Plant availability of magnesium and phosphorus from struvite with concurrent nitrification inhibitor application

Abstract

Struvite (MgNH4PO4.6H2O) and nitrification inhibitors are applied to soils to, respectively, provide nutrients and reduce nitrogen (N) loss. Given its low N composition (5.7%) relative to that of phosphorus (P, 12.6%) and magnesium (Mg, 9.9%), struvite could be added to soil concurrently with N fertilizers as a source of P and Mg. Nutrient release from struvite could be impacted if nitrification of its ammonium component is reduced by a nitrification inhibitor. Accordingly, a pot trial gauged whether struvite‐fertilized ryegrass had comparable Mg or P uptake and shoot yields with treatments receiving conventional Mg and P fertilizers. Struvite precipitated from milk industry wastewater, or conventional fertilizers, were added to a soil–sand mixture of low fertility. The inhibitor dicyandiamide (DCD) was added to assess its effect on P uptake by ryegrass. Relative to Epsom salt, struvite led to increased Mg uptake without significantly affecting shoot biomass, indicating luxury consumption. Regarding shoot yield and P uptake, struvite was as effective as triple super phosphate. DCD significantly reduced P uptake in the first harvest; the inhibited nitrification of the ammonium is surmised to have diminished struvite dissolution. In later harvests, DCD led to a trend (albeit not statistically significant) of increased biomass; this N‐rich (66% N) compound was probably biodegraded and utilized as an N source. The impact of DCD on P uptake in this experiment was short‐lived. Nevertheless, DCD degradation occurs less rapidly in field conditions, potentially affecting early P supply which is vital for optimum yield.

Mycorrhiza Reduces Phosphorus Uptake from Struvite in Rye (Secale cereale L.) Plants

“…This is in line with Vogel et al (2015), where available P pools in soil increased after struvite application and struvite was considered to be an effective P source for several different plants. Recently, the struvite used in the present experiment was shown to be a very good source of P and Mg to ryegrass (Watson et al 2019). However, in our experiment, only a small proportion of applied P was found in the plant biomass at the end of our experiment, which may have been due to reduced plant growth as caused by other limiting nutrients or by satisfied P demand of the growing plants.…”

“…However, this was not observed in the roots, where control plants had a higher Mg:Ca ratio and the P:Mg ratio did not differ. The role of struvite as magnesium source requires more investigation as mentioned earlier (Watson et al 2019).…”

“…Each compartment received the equivalent of 100 mg P kg −1 sand in the form of struvite, which was 160 mg P and 320 mg P for each root/mycorrhizal compartment and each bulk soil compartment, respectively. The struvite was derived from dairy plant effluent by precipitation (Watson et al 2019). The crystalline struvite was evenly mixed in throughout the sand.…”

“…The use of alternatives like recovering P from waste can contribute to a more sustainable P-fertiliser use (van der Wiel et al 2020). Phosphorus fertilisers can be recovered in the form of struvite (MgNH 4 PO 4 •6H 2 O) from sewage sludge (Tarayre et al 2016), animal waste (Schoumans et al 2015) or dairy processing effluent (Uysal and Kuru 2013;Watson et al 2019). Even though water soluble P in struvite is often low, struvite or similar secondary minerals can be as effective as commercial P fertilizer (Muys et al 2021;Watson et al 2019) at the same time adding other valuable plant nutrients, such as nitrogen, magnesium or potassium (Watson et al 2019(Watson et al , 2020.…”

Hazenite: a new secondary phosphorus, potassium and magnesium fertiliser

“…Vogel et al (2017) reported the superior field growth of struvite-fertilised forage rye and sorghum to plants receiving triple superphosphate (TSP) and attributed this to a positive magnesium effect. Watson et al (2019) demonstrated struvite to effect a superior Mg uptake in ryegrass when compared with a commercially available magnesium sulphate fertiliser. Kataki et al (2016) noted Mg concentrations in soils might rise following repeated struvite amendment; this was acknowledged as potentially disruptive to Ca nutrition but beneficial to P uptake.…”