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Is Struvite a Viable Phosphorus Source for Soybeans?

Fertilizers used for crop production comprise a significant portion of the total cost to produce most crops. In the case of phosphorus [P] fertilizers that are needed and used for soybean production in the U.S., 1) the cost has risen over the last few years, and 2) P fertilizers applied to cropland in this country have been a significant contributor to the decline in surface water quality.

Presently, the primary source of P fertilizers is rock phosphate [RP]. However, this P source is finite–in fact, some sources estimate that it will be gone in 50 years. Also, the U.S. has only a small reserve of RP. Most [~80%] of this P source is in northern Africa, which means that its availability to U.S. farmers is subject to the vagaries of world politics.

Recently, there has been increased interest in reclaiming P from wastewater sources to provide a sustainable source of P-fertilizer as well as reduce P enrichment in surface waters. Struvite [MgNH4PO4⋅6H20–magnesium ammonium phosphate] is the common name for a P-containing material that can be created from P-containing wastewater, and it is surmised that this P source could have value as an agricultural fertilizer. That is the premise behind research with struvite that was conducted by scientists at the Univ. of Arkansas to determine if this material can replace commonly-used fertilizers as a P source for crops. Results from that research follow.

In an article titled “Corn and soybean response to wastewater-recovered and other common phosphorus fertilizers” by Ylagan et al. [Agrosyst. Geosci. Environ. 2020;3:e20086,], results from research that was conducted to determine how struvite compared to other forms of P fertilizers when applied to soybeans are reported.

•    Objective of the study was to determine the effects of electrochemically precipitated struvite [ECST–crystalline form], chemically precipitated struvite [CPST–pelletized form], diammonium phosphate [DAP], monoammonium phosphate [MAP], rock phosphate [RP], and triple superphosphate [TSP] on corn and soybean in a greenhouse pot study. DAP, MAP, RP, and TSP are commonly-used P fertilizers.

•    Struvite-P treatments, and particularly ECST, were as good as or better at effecting positive plant responses in both corn and soybeans as were common P fertilizers.

•    These results point to 1) using struvite as a recycled P-fertilizer, 2) improving wastewater quality by removing the struvite-P, and 3) using struvite-P to provide a sustainable P-fertilizer source.

In an article titled “Soybean growth and production as affected by struvite as a phosphorus source in eastern Arkansas” by Omidire et al. [Crop Sci. 2023;63:320-335,], results from research that was conducted to determine how struvite affected soybean growth and development when compared to that resulting from fertilization with other P sources are reported.

•    In this field study that was conducted on a P-deficient silt loam soil, the objective was to evaluate the effects of ECST and CPST relative to the commonly-used P fertilizers DAP, TSP, RP, and MAP on soybean growth and yield, and the resulting economics.

•    Averaged across the 2 years of the study, the wastewater-recovered struvite material ECST was just as proficient at supporting soybean growth and yield as were the commonly-used P fertilizers.

•    These results support the findings of the greenhouse study in the previously-cited article–i.e., struvite has the potential to be a viable alternative P-fertilizer for soybean production in the Midsouth.

•    The current cost effectiveness of struvite as a P fertilizer depends on increased soybean yield resulting from its use. However, this is likely to change since current P-fertilizer sources are finite and thus are subject to price increases, whereas struvite recovery is sustainable and thus should have a stable price structure once a stable market for the material has been established.

In an article titled “Wastewater-recycled struvite as a phosphorus source in a wheat-soybean double-crop production system in eastern Arkansas” by Omidire and Brye [Agrosyst. Geosci. Environ. 2022;5;e20271,], results from research that was conducted to determine the effect of struvite on wheat and soybeans grown in a doublecrop system are reported.

•    The premise for conducting the research was that the majority of the current P-fertilizer is from mined RP, which is a finite resource. With an increasing global population, alternative and sustainable P sources are important to ensure global food security.

•    The objective of the 2-year field study conducted on a silt loam soil was to evaluate the effects of CPST vs. TSP on soybean and wheat grown in a wheat-soybean doublecrop production system in Arkansas.

•    Results from this research substantiate the use of CPST as a potential alternative P-fertilizer for crop production in the Midsouth.

All of the above positive results from research with struvite-P lead to the following questions. 1) Can struvite-P be economically created in an amount/at a scale that will provide a viable and stable source of P-fertilizer for Midsouth crops? 2) Will the creation and use of struvite-P be cost competitive in both the short- and long-term with that of common P-fertilizer sources now being used? 3) Will wastewater treatment facility managers/operators be willing to invest in and install the necessary apparatuses to create enough struvite to meet the P demands of agricultural producers? The answers to these questions will determine if/when struvite-P will or will not be a viable alternative to current P-fertilizer sources. However, since current P-fertilizer sources are finite, there likely will be a time in the near future when it is decided that struvite-P will necessarily become a significant P-fertilizer source for crop production.

Go to an Apr. 2022 article titled “Agronomic response to struvite as an alternative fertilizer-phosphorus source” by Leslie Johnson and a Mar. 2023 article titled “Struvite seen as good alternative for phosphate in crop fertilizer in Arkansas field study” by John Lovett for summaries of the results from the above research, comments by the reports’ authors about the potential utility of struvite as a P-fertilizer source for Midsouth crops, and lists of publications that report results from additional Arkansas studies with struvite.

Composed by Larry G. Heatherly, Apr. 2023,