Ferments and Biochar: A Practical Guide to Utilizing Local Resources

Aerial picture of a production site for plant ferments, fish ferments, and inoculated biochar in Puerto Rico. Video footage from Syntropic Agriculture: An Approach to Building Food and Farm Resilience in Puerto Rico, NCAT.

By Daniel Hoffman, Omar Rodriguez, and Luz Ballesteros Gonzalez
NCAT Agriculture Specialists

Abstract

The challenge of resource scarcity is familiar to many farmers. Imported goods such as manufactured fertilizers, herbicides, and pesticides are not always accessible or affordable for producers who live in remote locations. Finding local materials that may be considered waste and turning them into soil amendments creates abundance amid scarcity. This publication highlights agricultural inputs farmers and ranchers can produce with the excess materials at hand through fermentation and biochar production.

Contents

Introduction
Fermentation as a Process for High-Value Farm Inputs
Fermentation Recipes and Application
Biochar
Conclusion
References
Further Resources

Introduction

Off-farm inputs such as fertilizers, herbicides, and pesticides are often expensive, and access to these products may be unreliable due to a farm’s location or because of disruptions to the supply chain. Finding local so-called “waste” materials and transforming them into usable resources creates abundance amid scarcity and enhances a farm’s resilience. Vegetation and fish waste can be converted into biochar and fermented fertilizer, valuable amendments that support plant and soil health.

This publication explores how to create and use fermentation products and biochar on the farm. We will share recipes for producing plant and fish ferments and key insights on application, storage, and nutrient dynamics. We will also look at the ways biochar can improve soil health and fertility, and ways to enhance biochar for maximum benefits. Whether you farm in a resource-limited region or you are simply looking to reduce your reliance on store-bought fertilizers, fermentation and biochar are accessible practices for small and medium-scale farmers and ranchers.

Fermentation as a Process for High-Value Farm Inputs

Fermentation is a simple way to transform excess organic materials such as plant residues, manure, or fish waste into readily available sources of nutrients for plants and soil microbes. Many microbes respire oxygen, just like humans. However, in the absence of oxygen, some species of bacteria, yeast, and fungi can break down sugars and convert them into energy. This anaerobic process, sometimes referred to as anaerobic digestion, is fermentation. Byproducts of fermentation include lactic acid and acetic acid, as well as ethanol. These acids lower the pH of the material, inhibiting microbial growth and supporting food preservation. Ethanol also reduces microbial growth and assists in food preservation.

An Age-Old Practice

People around the world have used fermentation for thousands of years to transform and preserve food. The Natufian people who lived in the Levant are believed to have been fermenting beer around 13,000 years ago (Liu et al., 2018). Many other ancient peoples enjoyed fermented alcoholic beverages as well, from fermented rice, fruit, and honey in China (7,000 B.C.E.), to beer in Mesopotamia (7,000 B.C.E.), to wine in western Iran (6,000 B.C.E.), to fermented agave by the Otomi people in Mexico (2,000 B.C.E.) (Escalante et al., 2016; Ray et al., 2024). Cheese, another product of fermentation, was documented in Mesopotamia, in what is modern-day Iraq, between 6,000 and 7,000 B.C.E. (Ray et al., 2024). If you have eaten foods like sauerkraut, kimchi, yogurt, or sourdough bread, you are part of a long tradition of consuming fermented foods.

Many cultures have also used fermentation to break down organic materials to preserve plant nutrients and make them more accessible to animals, plants, and microorganisms. Silaging, the process of fermenting grass to preserve it for animal feed, is in the Old Testament book of Isaiah, which was written around the 8th Century B.C.E. (Cai and Ataku, 2025; Woolford and Pahlow, 1998). Kunapajala, a fermented liquid manure, is referenced in Vrikshayurveda, an Indian book whose title translates to “the science of plant life,” written around the 10th century C.E. (Nene, 2018; Thakur et al., 2025).

Aerial picture of Finca Tintillo, a farm in Carolina, Puerto Rico run by José Ángeles Ríos. Video footage from Syntropic Agriculture: An Approach to Building Food and Farm Resilience in Puerto Rico, NCAT.

Fermentation on the Modern Farm

The process of fermenting agricultural residues or other organic materials is simple and requires minimal time commitment. Given the right conditions, many ferments can also be stored for months. If you use the proper ratio of ingredients, you can make a relatively consistent product. Because it requires minimal time and resource investment, fermentation is an ideal process for small or medium-scale producers interested in making fertilizers and amendments that are inexpensive and accessible.

