Date of Graduation

8-2023

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Wood, Lisa S.

Second Committee Member

Popp, Jennie S.

Third Committee Member

Drescher, Gerson L.

Keywords

Phosphorus; Runoff; Struvite

Abstract

Mined phosphate rock, used to produce phosphorus (P) fertilizers, is a finite resource. Struvite (MgNH4PO4 • 6H2O) that has been synthetically produced from a stock solution of known P and nitrogen (N) concentrations has been shown to be an effective, alternative fertilizer-P source for various crops. However, little is known about the runoff-water-quality implications from and the crop response to soil application of struvite created from an actual municipal wastewater source. This study consisted of two objectives: i) to evaluate the effects of soil [i.e., Creldon (Oxyaquic Fragiudalf), Dapue (Fluventic Hapludoll), Roxana (Typic Udifluvent), and Calloway (Aquic Fraglossudalf) series], fertilizer-P source [i.e., synthetically produced electrochemically precipitated struvite (ECSTsyn), real-wastewater-derived ECST (ECSTreal), chemically precipitated struvite (CPST), and monoammonium phosphate (MAP)], and water source (i.e., rain water, groundwater, and struvite-removed real wastewater) over time on runoff-water-quality parameters from laboratory-conducted, rainfall-runoff simulations, and ii) to evaluate the effects of soil (i.e., Creldon silt-loam and Calloway silt-loam series), fertilizer-P source [i.e., ECSTsyn, ECSTreal, CPST, MAP, and an unamended control (UC)], and irrigation water source (i.e., tap water and struvite-removed real wastewater) on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] growth and N, P, and magnesium (Mg) concentrations and uptakes in a 60-day, greenhouse potted-plant study. For Objective 1, mesh tea bags containing each soil-fertilizer treatment combination were rained on with each water source (Trial 1), incubated for 6 months, and rained on again (Trial 2) to evaluate runoff-water quality changes over time. In general, in both trials, runoff-water-quality properties from the struvite fertilizers (i.e., CPST, ECSTreal, and ECSTsyn) were similar to those from MAP. In Trial 1, runoff total P (TP) concentration differences (i.e., soil-fertilizer-water-type response minus the UC response minus the blank response) from ECSTsyn or ECSTreal were one to five times larger than MAP and CPST for all water-soil-fertilizer-P source treatment combinations, except for the Creldon soil-groundwater and Roxana soil-wastewater combinations. In both Trial 1 and 2, runoff TP decreased over time in all water-soil and soil-fertilizer-P source treatment combinations, except for in the Roxana soil-CPST treatment combination, where TP increased over time by 46%. For Objective 2, crop growth and N, P, and Mg concentrations and uptakes for the struvite treatments (i.e., CPST, ECSTsyn, and ECSTreal) were generally similar to MAP or at least 1.2 to 2.5 times greater than MAP. The ECSTsyn material commonly had up to five times greater N, P, and Mg concentration and uptake in corn and soybean than any other fertilizer-P source. Struvite-removed wastewater tended to result in N, P, and Mg concentrations, uptakes, and dry matter that were at least 1.3 times lower than tap water. Results showed that, despite having larger concentrations of many plant nutrients than tap water, struvite-removed wastewater does not appear to be a viable source of nutrients for corn or soybean growth. The similar water-quality and corn and soybean responses from the struvite fertilizers compared to MAP suggest that struvite has similar runoff-water-quality and agronomic implications as at least one widely used, commercially available, multi-nutrient fertilizer-P source.

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