What are you farming? You may say fruit, grain, vegetables, livestock or pasture, but stripped to the bare essence, everybody is actually farming carbon to nitrogen, or more specifically, the soil. This was the message of Nico Uys, operations manager of Ezolimo Organics, at the SA Olive Field Day, held near Wellington in the Western Cape in January.

Uys said most of South Africa’s soil had a carbon content of less than 0,5%, which means farmers are heavily dependent on external inputs to produce crops.

However, by increasing the carbon content of soil, farmers can improve the chemical, biological and physical structure of the soil, which translates into huge cost savings by improving nutrient retention and reducing the vulnerability of crops to pests and diseases.

Such an improvement also renders crops less vulnerable to climate shocks. The soil becomes like a sponge that is better able to handle rain during the rainy season, less prone to erosion and topsoil washing away during heavy rains, and able to hold more water during dry months.

Uys referred to research that found that the soil’s water-holding capacity could almost be doubled with every 1% increase in carbon. For instance, the water-holding capacity of 100kg soil could increase from 20ℓ to 40ℓ if the carbon content of this soil were increased from 1% to 2%. It would increase to 200ℓ if the carbon content of this soil was raised to 5%.

“South African farmers should aim to build their soil carbon levels to between 2% and 2,5%. Higher levels have been achieved in Mpumalanga and Limpopo, but it is difficult in drier parts of the country. Levels of up to 5% have been achieved in some wetter and cooler parts of the world.”

Building soil carbon levels

Various methods exist to build soil carbon levels, such as minimum disturbance of the soil; minimum to no-tillage; using mixed cover crops; mulches, compost and compost teas; adding microbes and bio-stimulants; and/or including an animal factor on a farm.

The trick, however, lies in the management of these tools. “People might claim that mixed cover crops are the solution to all problems because of the diversity they bring to the production system. But cover crops are not going to solve any problems without proper management.”

Uys added that starting off with six different cover crop species was difficult, and therefore advised farmers to start with one and then gradually build a mixture of crops as they became more proficient in the management of the crops.

The choice of cover crop depends on the production area, the soil and the goal with the crop.

“Choose a crop that will grow easily in your production region. For olives you would want to start with nitrogen fixers, such as legumes, of which more than 10 species are available.”

Uys warned farmers against the “blind” purchasing of new expensive equipment or solutions to build carbon levels, as what works on one farm might not be practical or feasible on another because of differences in the chemical, biological and physical properties of the soil, climatic conditions and production and management systems.

Instead, farmers should look at what they have available to work with on the farm and seek appropriate interventions. These should be tested on a small scale first and adapted to their unique conditions before being implemented on the whole farm.

Farmers should also shift their focus from crop health to soil health. Yet, to prevent the shift from having a negative impact on crop growth and yields, they should continue to look after the needs of the crops.

“Do leaf analysis to identify and fix nutrient imbalances suffered by the plant. Address nutrient shortages with foliar sprays while you are correcting soil imbalances and building soil carbon levels, as the soil is unable to hold onto nutrients when soil carbon levels are low.”

Plant health

Plants need carbon dioxide, oxygen, water, and energy from the sun for photosynthesis and optimal growth. An improvement in soil structure not only improves the water-holding capacity, as mentioned earlier, but also air movement within the soil.

Higher oxygen levels, in turn, create a more favourable environment for beneficial organisms, yet a less favourable environment for the development of root diseases, such as Pythium, Phytophthora and Verticillium, according to Uys.

Soil microbes require organic carbon compounds for growth and energy. They oxidise organic compounds from soil organic matter and generate carbon dioxide – more simply, they take in oxygen and release carbon dioxide, which plants then use for photosynthesis.

Uys pointed out that greenhouse producers in the Netherlands were way ahead of the rest of the world in understanding and using carbon dioxide. They pump carbon dioxide as a fertiliser into their greenhouses to improve photosynthesis, which in turn helps to accelerate vegetable growth by about 25%.

According to a study by Wageningen Economic Research’s energy monitor for Dutch greenhouse horticulture, Dutch greenhouse growers purchased 700 000t of carbon dioxide in 2022.

Uys said that US agriculture department researcher Rick Haney, who developed the Haney Test to measure soil health, estimated that plants could require up to 168kg of carbon dioxide per hectare a day.

The soil can supply from 33kg of carbon dioxide per hectare through microbial activity if the carbon content is around 1,5%, and up to 224kg if the carbon content is around 5%. Root respiration can supply even more.

Without carbon dioxide, about 10ha of oxygen would be required to produce carbon dioxide for 1ha of wheat.

Measurements

But how can farmers determine plant and soil health? Uys pointed out that plants used carbon dioxide and energy from the sun to produce sugar and oxygen during photosynthesis.

The measurement of the sugar content of plant saps in leaves, therefore, gives an indication of “how well the factory of the plant” is working.

“Dr Arden Anderson, a medical doctor who later became a soil scientist, said that the higher the sugar level, measured in Brix, the healthier and more pest and disease resistant the plant,” Uys said.

“He also came up with the idea that people are what they eat, and that depleted soils could not produce healthy food.”

The Brix for most olive trees with which Uys works averages between 12 to 15 on better-managed farms, but is around 6 to 7 on other farms. In some vineyards it goes as low as 4. The Brix levels for olives and wine grapes should ideally be 20 and above, according to him.

Besides measuring sugar levels, Uys suggested farmers make use of Haney’s Soil Health Test to give them an indication of the health of their soils. Unlike traditional soil tests, which measure the full nutrient content of the soil, this test gives an indication of what is available to plants.

The measurements include water-extractable organic carbon, water-extractable nitrogen, water-extractable organic nitrogen, microbial activity, the carbon-to-nitrogen ratio, inorganic nitrogen, potassium and phosphate, and organic acid-extractable aluminium, iron, and phosphate.

Uys said that the test could be used to compare the condition of two farms, assess a management practice, such as tillage versus no-tillage, cover crops versus no cover crops, or the use of manure or no manure, trouble-shoot problem areas within a field, and to make nitrogen, potassium, phosphate and lime recommendations.

Soil biology

When fixing chemical imbalances, farmers should familiarise themselves with the antagonisms that exist between different nutrients based on Mulder’s Chart. Uys explained that high availability and uptake of one nutrient interferes with the uptake of other nutrients.

High magnesium levels, for instance, would negatively impact calcium and potassium uptake, while increasing the plant demand for phosphorus and nitrogen.

High calcium levels, in contrast, would negative affect manganese, phosphate, zinc, boron, magnesium, iron and potash uptake.

Uys pointed out that bringing in biology on the farm through the addition of micro-organisms would help to fix chemical imbalances while helping to suppress harmful pests and disease.

For more information, email Nico Uys at [email protected], or phone him on 083 565 7337.