Fermented products contain plant available nutrients and beneficial microbes that support plant resilience. As microorganisms convert sugars to energy through fermentation, they also break down nitrogen-rich materials such as proteins into their constituent parts (peptides and amino acids). Microorganisms and plants use these smaller nitrogen-rich molecules as building blocks for growth, making these molecules an important source of nitrogen (Jones and Darrah, 1994; Farrell et al., 2011; Blachier, F., 2025; Tegeder and Rentsch, 2010). In addition, amino acids and peptides have been shown to have beneficial effects on plants, even at a low rate (Costa et al., 2024), including increased nutrient uptake, increased nutrient use efficiency, and increased resilience to salinity, heavy metals, nutrient stress, and water stress (Calvo et al., 2014; Colla et al., 2017).

Fermentation products are particularly useful during soil preparation, early crop development, and flowering phases. They can be applied as foliar sprays, root drenches, or incorporated into compost teas. They can increase the presence of plant beneficial microorganisms and microbial enzyme activity, which improves nutrient absorption and availability and reduces the need for synthetic fertilizers (Kolambage et al., 2024; Vassileva et al., 2021).

Fermentation Recipes and Application

In fermentation, producers combine organic materials such as food scraps, green plant matter, crop residues, or fish waste with a sugar source, typically molasses or raw cane sugar, to provide energy for microbial activity. Sometimes microbial inoculants such as Lactobacillus species can be added to accelerate the fermentation process. The mixture ferments for 7–30 days (recipes will vary), depending on the ambient temperature and desired microbial profile. The result is a potent, nutrient-rich liquid that farmers can apply directly to plants or soil.

Recipe for Plant Ferments

To begin fermenting plant matter on the farm, farmers can follow a simple recipe.

Materials:

• Container: clay, plastic, glass, ceramic, or stainless steel
• Towel or heavy cheesecloth
• Strainer
• Storage container with lid

Ingredients:

Equal parts by weight:

• Fresh, unwashed, green plant material (e.g., comfrey, sweet potato vines, pig weed, water hyacinth, purslane, etc. – whatever you have in abundance in your locality)
• Brown sugar

Instructions:

1. Mix and coat as much of the plant material with sugar as possible, to speed up the osmotic process and help to draw fluids out of the plant material.
2. Pack the mixture into a container that won’t react with the ferment, such ceramic, glass, plastic, or stainless steel, and leave loosely covered with a towel or heavy cheesecloth.
3. Place the container in a shaded location for 7–10 days to ferment. In general, the optimal temperature range is between 60 and 85 degrees. Fermentation will speed up with higher temperatures and slow down with lower temperatures. The ideal temperature will vary based on the bacterial species that colonize your ferment. Look for bubbles to confirm that fermentation is occurring. These can usually be seen by the second day.
4. A fermentation is finished, according to Miller et al. (2013), when “the plant material floats and the liquid settles at the bottom (note: if too much brown sugar was used, this separation is not distinct); there is a light alcohol smell due to breakdown of chlorophyll; and the liquid tastes sweet, not bitter.”
5. Strain out the solids with a colander, strainer, or mesh, and discard.
6. Store the strained liquid in sanitized containers in a cool, dark place. Close the storage containers loosely because the solution is alive and will continue to produce gases.

The nutrient profile of the resulting ferment will depend on the original nutrients in the feedstock used. For example, fermenting leguminous plants results in a fertilizer with higher nitrogen levels than a ferment that uses grass as a feedstock. Fermentation conditions can be further optimized for nitrogen production by purchasing specific microorganisms for inoculation (Kolambage et al., 2024; Vassileva et al., 2021).

It is worth noting that almost any excess and readily available plant material can be feedstock for fermentation. The parts of plants with high proportions of cellulose and lignin, like wood, are harder to break down and will slow the fermentation process. Conversely, selecting plants with high levels of readily available sugar, starch, and other nutrients will promote microbial growth and speed up the process. Leaves, non-woody stems, flowers, and immature fruit all make good feedstock.

How to Apply Plant Ferments

For optimal results, use a blend of both fresh and aged ferments (more than one month old) in your preparations. When ready to do your application, dilute the ferment at a ratio of one part fermented plant juice to 500 parts water (1:500 is approximately 1 tablespoon per 2 gallons or one cup per 31 gallons). However, under certain conditions, a more diluted solution—between 1:800 and 1:1,000—is recommended to prevent potential plant damage such as leaf burn. You might need to dilute the solution more if:

• Combining more than three ingredients in a single application (a “cocktail” of inputs)
• Applying during periods of hot weather
• Using fermented plant juice that is over a year old, as it may have become more concentrated over time.

Apply the solution to crops once per week, preferably in the early evening to prevent leaf burn, particularly when applying ferments as foliar amendments. It can be administered in several ways: as a foliar spray, or watered directly onto the soil, focusing on the root zone (Miller et al., 2013).