Evaluation of the Use of a Material with Struvite from a Wastewater Treatment Plant as N Fertilizer in Acid and Basic Agricultural Soils

Abstract

Struvite (MgNH4PO4 ∙ 6H2O) has been widely studied as an emerging recycled phosphorous fertilizer despite its low solubility. However, there are few studies on the use of this mineral as an N fertilizer. This article evaluates the use of two powder struvite-containing materials from wastewater treatment as an N fertilizer in agricultural soils. A 9-week soil incubation experiment was conducted to compare the effectiveness of this mineral as an N fertilizer in two soils with different pH values (8.2 and 6.7), using two different doses and a control soil. The use of these materials has a positive effect on soil fertility, especially in acidic soils where struvite seems to be more soluble. Thus, struvite can be a potential N fertilizer for agricultural soils and can promote circular economy opportunities for the wastewater industry, especially in acid soils (concentrations of mineral N between 453–339 mg/kg were obtained in the mixtures with acid soil, and values between 408–212 mg/kg in the mixtures with the basic soil after 6 weeks of soil incubation). However, associated with this process, an increase in soil salt content was observed (EC values reaching 3.9 dS/cm in mixtures with the acid soil and 2.8 dS/cm in the mixtures with the basic soil after nine weeks of soil incubation). Therefore, this parameter should be controlled in the case of continuous applications of the amendments, especially in conditions of poor drainage and/or non-percolating water regime, since it can be a limiting factor in crop development. These processes should be studied in detail in the future considering that the N soil cycle has a significant impact on soil chemistry and fertility and on the soil microbiological community.

Soil Chemical Property Changes over Time from Struvite Compared to Other Fertilizer-Phosphorus Sources in Multiple Soils

“…Both aforementioned studies agreed that soil NH 4 -N mineralization via nitrification to nitrate was the reason for the decreased NH 4 -N and increased NO 3 -N over the soil incubation periods. Other potentially lesser contributory factors to the degree of NH 4 -N nitrification may have been due to slight initial differences in soil pH, soil texture and cation exchange capacity, SOM, and initial NO 3 -N and NH 4 -N concentrations in the incubated soils [33] [53] [54].…”