of people. If you are reading this and you haven’t booked a strategy session yet, get yourself to our home page to book one as soon as you’ve read this article!

A common question that we get in these sessions is “what do I do to fix my soil?” There are endless types of soil depending on sand, clay, and loam content; how much organic matter is present, the soil moisture content, and its mineral nutrient content. People who are practicing permaculture or other sustainable agriculture methods are always wanting to avoid the use of synthetic chemicals, whether for fertilizer or for pest and weed control. Is there a way to manage soil fertility without the use of chemical fertilizers? The answer is most definitely “yes”.

Chemical Fertilizers

So what are chemical fertilizers? As all nutrients used by plants can be classified as “chemicals” of some form, I prefer to use the term “synthetic fertilizers” to describe those fertilizers which have been manufactured to form a compound that might not be found in nature. 

The main elements needed by plants include nitrogen, phosphorus, and potassium. Often you will see these listed on fertilizers as N, P, and K (their elemental chemical symbols). Conventional agriculture considers calcium, magnesium, and sulfur also to be essential macro-nutrients and then considers boron, copper, iron, manganese, zinc, chlorine, cobalt, silica, and molybdenum to be “trace” or micro-nutrients. Rarely does conventional agriculture consider the necessity for plants to use any of the 70 or more additional elements found in nature.

Instead of considering soil as a habitat in which plants, fungi, bacteria, insects, worms, and many other creatures can exist together, conventional agriculture considers soil simply to be a sterile growing medium into which soluble plant nutrients are added to stimulate and control the growth of plants. Whether the “crop” is corn, soybeans, or the typical residential lawn, the approach is generally the same i.e. ignore the soil flora and fauna and feed the plant with chemical fertilizers.

Let’s discuss some common synthetic fertilizers.

Nitrogen fertilizers typically come in the form of ammonia, nitrate, and urea-based compounds. Ammonium nitrate and urea are the two main forms of nitrogen fertilizers used in commercial agriculture and both of these are synthetic chemicals made from other chemicals. Ammonium nitrate is made by reacting nitric acid and ammonium hydroxide and both of these chemicals are also manufactured or synthetic. Urea is made by reacting ammonia with carbon dioxide and ultimately comes from natural gas for the production of these ingredients.

Common phosphorus-based fertilizers include phosphoric acid and monocalcium phosphate (or “super” phosphate). The latter is produced by reacting sulfuric acid with rock phosphate. Essentially all phosphorus-based fertilizers come from this chemical digestion of phosphate rock, followed by other reactions to purify and modify the chemical. Most phosphate fertilizers formed in this way can contain impurities from other elements including zinc and other heavy metals, as well as fluoride and aluminum.

The most common form of potassium fertilizer is potassium chloride which is generally obtained from potassium salt deposits. Other forms of potassium fertilizer include potassium sulfate and potassium nitrate.

One thing that all of these chemicals have in common is a high level of water solubility. Quite commonly in commercial agriculture, these chemicals are applied in irrigation water, or by “drilling” the liquid fertilizer into the soil at the time of planting. Fertilizers for home and garden use are usually pelletized solids but are also generally water-soluble. By having all of these chemicals water soluble, the theory is that they are readily available for uptake by the roots of the plants, resulting in faster growth. While the faster uptake and growth are true, there are numerous problems created in soils by the use of these fertilizers.

Harmful Effects of Chemical Fertilizers

The water solubility of these chemicals which is described as a benefit for plants is also a detriment for many other reasons. With heavy rainfall or excessive irrigation, the water-soluble chemicals can leach right through the root zone of the plant making them unavailable for use and entering the groundwater table where the chemicals become a pollutant. Water soluble chemicals can also wash easily from the soil into rivers, streams, and lakes causing algal blooms and depletion of oxygen leading to fish kills and death to other aquatic species.

While phosphorus is soluble in the form of liquid fertilizers, as soon as it hits the soil it starts to react with calcium and other soil minerals and more than 70% of the phosphorus becomes insoluble and immobile in the soil. 

