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Agronomic Response to Struvite as an Alternative Fertilizer-phosphorus Source

Purpose

As a primarily mined material, the global reserve of phosphorus (P) is finite and running out. Consequently, inorganic, commercial fertilizers are becoming more expensive. Chemical engineering techniques have been developed and are being actively researched to recover P from wastewater sources in the form of struvite (MgNH4PO4 · 6H2O). Many wastewaters contain elements such as P and nitrogen (N) in various forms that could be recovered and beneficially recycled as fertilizer nutrients. Recovering nutrients, such as P, from wastewaters and/or treating wastewaters to the point they could be safely recycled back into the environment could have a tremendously positive impact on any agricultural activity as well as receiving waters.

Arkansas has a documented significant geographic nutrient imbalance, where the row-crop-dominated region of eastern Arkansas has a severe nutrient deficiency, particularly for P, which routinely requires commercial P applications to supply crop needs for optimum production. Thus, eastern Arkansas is an ideal setting for testing the effectiveness of recovered nutrients from wastewaters as fertilizer sources, especially P, for various row crops, namely rice, corn, and soybeans. A sustainable, wastewater-recovered source of P, in the form of the mineral struvite, would be a critical advancement in the long-term viability of P availability, P-source options, and use as a fertilizer in P-deficient soils used for crop production.

What Did We Do?

Figure 1. Image of the moist-soil, plant-less laboratory incubations with various soil and fertilizer-P treatment combinations.

Various studies were conducted to evaluate the behavior of struvite in different soils and crop response to struvite as compared to other commonly used, commercially available fertilizer-P sources [i.e., monoammonium phosphate (MAP), diammonium phosphate (DAP), triple superphosphate (TSP), and rock phosphate (RP)]. Two struvite materials were tested, a chemically precipitated struvite (CPST) created from real wastewater treatment plant effluent and an electrochemically precipitated struvite (ECST) created in the laboratory with an innovative electrochemical approach.

Figure 2. Image of the column-leaching experimental set-up with various soil and fertilizer-P treatment combinations.

In the laboratory, a series of plant-less soil incubation experiments were conducted in several different agricultural soils to evaluate the behavior of struvite and the other fertilizer-P sources as they solubilize. Soil pH, water-soluble and plant-available P, magnesium (Mg), calcium (Ca), iron (Fe), nitrate and ammonium concentrations were measured over a 4- to 9-month period in moist/aerobic and saturated/flooded/anaerobic soil conditions (Figure 1). A column study was also conducted to evaluate the effects of fertilizer-P source, including ECST and CPST, on P-leaching characteristics over time in multiple soils (Figure 2).

Figure 3. Image of the rainfall-runoff experimental set-up.

Additionally, a rainfall-runoff simulation experiment was conducted to evaluate the effects of water source (i.e., rainfall, groundwater, and struvite-removed wastewater) and fertilizer-P source on runoff water quality parameters (i.e., pH, electrical conductivity, and P, N, Mg, Ca, and Fe concentrations) in various soils (Figure 3).

Figure 4. Image of rice growing in the greenhouse in response to various fertilizer-P sources with chambers in the tubs to measure greenhouse gas emissions.

In the greenhouse, several potted-plant studies were conducted for 60-90 days evaluating above- and below-ground plant response to ECST, CPST, MAP, DAP, TSP, RP, and unamended controls in rice, corn, soybeans, and wheat. Studies were also conducted to evaluate the effects of fertilizer-P source (i.e., ECST, CPST, DAP, TSP, and an unamended control) on greenhouse gas emissions (i.e., CO2, CH4, and N2O) from flood- and simulated-furrow-irrigated rice (Figure 4).

In the field, two-year studies have been conducted in soil having low soil-test-P to evaluate the effects of fertilizer-P source (i.e., ECST, CPST, MAP, DAP, TSP, RP, and an unamended control) on above- and below-ground dry matter and tissue P, N, and Mg concentrations, aboveground tissue P, N, and Mg accumulations, and yields in rice, corn, and soybeans, as well as soil P concentrations in corn and soybeans (Figure 5).

Figure 5. Image of a field study with soybean and corn grown in response to various fertilizer-P sources.

