Struvite (NH₄Mg(PO₄).6H₂O; P₂O₅ = 29%) is produced at waste water treatment works as a means of removing phosphate and so reducing release of P by discharge of treated waste waters to surface and groundwater systems.  At present, struvite is not widely produced, and its potential for use as a field crop fertiliser has yet to be fully explored (NB Johnston & Richards, Soil Use and Management, 19, 45-49, 2003, used struvite in their comparison of precipitated P sources on grass growth and P offtake).    This paper presents the results of a pot-trial investigation of the potential of struvite as a source of P for the cultivation of wheat under conditions appropriate for Libyan desert soils (Wady Barjuj project, Fazzan Region, southern Libya).

To reproduce as closely as possible in northern England the environmental conditions at Wady Barjuj, wheat (two varieties: Karem (hard) and Marshush (soft)) was cultivated in an artificial sandy soil with irrigation under glass between January and June.  The effect of struvite and dicalcium phosphate (DCP) as phosphate sources (application rate 140 kg/ha P₂O₅ equivalent), was compared for yields (wheat biomass and grain quantity) and for agronomic parameters (e.g. grain quality, P uptake).   All treatments and a P-free control were supplemented with K as KCl and N as ammonium sulphate (prior to tillering) as solids, supplying N as urea with irrigation water and micronutrients as a foliar spray after tillering.

Use of struvite consistently increased yields compared with DCP in terms of seed weight, straw weight, plant height and plant dry weight (Table 1).    This general pattern was observed in all experiments, irrespective of application method (band vs broadcast; ground vs coarse granules).   Addition of extra N as ammonium sulphate to DCP treatments to compensate for the presence of N within struvite removed the significant difference to DCP indicating that as sources of P the two materials were similar.

Leaf P content for each variety of wheat was raised by up to 50% by the addition of both DCP and struvite (Table 1).   Leaf Mg contents reached 94 mg/kg for struvite applications (Table 1). 

This study is the first, we believe, to investigate the response of wheat to the application of struvite, and confirms the value of this material as a source of P. It is comparable to DCP as a source of P but has the additional advantage of containing available N.   In the context of water treatment as a means of recovering phosphate, this study demonstrates the potential value of struvite as a possible commercial by-product with applications as a fertilizer.

	-----  Hard wheat  -----			-----  Soft wheat  -----
	control	DCP	struvite	control	DCP	struvite
Seed weight (g/pot)	2.6	15.1	17.0	2.7	13.8	15.5
Straw weight (g/pot)	4.8	9.7	11.9	5.1	10.3	12.3
Plant height (cm)	26.5	33.7	36.7	29.4	32.1	35.6
Plant dry weight (g)	1.38	1.91	2.05	1.56	2.38	2.71
Leaf P content (mg/kg)	0.17	0.38	0.39	0.13	0.35	0.35
Leaf Mg content (mg/kg)	74.9	68.6	94.0	81.4	84.1	89.5

Table 1: Summary of growth parameters for wheat pot trials with struvite and dicalcium phosphate (DCP).