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Update to data summary in SCOPE Newsletter 121 on struvite effectiveness as fertiliser.

Since publication of the summary of recent field and pot trial test data of struvite as a fertiliser, published in SCOPE Newsletter n° 121, four further papers have been communicated to ESPP. With the data reviewed in SCOPE 43 (2001) and in SCOPE 121 (June 2016), this brings to over 50 the number of publications to date.

This considerable data converges to confirm that struvite is an effective fertiliser for a wide range of crops, both in acidic and also neutral or slightly alkaline soils.

Additionally, a report by Ehlert et al. (Wageningen, 2013), financed by the Netherlands Ministry for Economy, summarises the legal issues relating to marketing struvite as fertiliser (progressively changing waste regulation, fertiliser regulation). This report notes that in many cases the phosphates precipitated from waste streams are not pure struvite (magnesium ammonium phosphate), but can include significant levels of potassium, calcium, magnesium, aluminium or iron phosphates. The report includes tables summarising levels of different elements (N, P, Mg, K, Ca) and levels of heavy metal contaminants in over 25 different precipitated phosphates.

This report shows that care is taken when referring to “recovered struvite” to ensure that the product is indeed struvite, and not a mixture of other phosphates which may not have the same fertiliser value (possibly lower nutrient plant availability or not so well studied to date). The report indicates that struvite products should also be differentiated between whether or not they are susceptible to contain pathogens (precipitation from waste streams such as manure or sewage, or high pH in precipitation process which will kill pathogens).

Additional evidence of struvite fertiliser value
The new papers presenting data on struvite as a fertiliser are:

Grunert et al. (publication pending, presented at WEF/IWA Nutrient Removal and Recovery Denver, July 2016). Pot trials (5 litre rhizotrons) using tomato (Solanum x.) and lupin (Lupinus angustifolius) from seed to 5 weeks, comparing an organic fertiliser, recovered struvite and no fertiliser. Struvite gave significantly increased leaf area and fresh weight compared to no fertiliser (8-10x increase for tomato, c. 25% increase for lupin). Greater increases were given by the organic fertiliser, but this contained e.g. 5% potassium and 2% sulphur as well as higher nitrogen (and six times lower phosphorus) than struvite, so that results are not comparable.

Degryse et al (same conference as above) carried out petri dish solubility tests of different struvites and six week pot trials with wheat (Triticum aestivum) in soils pH 5.9 and 8.5. Results show that some recovered struvites with excess magnesium oxide (MgO, used in this case as a reagent in the recovery process) is significantly less soluble in soil. Pot trial results show very similar results from ground (<0.15mm) commercial mono ammonium phosphate (MAP) and ground commercially recovered struvite (Ostara CrystalGreen) mixed throughout the soil, whereas if only one c. 50 mg granule of fertiliser was placed in the pot then in alkali soil MAP was more effective. These results suggest that granular struvite releases nutrients more slowly in alkali soil than does MAP, but that this can be redressed by grinding and mixing into the soil.

Robles (same conference as above) tested wastewater recovered struvite (Lequia pilot struvite reactor, Girona – Tarrago et al. 2016) to triple super phosphate (TSP) in 40-day pot trials with maize and lupin, soil pH 4.8, with two different nitrogen sources: ammonium (acidifying) and nitrate (alkalizing). Struvite gave the same biomass as did TSP for lupin, and significantly higher for maize. Ammonium gave in most cases higher biomass and higher P uptake than did nitrate.

Kern, Heinzmann et al. (2008 but missing in previous reviews) tested wastewater recovered struvite (Berlin Wasser, Wassmannsdorf) in 8-week pot trials on maize and wheat (sand and nutrient solution). P uptake rates of 67-87% were shown. A no-fertiliser control was included but no comparison to commercial P fertiliser.

‘MagAmp’ = struvite, a much sought-after specialist fertiliser
We have now also obtained copy of an older paper (Tawagan & Boodley, 1963). These authors tested one application of Grace Co. ‘MagAmp’ (commercial struvite) for pot-plant Pointsettias, grown from cuttings for three months, using one dose of the struvite in several different pot plant soils / peats / perlite / vermiculite (pH not specified), plus added potassium nitrate to provide N and K. Conclusions were that single in-pot applications of struvite resulted in good quality plants.

‘MagAmp’ fertiliser was struvite (magnesium ammonium phosphate). The production from phosphoric acid was patented (patent US4153441). The name trademark filed by W.R. Grace Co. in 1962, and subsequently was sold on to Hyponex Japan and then Sumitomo Corp. Grace Co. documentation from 1966 presents MagAmp as “A non-burning solid fertilizer, only slightly soluble in water, for nursery stock and fruit trees. Available in two formulations, 7-40-6 and 8-40-0”. Including recently, MagAmp and struvite are recommended fertilisers in publications for specialist products, for example tomotaoes in “Hydroponics: A Practical Guide for the Soilless Grower” (J. Benton Jones, CRC 2005), Jr. Struvite mixed with ammonium sulphate was being sold as “Enmag” into the 1990’s in the UK. Until 2013, MagAmp was still being sold by FukuBonsai, Hawaii, and was a sought-after fertiliser for bonsai specialists.

Degryse F. et al., “Dissolution rate and agronomic effectiveness of struvite fertilizers – effect of soil pH, granulation and base excess”, Plant Soil 2016

Grunert O. et al. “Struvite and Organic Fertilizer Impacting The Rhizosphere Microbial Community, Nutrient Turnover and Plant Growth Performance” WEF/IWA Nutrient Removal and Recovery Denver, July 2016

Kern J, Heinzmann B. et al., “Recycling and Assessment of Struvite Phosphorus from Sewage Sludge”, Agricultural Engineering International CIGR Ejournal. Manuscript number CE 12 01. Vol. X. December 2008

Robles A. et al. “Effectiveness of Recycled Phosphorus as Struvite is Modulated by the Nitrogen Source Applied” WEF/IWA Nutrient Removal and Recovery Denver, July 2016

“Wettelijke Onderzoekstaken Natuur & Milieu. Opname van struviet als categorie in het Uitvoeringsbesluit Meststoffenwet”, P. Ehlert, T. van Dijk, O. Oenema, Wageningen Werkdocument 332, funded by the Netherlands Ministry for Economics, 2013

“Results of one-shot feeding for pointsettias”, Florists’ Review, 133, p28-30 and 80-81, September 1963, A. Tawagen & J. Boodley, not available online.

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