Agronomic use of ammonium-saturated zeolite in soilless cultivation: An alternative to reduce the risk of soil nitrogen contamination in Campania, Italy

Reducing the use of peat in growing media (GMs) for soilless production requires identifying alternative materials that support plant growth. In Campania, Italy, many livestock farms are located in zones vulnerable to pollution by nitrates of agricultural origin. Thus, researchers are exploring the use of waste from livestock farming in GMs for horticulture. This study aimed to assess the agronomic performance of GMs that contained compost from livestock farming and zeolitite (i.e., natural zeolite) that had been saturated with ammonium recovered from treating livestock manure. The growth of basil ( Ocimum basilicum L.) in a commercial GM (the control) was compared to that in three GMs that contained 50% peat (by volume), an increasing percentage of zeolite (10%, 20% or 30%) and the remaining percentage as compost. The experiments, conducted in a greenhouse over 9 weeks, showed that the increasing percentage of ammonium-saturated zeolite strongly increased electrical conductivity (from 2 to 7 mS cm −1 ), which could cause saline stress in crops. Nevertheless, this percentage was positively correlated with plant biomass, which was three times as high with 30% zeolite as with the control. Similarly, nitrogen-use efficiency was 2.5 times as high with 30% zeolite and 20% compost as with the control, while generating a high concentration of residual nitrate at the end of the experiment. These promising results highlight an opportunity for the circular economy by recycling livestock-farming-derived waste into horticulture GMs. However, medium- and long-term effects of these GMs must be investigated, particularly when ammonium-saturated zeolite is reused.