What Have We Learned?

For the moist-soil incubations, averaged across fertilizer sources, differences in water-soluble soil P concentration [from their initial concentrations] differed among soils over time and, averaged across soils, among fertilizer sources over time. In addition, averaged across time, Mehlich-3-extractable soil P concentration differences from their initial concentrations differed among fertilizer sources within soils. For the flooded-soil incubations, averaged across fertilizer sources, the change in soil pH from the initial differed among soils over time. In addition, averaged across soils, the change in water-soluble soil P concentration from the initial differed among fertilizer sources over time. Results from the plant-less soil incubation experiments show that many elemental soil concentrations, namely P, and soil pH differed among soil-fertilizer-P-source combinations over time. However, in general, the two struvite materials (ECST and CPST) behaved similarly to one another and behaved similarly to at least one other commonly used, commercially available fertilizer-P source without any large, unexpected outcomes across several different agricultural soils with varying soil textures. Struvite appears to relatively similar soil behavior as other commercially available fertilizer-P sources.

For the greenhouse study, no differences were identified in soybean plant properties. However, corn plant properties and corn and soybean elemental tissue concentrations differed (P < 0.05) among fertilizer amendments. Total corn dry matter from ECST did not differ from that from RP and TSP and was 1.2 times greater than that from CPST Belowground corn dry matter from ECST was 1.9 times greater than that from CPST, TSP, DAP, and the unamended control treatments Corn cob-plus-husk dry matter from CPST and ECST were similar. Corn belowground tissue P concentration from CPST did not differ from that from DAP, TSP, and MAP and was 1.4 times larger than that from ECST. Corn cob-plus-husk tissue P concentration from ECST was similar to that from MAP and DAP and was 1.2 times larger than that from CG. Corn stem-plus-leaves tissue P concentration from ECST differed from that from all other treatments and was 1.8 times greater than that from the unamended control. Struvite appears to be a viable, alternative fertilizer-P source.

For the 2019 rice field study, neither above- or belowground P, Mg, and N tissue concentrations differed among fertilizer sources. For the 2019 corn field study, neither above- or below-ground P, Mg, and N tissue concentrations differed among fertilizer sources. For the 2019 soybean field study, neither aboveground Mg or N nor belowground P, Mg, and N tissue concentrations differed among fertilizer sources. However, aboveground tissue P concentration was greater from ECST than from RP and the unamended control.  For the 2020 rice field study, aboveground dry matter and aboveground dry matter P, N, Mg concentrations did not differ among fertilizer sources. However, rice grain yield from ECST was similar to that from CPST, but both were lower than from TSP. Aboveground Mg uptake from ECST was greater than that from CPST. For the 2020 corn field study, total aboveground, cob/husk, and stalk/leaves dry matter, aboveground P, N, and Mg concentrations and uptake, and belowground P and N concentrations did not differ among fertilizer sources. However, corn yield was larger from ECST than from all other fertilizer treatments, which did not differ among themselves. Belowground Mg concentration was numerically largest from ECST among all fertilizer-P treatments and was significantly greater than that from MAP, DAP, and TSP. For the 2020 soybean field study, neither aboveground dry matter nor yield differed among fertilizer sources. Similar to greenhouse results, struvite appears to be a viable, alternative fertilizer-P source for multiple agronomic crops, including rice, corn, and soybean.

Results from a greenhouse trial in 2021 showed that, across 13 sample dates over a nearly 4-month period evaluating the effects of fertilizer-P source on greenhouse gas fluxes and emissions from flood-irrigated rice, CO2 fluxes were unaffected by fertilizer-P source, but differed over time, while both CH4 and N2O fluxes differed among fertilizer-P treatments over time. Furthermore, results showed generally lower CO2, CH4, and N2O fluxes from ECST than from the other fertilizer-P sources and numerically lower CO2 and N2O season-long emissions from ECST than from the other fertilizer-P sources, while CH4 emissions from ECST were numerically lower than from CPST in flood-irrigated rice. Electrochemically precipitated struvite may have potential to reduce greenhouse gas emissions from flood-irrigated rice.

