Written by Freda Burden

Imagine trying to grow vegetables in beach sand. This is the challenging reality for gardeners in the Cape Flats. The area is located on the outskirts of Cape Town and lies on sandy, excessively leached soils which do not support bountiful vegetable growth. This is because sandy soil dries out quickly, is very low in nutrients and is easily eroded by wind or rain. To improve the fertility of soil in the Cape Flats the sand needs to be amended with organic matter, like manure or, as was the focus of the project described below, biochar.

In 2023, SouthSouthNorth initiated a friendly research project to test whether applying biochar to the sandy soils of the Cape Flats, could improve the yields of food-bearing plants growing in backyard and community gardens. The project was conducted in collaboration with Abalimi Bezekhaya, a longstanding community organisation who nurtures micro-farmers across the Cape Flats townships to grow vegetables organically.

Biochar and its Potential Value

Biochar is a charcoal-like substance that is made by smouldering plant matter. When dug into soil, biochar has the potential to improve agricultural productivity while also trapping carbon in the ground for up to thousands of years. This means biochar is an organic soil amendment that can improve food security while at the same time regulating the impacts of climate change.

The impact of biochar on soil and plants can be positive, negative or neutral, depending on a range of variables including what the biochar is made from and how it is applied. However, research has indicated that biochar appears to be particularly effective at improving the fertility of sandy and acidic soils because it increases their water and nutrient holding capacity.

Producing biochar is an ancient indigenous technique that has been used by agricultural communities in Africa for centuries. In contemporary Africa, biochar might be able to serve as a cost-effective resource for improving the quality of soil and thereby improve crop yields. If farmers produce their own biochar it can function as a cheaper and more ecologically sound alternative to chemical fertilisers.

The Relationship between Inequality and Soil Quality

Healthy soil is critical for climate regulation and sustaining life on Earth. Yet, access to good soil, and the benefits it provides to people, are not equally distributed.

The neighbourhoods that exist on the sandy soils of Cape Town’s, Cape Flats were created by South Africa’s apartheid government to marginalise communities of colour by locating them on the urban periphery, away from economic opportunities and quality public amenities, including green public spaces like community gardens.

Residents of the Cape Flats are more likely to be excluded from accessing food, especially wholesome and nutritious food, due to an array of intersecting food security barriers that exist in Cape Town’s food system. One of these barriers is the arid ground that characterises the Cape Flats. In the city that is a poster child for inequality, the state of the soil underlying the Cape Flats contributes to the large disparities in access that exist across Cape Town.

Project Context in Kuyasa

This biochar-testing project took place in Kuyasa, Khayelitsha. A low-income neighbourhood on the Cape Flats.

Kuyasa had been the site of the first registered Gold Standard ‘Clean Development Mechanism’ project under the United Nations’ Kyoto Protocol. In 2005, SouthSouthNorth initiated the implementation of a low-carbon housing development in Kuyasa. The project installed solar-heaters, ceilings and energy efficient light bulbs at 2,100 houses in the neighbourhood. As a result, Kuyasa households reduced spending on coal-fired electricity, their indoor air quality was improved and jobs were created for residents of the neighbourhood.

In 2021, following exacerbated food insecurity brought about by the COVID-19 lockdown restrictions, the project developer decided to use some of the carbon revenue earned from the sale of the project’s carbon credits to set up food gardens in the area. The biochar testing research aimed to build on this work by investigating a way to improve food security in Kuyasa while also reducing global carbon emissions.

Through improving the agricultural productivity of the sandy soil, biochar could be a resource for bolstering food security in the area, both by increasing the availability of food grown at gardens in the neighbourhood and by strengthening the economic viability of being a small-scale urban farmer on Cape Town’s outskirts.

How Were the Biochar Testing Experiments Set Up?

With the cooperation of Abalimi Bezekhaya’s network of farmers, ten biochar-testing experiment sites were set up. Bell pepper seedlings were planted in three different kinds of soil patches at each garden site. The soil patches were either:

1. Untreated
2. Treated only with biochar
3. Treated with a pre-mixture of biochar and sheep manure

The two experimental soil treatments had been donated to Abalimi Bezekhaya by SouthSouthNorth. A part of the function of this research project was also to test the effects of these donated soil treatments.

Both the biochar-based soil treatments used in this experiment were made from Black Wattle wood by a producer in South Africa’s Eastern Cape. Black Wattle, scientifically known as Acacia mearnsii, is an invasive tree species in South Africa. It competes with and replaces indigenous grasslands and riverine species.

What were the results?

From the project’s small study group, the following findings were made:

Bell Pepper Yields

The experiments showed that the plants growing in biochar-only treated soil would, on average, yield 45.3% more bell peppers than those in the control group. While the plants growing in the biochar and sheep manure pre-mixture treated soil would yield around 72.5% more bell peppers than the same plants grown in untreated soil.

Soil Moisture

Soil humidity readings, recorded with an instrument called the ZD-03, showed that on average the donated biochar on its own marginally decreased (by 4.1%) the detected water content of the gardens’ soils. While the application of a pre-mixture of biochar and composted sheep manure slightly increased (by 7.2%) the detected soil water content of the same gardens.

It might be that the porous nature of biochar and its capacity to bind and store water molecules meant more water was sequestered in the biochar-only soil patches. Making less water available in the surrounding area and thus less water could be detected by the ZD-03 in these patches compared to the patches that were treated with the combination of biochar and manure.

Fertilising a brighter tomorrow!

For gardeners on the Cape Flats to be able grow their vegetable bounties, they need to transform the sand in their yards into fertile soil. Our experimental findings suggest that adding biochar or manure is one way to achieve this. In the process, a little bit more carbon could be trapped, and a few more bodies could be nourished. Progress towards a more prosperous future can be made by fertilising one garden at a time.

Read the full report here.