In order to make commercial farming more cost-effective, chemical fertilizers are generally supplied in high concentrations and misapplication of these can burn plants. Even with the correct application methods, fertilizers can kill all of the soil micro-organisms.

It is this death of the soil micro-organisms that are the most harmful effect of all. An understanding of how plants interact with the soil and its micro-organisms is important in order to realize this fact.

In the diagram above, several relationships are shown between soil microbes and fungi, and plants. In a natural environment, bacteria and fungi receive their nutrition from the roots of plants while also providing plants with the nutrients it needs. Some soil microbes are responsible for breaking down soil minerals into soluble forms, while plant roots release organic acids that also dissolve minerals for uptake in the roots. Yet other microbes extract nitrogen from the air and convert it to ammonium and nitrates for plant roots to uptake.

So what happens when chemical fertilizers are applied?

• The local pH (acidity/alkalinity) can be altered causing certain minerals to become insoluble and killing any microbes that cannot tolerate the change in pH
• If an ammonium fertilizer is applied in high concentration, then all other nitrogen-converting bacteria will disappear from the soil
• The plants become 100% dependent on the chemical fertilizers and unable to process naturally present minerals and nutrients
• Unless the farmer/grower provides a complete fertilizer program with ALL the mineral and nutrient needs of the plant, the plant will be deficient for those leading to plant stress and susceptibility to pests and disease
• There is an almost total destruction of the organic matter within the soil, which will be discussed as part of the next sections on compost and organic materials.

Compost and Organic Materials

Compost is simply decomposed organic materials. What organic materials can be part of compost? Essentially, anything that was once part of anything living. 

The approach with chemical fertilizers is to feed the plant with water-soluble nutrients and minerals. The approach with compost and organic materials is to feed the soil and all of its inhabitants, with the belief that natural processes will ensure the nutrients and minerals are available for the plant.

Consider a redwood tree in a forest in the Pacific Northwest of the USA, or a eucalyptus tree in the forests of Australia. These trees can become massive and grow hundreds of feet in height. Where did their nutrition come from? It certainly didn’t come from people applying chemical fertilizers. Look through the forests of the world and you will find the same story - a layer of organic material covering the soil, a process of decomposition of the fallen leaves, branches, and trees, and a rich environment of organisms within the soil itself.

Within the decomposing organic material, there is a rich source of nutrients and minerals, all readily usable by other plants, or by the soil microbes. There are small amounts of “manure” being the droppings of forest animals and other nutrients supplied by the decomposition of dead insects and animals. Within diverse forests there are many diverse plants that have different functions, some are nitrogen fixers, some have deep taproots to access deeper nutrients to bring to the surface and store in their leaves, and others act as hosts for specific soil inhabitants that benefit the overall soil health, some have large volumes of fibrous roots to open up the soil. When all of these plants die, their decomposition provides the surface soil layers with new minerals and nutrients and other important organic substances.

One of these is humic acid. Quite often the term “humus” is used to describe the very rich brown/black compost-like material that can be found in the bottom layers of leaf litter in a forest; or in very well-developed man-made compost. “Humates” is another term used to describe mined materials that are formed from organic materials from eons ago that were then covered with other layers of soil and rock. Both humus and humates are rich in humic acid which is one of the more important organic compounds in soil. Humic acid plays a role in the exchange of water-soluble minerals between the base rock and the plants. Whether the base rock is dissolved by microbes or organic acids released by plant roots, humic acid acts as a “sponge” for these dissolved minerals, absorbing them when formed, transporting the minerals, and releasing them when needed by plants.

Soil that is devoid of organic material has a very limited capacity for this mineral exchange and a limited ability to retain moisture.

Another very important aspect of an organic soil fertility program is the formation of mycorrhizal fungi which also play a major role in the absorption, transportation, and release of minerals and nutrients for plants. These fungi generally only populate the soil when it is rich in organic matter and is not heavily contaminated with chemical fertilizers. These fungi send out very tiny filaments through the soil and one literature source suggests that up to 195,000 miles of these filaments may exist in an acre of topsoil, all interconnected and sharing nutrients.

