Agronomic effectiveness of nitrogen and phosphorus recovered from swine manure

New technologies have been developed to extract and recover manure nitrogen (N) and phosphorus (P) that can be upcycled as substitutes for conventional fertilizers. Yet, there are uncertainties over the agronomic effectiveness of these recovered nutrients. In a greenhouse study, we evaluated annual ryegrass (Lolium multiflorum Lam.) response to recovered N (RN), conventional N (CN), recovered P (RP), and conventional P (CP) in four nutrient combinations: CN + CP, RN + CP, CN + RP, and RN + RP at five N rates: 0, 23, 46, 92, and 184 mg N kg⁻¹ soil; and three P rates: 0, 39, and 78 mg P kg⁻¹ soil. Results showed a synergistic response to N and P, where dry matter yield and nutrient uptake increased with both nutrients application. Under CP, ryegrass supplied with 92 and 184 mg N kg⁻¹ of CN produced 16%–35% more dry mass yield than RN. In contrast, ryegrass dry mass yield under RP was 17%–114% greater with RN than CN. Ryegrass dry mass yield under CP was 17% greater with CP than RP at 78 mg P kg⁻¹ soil, but RP produced 27%–66% more dry mass yield than CP under RN. There was no difference in soil inorganic N between the two N sources, but Mehlich-1 soil test P was less in RP than CP treated soil. The combination of RN and RP was an effective fertilizer blend for substituting CN and CP. This finding is critical for the advancement of the new circular nutrient economy.