Louis B. Thompson and Antonio P. Mallarino, Agronomy, Iowa State University, Ames, IA
There is strong interest on recovering nutrients from waste stream of industrial processing of crop biomass for bioenergy so it can be efficiently utilized as a fertilizer material. The objective of this study was to evaluate at the field the P availability for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] of P recovered as struvite [NH4Mg(PO4).6H2O] from waste produced by corn fiber processing for bioenergy. Conventional field plot trials were established at three Iowa locations with soils Marcus (Typic Endoaquolls), Floyd (Aquic Pachic Hapludolls), and Webster (Typic Endoaquolls). Soil-test P was low (8 to 12 mg kg-1 Bray-1 P, 15-cm depth) and pH was 5.5 to 6.4. Each trial was evaluated two years, with corn the first year and soybean the second. Treatments were 0, 12, 24, 36, 48, 72, and 120 kg P ha-1 as struvite (110 g P kg-1) or triple superphosphate (201 g P kg-1) broadcast before corn and incorporated into the soil by disking. Measurements were corn aboveground dry matter accumulation, P concentration, and P uptake at the V6 growth stage; corn and soybean grain yield; and post-harvest soil-test P in both years by the Bray-1, Mehlich-3, and Olsen tests. There were very large P rate effects on all plant and soil measurements at the three sites. However, there was no difference (P ≤ 0.05) between the two P sources for any plant or soil measurement in any site or year, not even for the lowest P rates. We conclude that P recovered as struvite from the waste stream of corn processing for bioenergy has crop availability similar to commonly used granulated inorganic P fertilizers.