Tilling the soil breaks up this network, so a no-till gardening method is encouraged. Adding chemical fertilizers, especially phosphorus, can be detrimental as plants will absorb this source instead of making use of the “trading” relationship with fungi and will then miss out on all of the other minerals needed. Pesticide use also causes damage to these fungi.

The mycorrhizal fungi relationship with plants does not only provide an exchange of nutrients, but the fungi also help to control other soil-borne pests and diseases. These fungi have been demonstrated as an effective control for root-knot nematodes, literally mobilizing, killing, and consuming nematodes.

Scanning electron microscopy of the carnivorous fungus Arthrobotrys anchonia capturing a nematode. 

Attrribution: George Barron, University of Guelph, Canada, Creative Commons

What Makes Good Compost?

Any organic material may be used for compost. Kitchen scraps, lawn clippings (with no chemicals), leaves, twigs, and branches from tree prunings, dead plants, straw, and spoiled hay (also untreated with chemicals)  all may be considered for use in making compost.

There are many methods for making compost that can be readily found on the internet that can be used depending on the scale of compost production you want to achieve.

Me, my two favorite materials are wood chips and leaves. I collect leaves from the local neighborhood in the fall and will lay these on top of the soil with a depth of 18-24” over any area of soil or lawn that I am wanting to reclaim for new organic gardens. I receive wood chip deliveries from the local tree service contractor delivered for free, as I am saving them the travel distance and tipping fees at the local landfill. Wood chips I lay over the soil or lawn at a depth of 8-12”. I choose these two materials because they are free are rich in minerals and plant nutrients and generally free of pesticides.

Both of these methods are effective for my purpose of killing the lawn grasses, preventing the soil from freezing hard through winter, and allowing the soil critters to do their job by incorporating the organic materials into the soil. Even in February, I am able to part the leaves or wood chips to reveal earthworms working at the soil surface.

My chickens also perform a valuable role in this activity, turning over the leaves and wood chips in their hunt for insects, grubs, and seeds; also manuring the leaves and wood chips at the same time.

Leaves laid over the grass at 18-24” depth. Photo by author.

After the leaves and wood chips are removed from the soil in spring, I will pile these up to start the true composting. It is amazing though to see how much decomposition occurs even in winter. Quite often I will find fungal growth in the wood chips and leaves. After piling it up, I let the chickens work for the piles.

Piles of wood chips and leaves in various stages of composting. Photo by author.

After these materials are fully composted I use them in a number of ways. Composted wood chips are placed in the bottom of raised bed gardens acting as a reservoir for soil moisture and plant nutrients for easy access by the roots of whatever plants are grown in the beds.

Composted leaves are applied as the next layer in raised bed gardens and sometimes mixed with soil to create the planting medium in the raised beds. I also use leaf compost to replenish my garden beds every 2-3 years.

Freshly placed leaf compost before transplanting strawberries. Photo by author.

It’s important to note that by using these practices it’s entirely possible to avoid the use of synthetic fertilizers and chemical pesticides and herbicides. We have lived on our property for 8 years and the only fertilizer I have not applied is any synthetic fertilizers, pesticides, or herbicides - only compost.

Because of the high level of organic material in and on my soil, I also have less work to do for watering my gardens. I do not have an irrigation system established at all and I rely primarily on rainfall to provide all the water for my plants. The heavy mulching and composting ensure the water stays close to the root zone instead of percolating straight through my sandy/gravelly soil. Occasionally we will have a dry spell of 2-4 weeks in mid-summer, but the only plants I will water in those dry spells will be my smaller annual crops and any newly planted seedlings or trees, using rainwater from my collection tanks. 

Abundance is possible without the need for chemical fertilizers, pesticides, or herbicides!

Graham Towerton is a retired chemical engineer with 34 years of experience working in various chemical manufacturing industries including oil refining, petrochemicals, oil & gas production, mining, and biofuels industries. He has also formulated over a hundred liquid chemical fertilizer products for use with crops in west Texas and California’s San Joaquin Valley. He has also consulted farmers seeking to change to organic production and advising on soil fertility. He is now a full-time permaculture consultant and stewards a 2.3-acre property with his family in Michigan.