Future Plans

Future plans include additional laboratory rainfall-runoff simulation experiments, greenhouse potted-plant trials, and field studies to evaluate the effects of real-wastewater-derived struvite compared to other commonly used, commercially available fertilizer-P sources on soil and plant response as well as greenhouse gas emissions.

Authors

Presenting author

Lauren F. Greenlee, Associate Professor, Pennsylvania State University

Corresponding author

Kristofor R. Brye, University Professor, University of Arkansas

Corresponding author email address

kbrye@uark.edu

Additional authors

Lauren F. Greenlee, Associate Professor, Pennsylvania State University

Niyi Omidire, Post-doctoral Research Associate, University of Arkansas

Tatum Simms, Graduate Research Assistant, University of Arkansas

Diego Della Lunga, Graduate Research Assistant, University of Arkansas

Ryder Anderson, former Graduate Research Assistant, University of Arkansas

Shane Ylagan, Graduate Research Assistant, University of Arkansas

Machaela Morrison, Graduate Research Assistant, University of Arkansas

Chandler Arel, Graduate Research Assistant, University of Arkansas

Additional Information

Anderson, R., K.R. Brye, L. Greenlee, and E. Gbur. 2020. Chemically precipitated struvite dissolution dynamics over time in various soil textures. Agricultural Sciences 11:567-591.

Ylagan, S.R., K.R. Brye, and L. Greenlee. 2020. Corn and soybean response to wastewater-recovered and other common phosphorus fertilizers. Agrosystems, Geosciences & Environment 3:e20086.

Anderson, R., K.R. Brye, L. Greenlee, T.L. Roberts, and E. Gbur. 2021. Wastewater-recovered struvite effects on total extractable phosphorus compared with other phosphorus sources. Agrosystems, Geosciences & Environment 4:e20154.

Anderson, R., K.R. Brye, L. Kekedy-Nagy, L. Greenlee, E. Gbur, and T.L. Roberts. 2021. Total extractable phosphorus in flooded soil as affected by struvite and other fertilizer-P sources. Soil Science Society of America Journal 85:1157–1173.

Anderson, R., K.R. Brye, L. Kekedy-Nagy, L. Greenlee, E. Gbur, and T.L. Roberts. 2021. Electrochemically precipitated struvite effects on extractable nutrients compared to other fertilizer-P sources. Agrosystems, Geosciences & Environment 4:e20183.

Omidire, N.S., K.R. Brye, T.L. Roberts, L. Kekedy-Nagy, L. Greenlee, E.E. Gbur, and L.A. Mozzoni. 2021. Evaluation of electrochemically precipitated struvite as a fertilizer-phosphorus source in flood-irrigated rice. Agronomy Journal 114:739–755. DOI: 10.1002/agj2.20917

Brye, K.R., and L.F. Greenlee. 2022. What is struvite and how is it used? Blog post for Soil Science Society of America’s “Soils Matter” blog (https://soilsmatter.wordpress.com/).

Acknowledgements

The authors acknowledge funding from the USDA NIFA AFRI Water for Food Production Systems program, grant #2018-68011-28691 and funding from the National Science Foundation, grant #1739473.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2022. Title of presentation. Waste to Worth. Oregon, OH. April 18-22, 2022. URL of this page. Accessed on: today’s date.

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Manure Application Method and Timing Effects on Emission of Ammonia and Nitrous Oxide

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Abstract

We conducted a field study on corn to evaluate the effect of liquid dairy manure applied pre-plant (injection or surface broadcast with immediate or 3-day disk incorporation) or sidedressed at 6-leaf stage (injected or surface-applied) on emission of NH3 and N2O. Manure was applied at a rate of 6500 gal/acre, which supplied an average of 150 lb/acre of total N and 65 lb/acre of NH4-N. Ammonia emission was measured for 3 days after manure application using the dynamic chamber/equilibrium concentration technique, and N2O flux was quantified using the static chamber method at intervals of 3 to 14 days throughout the season. Ammonia-N losses were typically 30 to 50 lb/acre from pre-plant surface application, most of the loss occurring in the first 6 to 12 hours after application. Emission rates were reduced 60-80% by quick incorporation and over 90% by injection. Losses of N2O were relatively low (1 lb/acre or less annually), but pronounced peaks of N2O flux occurred from either pre-plant or sidedress injected manure in different years. Results show that NH3 emission from manure can be reduced substantially by injection or quick incorporation, but there may be some tradeoff with N2O flux from injection.

