Technical Yearbook 2023

Management of biological soil health should aim to minimise the percentage of pests/pathogens in the soil, while increasing the number of beneficial organisms in the soil. Furthermore, it should focus on maintaining healthy plants to minimise the effect of pests and pathogens on plants. The key to a fully functioning effective soil food web is diversity. Different organisms have different life history characteristics, life cycle duration, physiological and behavioural attributes, as well as their adaptation to varying conditions. Their dispersal and exploitation of different areas throughout the soil profile, associated with differing moisture, aeration, texture and chemistry are indicative of the delivery of complementary services within a particular functional guild rather than being in competition with each other. Although these organisms deliver a similar function within the soil food web, their adaptations to differing conditions and niches provide resilience to the soil food web. If environmental conditions affect the growth and development of one type of organism, the entire service within the soil food web is not lost as there are other organisms contributing to the same function. Management interventions should be targeted at the lower trophic levels of the soil food web as this is the source of the soil food web. If the food is available (plants, root exudates, bacteria and fungi) and the environment is conducive (physical and nutritional properties of the soil is well maintained), the higher-level organisms within the soil food web will proliferate. To promote diversity in below-ground organisms, there must be aboveground diversity. Organisms in the soil respond to root exudates. A variety of root exudates will stimulate a variety of organisms in the soil. 28 If these plants are hosts to different pathogens, diversity can also contribute to the reduction of pathogen levels as it decreases the ability of the pathogen to find a host. 12 Aboveground diversity can be increased through the use of multi-species cover crops. Multispecies cover crops have the ability to increase microbial diversity, while minimising the increase of soil-borne pathogens and increasing populations of beneficial microbes by increasing plant functional groups richness. The choice of the crop within the mix can also help to suppress plant pathogens through direct effects such as the ability of brassicas to suppress fungal pathogens and promote disease-suppressive bacteria. Native plants may also further promote beneficial soil microbiota. 28 Table 1 shows the effects of different groups of cover crops on soil microorganisms. When using cover crops, ensure that the soil pests and pathogens are identified prior to planting so that host crops to those pathogens are avoided or minimised within the mix.

Cover crops can either be used as living crops with the aboveground biomass being removed or the organic matter can be incorporated into the soil. The resultant effect on the soil will be different. The composition of the decomposing plant litter has been shown to affect both the activity 1 and the community structure of soil microbes. 6 Other management interventions include the addition of organic amendments. A meta-analysis was conducted in 2018 14 of 690 independent organic amendment studies globally. The organic amendment increased the amount of soil organic carbon by 38%, total nitrogen by 20%, microbial biomass carbon by 51% and microbial biomass nitrogen by 24% compared with mineral-only fertilisation. Organic amendments also increased the soil microbiome enzyme activity in terms of soil hydrolytic C acquisition (39%), N acquisition (22%), P acquisition (48%) and oxidative decomposition (58%). There are also many beneficial soil microorganisms specifically targeted toward root health that are commercially available for addition within agricultural systems. Despite the focus on increasing diversity and beneficial organisms within a soil, one must not lose sight of the fact that the objective is to maintain the balance of beneficial and pathogenic organisms within the soil. Commercial agriculture is an unnatural system and as such the number of pathogens will increase. Numbers of pathogenic organisms within the soil must therefore constantly be monitored and managed such that the numbers remain within acceptable ranges and do not negatively affect root or plant growth. For optimal root development, all three aspects of soil health must be managed optimally. The key thread that runs throughout all areas is that of monitoring and applying appropriate management interventions, based on data. In order to manage soil and roots effectively, the objectives for all three facets of physical, chemical and biological properties must be set, all three properties must be measured and based on objectives and measurement, appropriate management interventions must be made. This is a continuous process as the soil is a living organism that is constantly evolving in response to change. Acknowledgements The author would like to acknowledge her co-authors of the paper titled: A review of management practices impacting root health in sugarcane. 26 The framework of this write-up is largely based on that paper.  References https://www.wineland.co.za/managing-for-optimum-root health/

For more information, contact Prabashnie Ramouthar at prabashnie@nemlab.co.za.

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TECHNICAL YEARBOOK 2023