Degree Type


Date of Award


Degree Name

Master of Science




Soil Science (Soil Fertility)

First Advisor

Antonio P Mallarino


Wastewater from industrial or municipal water treatment plants requires P removal before being discharged to fields or surface waters. Therefore, there is interest in a sustainable recycling of this nutrient. The objectives of this study were (1) evaluate the chemical composition of dried mostly inorganic wastewater residuals after processing sludge from a pork packing plant for P reduction with biological treatment and Al2(SO4)3 14∙H2O (Al-P) or FeCl3 (Fe-P) addition, and (2) assess the P phytoavailability of these residuals compared with Ca(H2PO4)2 (MC-P) under controlled greenhouse conditions. The greenhouse study used topsoil from the Iowa soils Harps (Typic Calciaquolls), Nicollet (Aquic Hapludolls), and Zook (Cumulic Vertic Endoaquolls). Mehlich-3 soil P (measured colorimetrically), pH, organic C, and clay were 10 mg kg-1, 7.8, 40 g kg-1, and 34% for Harps; 3 mg kg-1, 6.0, 24 g kg-1, and 24% for Nicollet; and 16 mg kg-1, 7.1, 24 g kg-1, and 41% for Zook. Treatments replicated four times were three soils, three P sources, and total P amounts equivalent to 0, 25, 50, 100, 150, and 200 mg P kg-1 soil. Annual ryegrass (Lolium multiflorum) dry matter yield, P concentration, and P uptake were measured in four cuts.X-ray diffraction patterns and molar ratios of Al, Fe, and P extracted with ammonium-oxalate (AMOX) indicated the presence of small and not recognizable concentrations of crystalline Al, Fe, and P compounds in both residuals. Total P and P extractable by ammonium-citrate/EDTA (ethylenediamine tetra-acetic acid) (ACEDTA), 2% citric acid (2%CA), and water were (g kg-1) 116, 16.5, 89.7, and 0 for Al-P; and 102, 14.1, 37.1, and 0 for Fe-P. Therefore, the materials had no water-soluble P, and ACEDTA measured much less P than 2%CA. Estimates of the residuals P phytoavailability based on plant P concentration and P uptake relative to MC-P were 51, 52, and 35% for Harps, Nicollet, and Zook soils (46% on average), and for Fe-P were 17, 21, and 19%, respectively (19% on average). Therefore, ACEDTA (required by most states to label P fertilizers and amendments) grossly underestimated P phytoavailability of Al-P and Fe-P residuals (7-8% compared with MC-P), which was in contrast to 2%CA (43 and 18% of MC-P). Soil-test P measured after the final ryegrass cut showed that the Olsen method correctly assessed residual P from the three P sources but the Bray-1 and Mehlich-3 methods overestimated residual plant-available P from Al-P. Overall, the results are useful to make preliminary decisions about agronomic application rates for a sustainable recycling of P in these wastewater residuals. However, the relative efficiencies determined by this greenhouse study should be corroborated by evaluations at the field and for a longer time in soils with contrasting chemical properties.


Copyright Owner

Mariana Gomez Botero



File Format


File Size

67 pages