S13 - Session P2 - Use of recovered struvite and ammonium nitrate in two fertigated edible crop rotation cycle in soil

Authors: Mar Carreras-Sempere *, Miriam Guivernau, Marc Viñas, Rafaela Cáceres, Carmen Biel

Struvite and ammonium nitrate (AN) are products obtained from widely studied processes to remove phosphorous (P) and nitrogen (N) from waste streams (wastewater treatment plants, slurries from livestock, etc.). To boost circularity in horticulture, these recovered products should be applied to edible crops. Therefore, two fertigated crop rotation cycles in soil were evaluated to determine the efficiency of both recovered products as raw materials for a nutrient solution (NS) manufacture. These products, used as P and N sources, and a conventional synthetic fertilizer treatment (control) were compared in terms of yield, nutrient uptake and environmental impact. This study is first in implementing struvite as the unique source of P fertilizer in fertigation in soil crops. Satisfactory results of struvite solubilization, tests in order to use it in fertigation, were obtained. Results show that both nutrient-recovered products can be used as fertilizers in NS, due to their similar or higher yield production compared to control treatment for different parameters and crops (fruit quality and P and N uptake in tomato, lettuce and broccoli crops). However, the AN treatment showed a lower yield than control due to the different ammonium tolerance among tomato varieties. Chemical soil analysis at the beginning and the end of the crop's rotation indicate a non-accumulation of nutrients and heavy metals. While the effect of the mineral nutrition on the soil-rhizosphere microbiota over two growing seasons revealed no changes in soil alpha-diversity (Shannon diversity index) compared to the initial samples, the different NH 4 + /NO 3 - ratios in the NS affected the microbial richness and the ammonia-oxidizing community abundance and composition, with a clear enrichment of Nitrospira phylotypes during fertilization. These results give deeper insights into the future potential utilization of nutrient-recovered products, especially after the publication of the future EU-wide quality standards for struvite as fertilizer.