Can California Produce Enough Compost to Meet Its Soil Health and Climate Goals?

People, Food and Land Foundation conducted a statewide assessment of compost feedstocks and processing infrastructure to answer this critical question.

The State of California is unique in its vast access to high-quality organic materials. Yet, only a fraction of that material, also called “feedstock,” is processed into soil-building amendments. We wanted to know:

How much compost could we create if we used all of it?
What’s stopping us?!

What We Found

Each year, California generates over 82.3 million tons of compostable organic material — from manure and prunings to food scraps and forestry biomass.

If all of these materials were composted, California could produce an estimated 33 million tons of compost each year — nearly one cubic yard per resident.

Feedstock Source Estimated Material Volume

Confined Cattle Manure 52.5 million tons

Forestry Biomass 14.3 million tons

Municipal Organics (e.g. food waste, paper, yard waste) 10.4 million tons

Agricultural Biomass (orchard prunings, seed waste) 5 million tons

According to the best available data, only 9.7 million tons of compostable organic materials are currently processes into compost annually.

This equates to approximately 5.6 millions tons of compost created each year.

Current Composting Capacity Sites Tons Processed / Year

Commercial Composting 70 5.3 million tons

Agricultural & Green Waste Sites 142 1.4 million tons

Dairy-Based Composting ~80 ~3 million tons

Community Composting ~220 ~2,900 ton

Conversations with practitioners and agriculturalists suggest that this number may be underestimated, particularly for dairies. However, there is still far more available feedstock than is currently being composted, and instead it is driving pollution across the state.

This difference is a massive untapped opportunity that calls for smarter planning, scaled infrastructure, and policy alignment.

What if we could close the loop?

What if we replaced synthetic inputs with recycled nutrients to rebuild soil and protect public health?

The Nitrogen Paradox

Each year, over 500,000 tons of synthetic nitrogen are applied to California croplands. Yet between 50–70% is lost to the air and water, resulting in contaminated drinking water and some of the state’s worst air pollution in the Central Valley.

Let’s do some back of the envelope math:

There are 8.5 million acres of irrigated cropland in California.
California agriculture applies approximately 514,000 tons of synthetic nitrogen per year.
Only 154,000–257,000 tons of nitrogen are actually needed to meet crop fertility needs.
California generates about 82.3 million tons of compostable organic material, which can make approximately 33 million tons of compost.
Applying 3 tons of compost per acre of irrigated cropland (about 25.5 million tons) annually would result in:
- Sequestering 186 million metric tons of CO2e over 10 years
- At least a 1% increase in soil organic matter over 10 years
- At least an additional 24 billion gallons worth of water-holding capacity
- At least 106,000 tons of plant-available nitrogen

Why Compost is Greater Than Synthetic Inputs

Short Story: The nutrients in compost do not behave the same as those in liquid fertilizer. Unlike synthetic fertilizers, compost binds nutrients to carbon and delivers them through microbial exchange. This:

Reduces leaching and runoff
Enhances nutrient uptake and plant health
Improves soil structure and long-term fertility
Improves the soil’s water-holding capacity
Improves the soil’s carbon storage capacity

Why It Matters

California’s Central Valley feeds the world, and yet it is also home to some of the nation’s most polluted air and water. Overuse of synthetic fertilizer and concentrated animal feeding operations (CAFOs) contribute to nitrate contamination, air pollution, and soil degradation. This pollution disproportionately affects low-income rural communities, harming the very people whose hard work keeps the nation fed.

At the same time, the state produces – and mismanages – enormous quantities of municipal, agricultural, and forestry materials that are rich in essential nutrients.

Pollution and Equity

One of the world’s major agricultural regions, California’s Central Valley, suffers severe rates of nitrogen pollution from excessive synthetic fertilizer use and concentrated animal feeding operations (CAFOs). Low-income, farmworker communities are disproportionately affected.

360,000+ tons of excess nitrogen enter groundwater every year
250,000+ residents have water in their homes that is contaminated with nitrates (source)
25–41% of California’s nitrogen oxide (NOₓ) emissions come from nitrogen-saturated soils (source)
Ammonia pollution and PM2.5 (i.e. fine particle) exposure from CAFOs, predominantly dairies, and biomass burning is linked to asthma, COPD, lung cancer, Type 2 diabetes, cognitive decline, depression, adverse birth outcomes, and increased risk of premature death (source)

As shown in CalEnviroScreen and other EJ mapping tools, these burdens are not equally distributed. They are concentrated in communities across the Central Valley, where multiple environmental burdens are compounded.

Resources

Review PFL’s resources listed below for more information and detail about the data and research related to this project.

Interactive Map:

Compost Inventory Map

Accompanying Data:

California Feedstock Inventory

California Compost Site Inventory

Data Gathering Methods

Additional Research and Whitepapers:

View our Full Systems Impact Presentation

Explore California Feedstock Inventory 2024 for calculations

Western Compost Trials – Real world results on compost’s impact across CA

The Chemical and Biological Benefits of Compost – by Dr. Alexia Cooper

Find other [resources on environmental justice and agricultural pollution in the Central Valley]

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