Use of nutrient-enriched zeolite (NEZ) from urban wastewaters in amended soils: Evaluation of plant availability of mineral elements

The usefulness of a nutrient-enriched zeolite (NEZ) obtained from simultaneous ammonium (NH₄⁺) and phosphate (PO₄^3-) recovery from urban wastewaters was evaluated as soil amendment through the early growth of sunflower (Helianthus annuus). The NEZ systems were applied to sandy (acid) and clayey (basic) soils from Mediterranean agricultural areas (Spain). Some plant growth indicators were measured: evapotranspiration, plant moisture content, plant biomass, root/shoot ratio, nitrogen and phosphorous uptake and the C/N ratio. The experimental data exhibited differences in the growth indicators for un-amended and amended soils. The addition of the NEZ system increase the plant water content of sunflowers grown on clay soils. The plant biomass of sunflower was improved by the incorporation of NEZ system in all treatments for the two soils studied. A reduction of the root/shoot ratio for the treatments of clay soil by application of NEZ systems were observed. The content of ammonium and phosphorous in tissues increased considerably with the addition of amendment material. Besides, the ammonium, nitrate and inorganic phosphorous in the post-test soils revealed that nutrients were still available for a second growth cycle. As demonstrated in previous work, the NEZ system releases nutrients continuously controlled by soil pH and mineral composition as well as the irrigation conditions provided. Therefore, this approach of amendment materials for soil seems to be a promising alternative for agricultural practice, where the dose selection must be balanced according to the plant's nutrient needs and soil properties by adjusting the growth conditions.