Ever thought of putting sewage on your plants? Scientists say thermally conditioned sewage sludge serves as an excellent fertilizer to improve soil properties. This was recently published in the open-access journal Frontiers in Nutrition. The major advantage over commercial fertilizers? Sustainable re-use of essential and finite phosphorus resources. Phosphorus is a key nutrient for all living beings. When deficient in the diet, it severely compromises human health, and when deficient in agriculture, it restricts crop productivity. Without phosphorus, there can be no food production.

As the source of phosphorus is non-renewable phosphate rocks, there is a strong need for increased recycling to ensure phosphorus security. Efficient use and reduced environmental dissemination of phosphorus throughout the food system is needed to secure the ability to feed a growing global population.

As technological improvements increased the phosphorus content of sewage sludge, it now is a readily available alternative to commercial fertilizers in agriculture. To assess its effectiveness, Andry Andriamananjara from the University of Antananarivo (Madagascar) and his colleagues used a phosphorus radiotracer technique to measure the availability of phosphorus for plants in thermally conditioned sewage sludge. 

They grew ryegrass in pots filled with soil that underwent isotopic P-labelling, and added either no fertilizer, thermally conditioned sewage sludge as fertilizer, or commercial triple superphosphate fertilizer. Shoot and roots were harvested at fixed intervals, and their radioactivity was analyzed to measure phosphorus uptake. 

As expected, fertilizer application increased shoot biomass significantly over the harvest time, while only a trend towards an increase in root biomass was found. The addition of fertilizer increased phosphorus uptake by the plants. This wasn't only because the fertilizer offered an additional phosphorus source, but also because the plants increased their soil exploitation.