“Soil health research is a can of worms,” says Dr Nigel the programme manager for the Deciduous Fruit Producers’ Trust (DFPT’s) soil health research programme. “This is because fruit producers are overwhelmed by the vast array of products available today, together with all the conflicting claims that go with them. “However, it’s good that producers are more aware of the importance to farm in a sustainable manner and understand that using fewer chemicals is better in the long run.”
A lthough little scientific information is available on soil health, many people have strong opinions on the subject. Due to its complexity and because most research is being done in field trials where external factors can influence the results of experiments, the research will have to be long-term, Dr Cook says. He explains that the uniqueness of the DFPT programme lies in its multidisciplinary approach – the research team consists of soil scientists, horticulturists, pathologists, microbiologists, nematologists and entomologists.
This approach also allows knowledge to be shared between different disciplines. “Research on cover crops for apple application can, for example, draw on the work already done for cover crops in vineyards,” Dr Cook explains. The importance of soil health research S oil health research is necessary as it covers a vast number of interacting variables. These include soil’s ability to hold and release nutrients and water, promote root growth, maintain microbial biodiversity, respond to management and resist degradation.
According to Dr Cook, only a few facts about soil health are known and accepted scientifically – more carbon is needed in South African orchard soil; microbial activity and diversity need to be increased to improve soil health; mulches improve water-use efficiency; and soil improvement is a slow process. he main questions the DFPT programme addresses are – what is soil carbon and how can it be increased? What soil microbes need to be increased and how? And what is the physical and biological reaction of a plant to healthy soil?
Dr Cook explains that carbon is fixed during photosynthesis when plants bind carbon dioxide, water and soil minerals to form plant tissue. When the plant dies, it decomposes and fungi and bacteria live off it. It’s at this stage that the explanations of modern science become vague. he DFPT programme is research-based, but focuses strongly on industry interaction. Dr Cook explains, “fine balance needs to be maintained, where scientists are allowed to work without being bullied by the commercial sector, but at the same time, are doing research that has the potential for practical usage.”
H e stresses that researchers need to publish their work so that it can be peer-reviewed. “But industry interaction is equally important, as it will keep the programme relevant to the industry’s needs. So the researchers aim to report to the interest groups at least four times a year,” Dr Cook explains.
Apples and cover crops
Two current projects promising to deliver exciting results are an apple replant disease (ARD) trial and a soil cover crop management trial. ARD causes poor root growth in young apple trees which are planted on previous apple sites. ARD is specific to apples and persists in the soil even after the trees have been removed, says Louise van Schoor, a researcher from the Agricultural Research Council and member of the programme.
Methyl bromide is used as a sterilisation agent when establishing new apple orchards, but the apple replant trial is searching for organic alternatives. Recently compost extracts and teas have been advocated as inoculants to stimulate and enhance soil microflora. However, little research has been done to confirm or quantify these benefits. The DFPT study aims to evaluate the potential use of compost in combination with soil inoculants and beneficial bacteria, as a viable alternative for ARD control.
“We’re also examining the effect of these biological amendments on soil and plant nutrition, as well as on microbial community activity,” Louise says. “We’re trying to establish correlations between these factors and tree performance.” The soil management trial is experimenting with different organic cover crops and cover crop systems in apple orchards. Dr Cook explains that the traditional practice of keeping the bank free of any vegetation is now being questioned. “Weeds can be a cheap source of soil carbon if managed correctly,” he says. Contact Nigel Cook on (021) 870 2900. |fw
