Dr Louis du Pisani shed light on why biodiversity is important, and its impact on soil, plant and animal health at the World Veterinary Association Congress held in Cape Town.
Soil health, veld health and animal health are interconnected: you cannot separate the one from the other.
This was the message from agri-consultant Dr Louis du Pisani during his presentation, ‘The rangeland microbiome and its benefits to ruminant productivity and health’ at the World Veterinary Association Congress held in Cape Town this year.
He said the role and importance of soil health in rangelands and grasslands only really started receiving attention in the past decade:
“Knowledge in this field has more than quadrupled over the past few years, and yet there still is a lot that is not understood because of the incredible complexity of the soil microbiome.”
Historically, plant organic matter content was seen as the biggest driver of soil health, but today the importance of micro-organisms is also recognised. It was also thought that these organisms were evenly distributed through the soil.
Today, however, we know they are mostly concentrated in the area between the roots of plants called the rhizosphere.
While every single organism plays a crucial role in creating a healthy biosystem, Du Pisani identified bacteria, mycorrhizal fungi and archaea as specifically important because of their influence on plant production.
The root microbiome
He explained that plants and soil micro-organisms were in a symbiotic relationship: the plants supply the micro-organisms with some of the energy they produced during photosynthesis while the soil micro-organisms provided various services in exchange.
Phosphorous and nitrogen, for instance, are inaccessible to plants in an inorganic state.
While the exact biochemical process is still uncertain, research has revealed that mycorrhizae transport these nutrients into the rhizosphere, where it and other micro-organisms turn them into water-soluble organic nutrients that can be used by the plants.
Du Pisani said it was likely that micro-organisms would be doing the same with other soil macro- and micronutrients, which raises questions about whether deficiencies are purely shortages of specific nutrients in the soil or an indication of problems in the microbiome.
In other words, whether something was preventing the micro-organisms from turning the nutrients into a plant-available form.
“Think about it. For years now we have been told that South Africa’s soils are deficient in phosphorous, while the phosphorous in fact is in a form that is unavailable to the plant. This might be the same for any other deficiencies, but we don’t know,” Du Pisani said.
He added that micro-organisms also released hormones, such as auxins, gibberellins, cytokinin, ethylene and abscisic acid, that helped to regulate plant growth and development, while a healthy diversity of soil micro-organisms helps to protect plants by keeping harmful soil pathogens in check.
In addition, soil micro-organisms played an important role in the exchange of water, minerals, and growth hormones between plants.
“We do not understand the mechanism but now know that mycorrhizae form a network between plants. This network allows plants to exchange ‘things’, like micro-nutrients, hormones and even water, of which they have an excess, for ‘things’ they need.
“We also know that plants with the same excesses are in competition with one another for their requirements.”
Du Pisani explained that mono-cropping was problematic because it meant that all the crops competed for the same resources and threw the ecosystem off balance by primarily attracting insects and other organisms that fed on these crops.
Another major problem was that it resulted in lower diversity in the soil:
“We know that the higher diversity in plants, the higher the diversity in the soil. You cannot only have nitrogen fixing plants in the soil, such as legumes, as the microbiome also needs other nutrients and carbon to flourish.
“You need diversity in the soil, as different micro-organisms play a different role in keeping the soil healthy.”
Most of the soil micro-organisms are concentrated in the area between the roots of the plant
Animal movement
But how do livestock fit into this? Animals benefit rangeland or grassland systems through their actions as they move across these lands.
“We don’t know if it is because of their saliva, urine, manure, or a combination of these, but we know that animals that are managed properly will benefit the soil microbiome,” Du Pisani said.
In response to a question about whether high-density grazing was superior to other grazing practices, he said that hardly any such studies had been done in South Africa, and the couple that were done did not reveal a significant difference between different grazing protocols.
“Farmers often say they follow a high-density grazing system. High-density grazing, however, is not a system but a management practice. Like all other management practices, it should be used correctly to produce the desired results.”
“For instance, animals should not be moved back to grazed land until the land has had time to fully recover. That is more important than the type of grazing practice used on a farm. Africa’s rangelands were developed through high-intensity grazing, but it cannot cope with high frequency grazing.”
Healthier animals
Animals derive various benefits by feeding on grasslands and rangelands that grow on healthy soils. Du Pisani said that a healthy rhizosphere resulted in higher and more stable forage availability and increased the nutrient status and the digestibility of forage on a farm.
It also improved rumen functioning and resulted in a healthier rumen biome.
“We don’t fully understand how this works, but see this happening in practice,” he said.
Forage grown on a healthy rhizosphere has the added advantage of causing minimal nutritional stress.
“By reducing nutritional stress, you get healthier animals with improved immune systems. They, subsequently, are less vulnerable to diseases and environmental stressors, which in turn helps to increase farm profitability.”
Du Pisani said there was a link between soil health and what people eat.
“This is not a new concept. The French biochemist and farmer, Andre Voisin, might not have understood or be able to prove it, but it is evident from the book he wrote in the 1950s, Soil, Grass and Cancer, that he knew this when he wrote that ‘animals and humans are biochemical photographs of the soil’.”
Email Dr Louis du Pisani at ldupisani@gmail.com.