Why Study Land Application Emissions of Ammonia and Nitrous Oxide?
Figure 1. Injection equipment used for pre-plant application (top) and sidedress application (bottom) of liquid dairy manure.

Manure is a valuable source of nitrogen (N) for crop production, but gaseous losses of manure N as ammonia (NH3) and nitrous oxide (N2O) reduce the amount of N available to the crop and, therefore, its economic value as fertilizer. These N losses can also adversely affect air quality, contribute to eutrophication of surface waters via atmospheric deposition, and increase greenhouse gas emission. And the decreased available N in manure reduces the N:P ratio and can lead to a more rapid build-up of P in the soil for a given amount of available N. The most common approach to controlling NH3 volatilization from manure is to incorporate it into the soil with tillage or subsurface injection, which can reduce losses by 50 to over 90% compared to surface application (Jokela and Meisinger, 2008). Injecting into a growing corn crop at sidedress time offers another window of time for manure application (Ball-Coelho et al., 2006). While amounts of N lost as N2O are usually small compared to NH3, even low emissions can contribute to the greenhouse effect because N2O is about 300 times as potent as carbon dioxide in its effect on global warming (USEPA, 2010). We carried out a 4-year field experiment to evaluate the effect of dairy manure application method and timing and time of incorporation on a) corn yield, b) fertilizer N credits, c) ammonia losses, and) nitrous oxide emissions.

What Did We Do?
Figure 2. Average (2009-2011) NH3-N emission rates as affected by method and timing of manure application.

This field research was conducted at the Univ. of Wisconsin/USDA Agricultural Research Station in Marshfield, WI, on predominantly Withee silt loam (Aquic glossudalf), a somewhat poorly drained soil with 0 to 2% slope. Dairy manure was applied either at pre-plant (mid- to late May) or sidedress time (5-6-leaf stage). Pre-plant treatments were either injected with an S-tine injector (15-inch spacing; Fig. 1) or incorporated with a tandem disk immediately after manure application (< 1 hour), 1-day later, or 3 days later. All plots were chisel plowed 3 to 5 days after application. Sidedress manure applications were either injected with an S-tine injector (30-inch spacing) or surface applied (Fig. 1). Fertilizer N was applied to separate plots at pre-plant at rates of 0, 40, 80, 120, 160, and 200 lb/acre as urea and incorporated with a disk. Liquid dairy manure (average 14% solids) was applied at a target rate of 6,500 gal/acre. Manure supplied an average of 158 lb total N and 62 lb NH4-N per acre, but rates varied across years and application times.

Ammonia emission was measured following pre-plant and sidedress manure applications in 2009-2011 with the dynamic chamber/equilibrium concentration technique (Svensson, 1994). Measurement started immediately after manure application and continued through the third day. Ammonia measurement ended just before disking of the 3-day incorporation treatment, so the 3-day treatment represents surface-applied manure. Nitrous oxide was measured using the static, vented chamber technique following the GRACEnet protocol (Parkin and Venterea, 2010). Measurement began two days after pre-plant manure application and continued approximately weekly into October.

What Have We Learned?
Figure 3. Nitrous oxide (N2O) flux as affected by method and timing of dairy manure application from May to October of 2010 (A) and 2011 (B). Arrows show times of manure application. Note differences in scale for 2010 and 2011.

The 3-year average annual NH3 emission rate from surface applied (3-day incorporation) manure was relatively high immediately following application but declined rapidly after the first several hours to quite low levels (Fig. 2). Cumulative NH3-N loss over the full measurement period averaged over 40 lb/acre from surface application but was reduced by 75% with immediate disking and over 90% by injection. Ammonia losses varied somewhat by year, but patterns over time and reductions by incorporation were similar. The pattern of ammonia loss, 75% of the total loss in the first 6 to 12 hours, emphasizes the importance of prompt incorporation to reduce losses and conserve N for crop use.

