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

• Published in: Soil use and management 2019-12, Vol.35 (4), p.675-682
• Main Authors: Watson, Conor, Clemens, Joachim, Wichern, Florian, Nicholson, Fiona
• Format: Article
• Language: English
• Subjects: Ammonium; Ammonium compounds; Biodegradation; Biomass; dicyandiamide; Fertility; Fertilizer industry wastewater; Fertilizers; Inhibitors; Magnesium; Mg uptake; Milk; Mineral nutrients; Nitrification; Nitrogen; Nutrient release; Nutrients; P uptake; Phosphates; Phosphorus; ryegrass; Sandy soils; Soil; Soil fertility; Soil mixtures; Soils; Statistical analysis; Struvite; Uptake; Wastewater; Yield
• ISSN: 0266-0032; 1475-2743
• DOI: 10.1111/sum.12527

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.