Benefits of irrigating with wastewater

A recent study by Dr James Meyer, a private consultant, and Dr Rian Pierneef, a researcher in bioinformatics at the Agricultural Research Council’s Biotechnology Platform, found that wastewater from piggeries significantly increased the microbial diversity of soil. Pieter Dempsey spoke to the researchers.

- Pieter Dempsey

What prompted the research?

Dr James Meyer (JM): It was conducted to evaluate whether the positive effects of microbe addition described in international literature could be replicated locally, and thereby challenge the limits imposed in South Africa on the reuse of agricultural wastewater for irrigation.

Growing demand for food has resulted in greater use of inorganic fertilisers, often with adverse effects such as soil degradation, acidification and reduced soil organic carbon. It has also reduced the effectiveness of inorganic fertilisers and thus an increase in the use of organic fertilisers, either alone or in combination with inorganic fertilisers, to mitigate these adverse effects.

Could you explain the methodology and main findings of the project?

JM: The research was conducted in collaboration with members of the South African Pork Producers’ Organisation and the Biotechnology Platform at the Agricultural Research Council. Three types of soil samples were obtained from three commercial piggeries in different provinces.

Each piggery supplied soil irrigated with biodegradable wastewater from the piggery, inorganic commercial fertiliser, and neither (ecological buffer zones). Additional compliance monitoring data were also obtained.

Dr Rian Pierneef (RP): The microbial DNA was extracted from these soil samples employing the sequencing library of the 16S rRNA V3-V4 regions. A bacterial barcode was sequenced to identify the bacteria in the soil and give an overview of species and diversity. This indicated the beneficial traits they might possess to improve soil quality and increase plant growth. There were clear differences in the soil’s bacterial composition among the various locations and treatment areas.