Nitrous oxide flux was quite low for most manure treatments during most of the May to October period in both years (Fig. 3). However, there were some increases in N2O flux after manure application, and pronounced peaks of N2O emission from the injection treatment at either pre-plant (2010) or sidedress (2011) time. Greater emission from injection compared to other treatments may have occurred because injection of liquid manure places manure in a relatively concentrated band below the surface, creating anaerobic (lacking in oxygen) conditions. Nitrous oxide is produced by denitrification, a microbial process that is facilitated by anaerobic conditions. Reasons for the difference between 2010 and 2011 are not readily obvious, but are probably a result of different soil moisture and temperature conditions.
Figure 4. Annual (May-Oct.) loss of N2O as affected by method and timing of liquid dairy manure application. 2010 and 2011.

Based on these results, injection of liquid dairy manure resulted in opposite effects on NH3 and N2O emission, suggesting a trade-off between the two gaseous N loss pathways. However, the total annual N losses from N2O emissions (1 lb/acre or less; Fig. 4) were only a fraction of those from ammonia volatilization, so under the conditions of this study N2O emission is not an economically important loss. As noted earlier, however, N2O is a potent greenhouse gas, so even small amounts can contribute to the potential for global climate change. The dramatic reduction in NH3 loss from injection, though, may at least partially balance out the increased N2O because 1% of volatilized N is assumed to be converted to N2O (IPCC, 2010). Immediate disk incorporation was almost as effective as injection for controlling NH3 loss and, on average, resulted in less N2O emission than injection. But the separate field operation must be done promptly after manure application to be effective. A possible alternative is to use sweep injectors or other direct incorporation methods that place manure over a larger volume of soil and/or create more mixing with soil, thus creating conditions less conducive to denitrification and N2O loss.

Manure application timing and method/time to incorporation significantly affected grain yield in 2009, 2010, and 2012 and silage yield in 2012. Pre-plant injection produced greater yields than one or more of the broadcast treatments in 2009 (grain) and 2012 (grain and silage). Overall, yield effects of application and incorporation timing were variable from year to year, probably because of differences in weather and soil conditions and actual manure N rates applied. The fertilizer N equivalence of manure was calculated by comparing the yield achieved from each manure treatment to the yield response function from fertilizer N. Fertilizer N equivalence values were quite variable by year, but 4-year averages expressed as percent of total manure N applied were 52% for injection (pre-plant and sidedress), 37% for 1-hour or 1-day incorporation, and 34% for 3-day incorporation. So, when expressed as a percent of total manure N applied, N availability generally decreased as time to incorporation increased, which reflects the amounts of measured NH3 loss.

In summary, ammonia volatilization losses increased as the time to incorporation of manure increased. Injection of manure resulted in the lowest amount of NH3 volatilization, but higher N2O emissions. In this study, reducing the large NH3 losses by injecting manure provided more environmental benefit compared to the small increase in N2O emissions. In addition, injection or immediate incorporation resulted, on average, in higher fertilizer N value of manure for corn production. The decreased need for commercial fertilizer N could potentially result in greater profitability and a smaller carbon footprint.

Future Plans

We have started other research to evaluate yield response, N cycling, and emission of NH3 and N2O from various low-disturbance manure application methods in silage corn and perennial forage systems.

Authors

Bill Jokela, Research Soil Scientist, USDA-ARS, Dairy Forage Reserch Center, Marshfield, WI, bill.jokela@ars.usda.gov

Carrie Laboski, Assoc. Professor, Dept. of Soil Science, Univ. of Wisconsin

Todd Andraski, Researcher, Dept. of Soil Science, Univ. of Wisconsin

Additional Information

Acknowledgements

The authors gratefully acknowledge Matt Volenec and Ashley Braun for excellent technical assistance in conducting this research. Funding was provided, in part, by the USDA-Agricultural Research Service and the Wisconsin Corn Promotion Board.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2013. Title of presentation. Waste to Worth: Spreading Science and Solutions. Denver, CO. April 1-5, 2013. URL of this page. Accessed on: today’s date.

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