Compost vs. Fertilizer, What are the Differences?

A common question among growers is: what is the difference between compost and fertilizer? How can I best deliver the necessary nutrients? Will yields be affected? Do I need both, one, or the other?

These questions have become even more significant with the recent surge in fertilizer prices driven by the worldwide fertilizer shortage. Faced with these immediate challenges, growers are intent on understanding options and alternatives regarding fertilizers. Could manure or compost be a viable route for those who have counted on fertilizers in the past?  

What is the Difference between Compost and Fertilizer?

Applying compost and applying fertilizer are two common approaches to delivering nutrients to plants. While they may seem similar—and can, at times, be complementary—there are some key differences.

Compost is a mixture of decomposed organic matter, from living and dead materials like manure, food scraps, and leaves. Once broken down, compost becomes a nutrient-rich amendment used to feed the soil and promote plant growth.

Fertilizer is a natural or synthetic substance that, when applied, directly supplies plants with nutrients. Natural fertilizer, or organic fertilizer, is extracted from animal and plant byproducts. Examples include manure and bone meal. Synthetic fertilizers are chemically manufactured compounds, like ammonium nitrate and potassium sulfate.

Fertilizer Shortage

Fertilizer prices have shot up an average of 70% from last year due to a global fertilizer shortage. The shortage is caused by various factors like the rising price of natural gas, a source for certain nitrogen-based fertilizers. With Russia as the world’s largest exporter of fertilizers, the situation has been worsened by sanctions and export cuts resulting from Russia’s invasion of Ukraine. COVID-19 pandemic restrictions, which have thrown global supply chains into a frenzy, have also complicated matters.

With soaring fertilizer prices, food security becomes a pressing issue. For growers who depend on fertilizers to boost harvests, applying less chemical fertilizer generally means producing lower crop yields. For consumers, lower production could mean seeing higher food prices at grocery stores.

As growers navigate the global fertilizer shortage, many are looking at alternate methods. Some farmers are turning to renewable fertilizers, like manure or compost, in place of chemical fertilizers.

Compost vs Fertilizer, Which is Best?

With a global fertilizer shortage at hand, the opportunity to adapt and transition to a system that requires little to no chemical fertilizer has come into focus for many. While continuous application of fertilizer is effective at helping plants in the short run, turning to compost can help to rebuild the overall health of soil and increase yields.   

Benefits of Compost

Compost is a useful way to repurpose organic matter—like manure, fruit and vegetable scraps, grasses, and other living or previously-living material—into a rich amendment that goes into the soil. In many ways, composting encourages a circular approach, where nutrient-rich and biodegradable resources that a grower or community may already have can be put back into the earth, creating a fertile growing medium for seasons to come.

Adding compost restores overall soil health, thereby promoting healthy plant growth. The addition of compost improves the soil’s physical, biological, and chemical properties, allowing for multiple benefits:

• Improved soil structure
• Better water infiltration and retention
• Less soil erosion/loss and runoff
• Enhanced nutrient supply and uptake by crops
• Greater diversity of soil microbial life to help plants grow and resist disease
• Greater long-term resiliency in face of challenges like drought, wildfires, and floods

While exact amounts can vary, a good-quality compost typically contains a wide-ranging spectrum of plant nutrients, including the three main fertilizer nutrients: nitrogen (N), phosphorus (P), and potassium (K). In addition, compost provides micronutrients and trace minerals that chemical fertilizers do not have.

For growers with large plots of land, a common concern is that applying great quantities of compost can be costly. In this scenario, a compost extract can be created as a method to spread a set amount of compost over a large area, reducing cost while providing similar positive benefits. This extract—typically made by agitating a bag of compost in a tank of water—creates a liquid full of nutrients and microbes, which can be distributed or sprayed over large areas.

As soil biology and function improve with the application of compost, the microbes in the soil help make existing phosphorus in the ground and nitrogen in the air plant-available. In this way, growers can work towards a reduction in fertilizer application over time, thereby reducing input costs. Some farmers have even radically reduced or completely eliminated nitrogen fertilizers once their soil biology was restored.

Impact of Fertilizer

Fertilizers can be a useful way to supply targeted chemical elements to plants in the short run. While they’re used primarily to directly deliver nutrients to plants, a high dependence on chemical fertilizers can harm soil biology and cause soil to become less fertile over time. In some cases, overapplication of fertilizer can bring about unintended consequences like contamination of air and water supplies. Overfertilizing can also lead to plant damage, harm the plant’s ability to take in water, and affect yields.

Looking Ahead

As a global fertilizer shortage persists into the unforeseeable future, opportunities to try alternate methods of tending to crops and land emerge.

When it comes to compost vs fertilizer, compost could be a solution that growers explore to achieve better soil health and long-term resiliency. While both methods provide nutrients to plants, compost nourishes the soil. Through this nourishment, the soil becomes a robust growing medium that promotes healthy plant growth and crop yields.

Written By Jennifer Ho

Jennifer Ho (she/her) is a UC California Naturalist and advocate for healthy soils and ecological regeneration. She enjoys cooking, hiking, and nurturing a small urban food forest and native plant garden at her home.