Date of Graduation

8-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Brye, Kristofor R.

Committee Member

Roberts, Trenton L.

Second Committee Member

Greenlee, Lauren F.

Keywords

Column leaching; Environment; Soil and water quality; Soil fertility and crop response; Struvite; Wastewater

Abstract

Phosphorus (P) is a vital resource that is finite and only mineable in raw-material form in a few countries worldwide. Struvite (MgNH4PO4·6H2O) is a mineral that can be produced from wastewater that may provide a promising alternative source of fertilizer-P for crop production, but comprehensive characterizations of struvite behavior in various soils and responses of various crops are necessary. This study aimed to determine the (1) leaching potential, (2) vertical soil profile-P distribution, (3) wheat (Triticum aestivum), corn (Zea mays), and soybean (Glycine max) response, and (4) soil property changes over time of electrochemically precipitated struvite (ECST) compared to that of chemically precipitated struvite (CPST), monoammonium phosphate (MAP), triple superphosphate (TSP), and an amended control (UC) in loam (L), silt loam (SiL), silty clay loam (SiCL), and sandy loam (SL) soils from Arkansas (AR-L, -SiCL, and -SiL), Missouri (MO-SiL 1 and 2), and Nebraska (NE-SiL and -SL). Leachate properties differed (P < 0.05) from their UC among soils and fertilizer-P sources over time. Leachate pH differed among soils, ranging from a change of 0.1 to 1.0, while water-soluble (WS)-P also differed (P < 0.05) among soil-fertilizer-P-source-time combinations, but only in the AR-L, where TSP (2.0 to 6.6 mg L-1) consistently had larger WS-P difference than ECST (-0.04 to 3.1 mg L-1) in weeks 1 to 3. Vertical soil profile WS-P concentrations from the two struvite’s generally did not differ (P > 0.05) and were similar to that of MAP, but greater than for TSP in the top 6 cm in four of the six soils. For all three crops, more than 50 % of the 35 plant properties per crop differed (P < 0.05) among fertilizer-P sources within soils, while the other plant properties differed among soils or among fertilizer-P sources. Wheat, corn, and soybean dry matter (DM) response to ECST across crops and soils was complex. However, crop response from ECST was generally similar or greater than for CPST, MAP, TSP, and the UC across all soils, except for belowground wheat DM in the AR-SiL and MO-SiL 2. Similarly, the ECST had similar or larger tissue nutrient concentrations and uptakes to that for CPST, MAP, TSP, and the UC. Aboveground nitrogen (N), -P, and -magnesium (Mg) tissue concentrations and uptakes from ECST were generally similar to that for all soil-fertilizer-P source combinations. All but one (i.e., WS-Mg) parameter differed (P < 0.05) among fertilizer-P sources within soils over time in a soil-incubation study. Soil-fertilizer combinations generally had an acidifying effect over time. Water-soluble soil-P change relative to the initial for ECST was generally similar or larger than for the other fertilizer-P sources. Results show that the use of recovered struvite materials as a fertilizer-P source has significant potential for a wide range of crops, while being environmentally protective, meaning recovered from wastewater and only partially soluble in water allowing for greater soil retention than MAP and TSP, thus reducing the risk of eutrophication in surface waters or P-loss through leaching. Further research is needed to fully understand the plant response to struvite use as a fertilizer-P source and the effects of its long-term use on soil properties and microbial communities, but the results so far are promising.

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