Environmental and Agronomic Evaluation of Struvite in Rice Production Systems

Furrow-irrigation constitutes an alternative water regime that has been increasingly adopted in Arkansas. Among the management of nutrients in furrow-irrigated systems, phosphorus (P) represents a substantial challenge. The environmental sustainability of rice (Oryza sativa) production systems needs to be evaluated across different water regimes and fertilizer-P sources. Therefore, the objectives of the following studies were to: i) evaluate season-long carbon dioxide (CO2) and methane (CH4) emissions and global warming potential (GWP) under different tillage treatments [i.e., conventional tillage (CT) and no-tillage (NT)] and at different site positions (i.e., up-, mid-, down-slope) along the predominant slope of a production-scale, furrow-irrigated rice field in east-central Arkansas throughout the 2018 and 2019 growing seasons, ii) evaluate the environmental impact of electrochemically precipitated struvite (ECST) compared to other commonly used, commercially available fertilizer-P sources [i.e., triple superphosphate (TSP) and diammonium phosphate (DAP)], a commercially available chemically precipitated struvite (CPST), and an unamended control on season-long CO2, CH4, and nitrous oxide (N2O) emissions and GWP on rice grown under flooded conditions in the greenhouse in 2020 and 2021, iii) evaluate the effects of water regime (i.e., flooded and furrow-irrigated conditions) and fertilizer-P source [i.e., DAP, CPST, ECST, TSP, and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in the greenhouse in 2021, and iv) evaluate the effects of fertilizer source [i.e., ECST, CPST, TSP, DAP, environmentally smart nitrogen (ESN), and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in a furrow-irrigated rice field in east-central Arkansas in 2022. Gas samples were collected weekly in each growing season between planting and harvest using the enclosed-headspace, static-chamber approach. For Objective 1, in 2018, season-long CO2 (25391 kg CO2 ha-1) and CH4 (64.0 kg CH4 ha-1) emissions and estimated GWP (36396 CO2 eq.) were greater from the down- than the up- and mid-slope positions; in 2019, season-long CH4 emissions (85.0 kg CH4 ha-1) were greatest from the down-slope position, while CO2 (23496 kg CO2 ha-1) emissions were greatest from the down-slope/CT combination. For Objective 2, in both years, ECST had the numerically lowest GWP (7.41 and 7.61 Mg CO2 eq. ha-1 season-1 in 2020 and 2021, respectively). For Objective 3, mean season-long CH4 emissions were 10 times greater (P \u3c 0.05) under flooded (29.4 kg CH4 ha-1 season-1) than under furrow-irrigated conditions (2.9 kg CH4 ha-1 season-1) and four times lower (P \u3c 0.05) with ECST (3.4 kg CH4 ha-1 season-1) than other fertilizer-P sources, while mean GWP under furrow-irrigated conditions was almost 40% lower (P \u3c 0.05) than under flooded conditions. For Objective 4, N2O emissions were lowest (P \u3c 0.05) from ESN (1.50 kg ha-1 season-1), which did not differ from TSP, CPST, ECST, and DAP. Global warming potential was also lowest (P \u3c 0.05) from ESN (1612 kg CO2 eq. ha-1 season-1), which did not differ from TSP, ECST, CPST, and DAP. Slow-release fertilizers, such as ECST, could be an effective mitigation tool to reduce GHG emissions from furrow-irrigated rice

Correlation Analyses among Soil, Plant, and Environmental Variables and Greenhouse Gas Emissions from Furrow-irrigated Rice on a Silt-loam Soil

Alternative water management practices for rice (Oryza sativa) production have been developed for water conservation purposes, such as the relatively new furrow-irrigated rice production system, which results in spatially variable volumetric water content (VWC), temperature, and oxidation-reduction (redox) potential. No research has been conducted to relate greenhouse gas (GHG) production to soil and plant properties or environmental factors under furrow-irrigated rice. The objective of this field study was to evaluate correlations between methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) fluxes and emissions and global warming potential (GWP) and near-surface soil properties and environmental factors over two growing seasons (2018 and 2019) under furrow-irrigated rice on a silt-loam soil in eastern Arkansas. Gas samples were collected weekly between planting and harvest from enclosed-headspace, static chambers and analyzed by gas chromatography. Methane fluxes were correlated (P \u3c 0.01) with VWC (r = 0.18) and soil redox potential (r = -0.59), N2O fluxes were correlated (P \u3c 0.01) with soil redox potential (r = 0.13), and CO2 fluxes were correlated (P \u3c 0.05) with VWC (r = 0.29), soil redox potential (r = -0.27) and soil temperature (r = 0.09). Methane and N2O emissions were positively (0.36 \u3c r \u3c 0.78) and negatively (-0.33 \u3c r \u3c -0.54) correlated (P \u3c 0.01) with numerous soil and plant properties. Significant multiple regression models predicting season-long CH4-C, N2O-N, CO2-C, and GWP from a suite of soil and plant properties were identified (0.49 \u3c R2 \u3c 0.78). Results of this study demonstrated numerous soil, plant, and environmental factors substantially control GHG production and release, which can be used to mitigate GHG emissions from the furrow-irrigated rice production system to improve current and future sustainability of rice production in the United States

Rice Biomass Response to Various Phosphorus Fertilizers in a Phosphorus-Deficient Soil Under Simulated Furrow-Irrigation

Wastewater-recovered phosphorus (P), in the form of the mineral struvite (MgNH4PO4∙6H2O), may provide a sustainable alternative to decreasing rock-phosphate reserves. Struvite can be generated via precipitation methods, potentially reducing the amount of P runoff to aquatic ecosystems. The objective of this greenhouse tub study was to evaluate the effects of chemically and electrochemically precipitated struvite (CPST and ECST, respectively) on aboveground plant response in a hybrid rice cultivar grown using furrow-irrigation compared to other common fertilizer-P sources [i.e., triple super phosphate (TSP) and diammonium phosphate (DAP)] using three replications of fertilizer treatment in a P-deficient silt loam (Typic Glossaqualfs). Aboveground rice dry matter (DM), aboveground DM P uptake, grain yield, and grain P uptake from CPST and ECST did not differ from DAP or TSP. However, aboveground DM P concentration was numerically largest (P \u3c 0.05) from TSP (0.05 %), which did not differ from DAP, and was at least 2.5 times larger than that from ECST, CPST, and the unamended control (UC). Similar rice responses among struvite and other common fertilizer-P sources suggest CPST and ECST are both possible alternative fertilizer-P sources that warrant further research into struvite’s role in food production and water quality restoration and preservation

Rice Biomass Response to Various Phosphorus Fertilizers in a Phosphorus-Deficient Soil Under Simulated Furrow-Irrigation

Wastewater-recovered phosphorus (P), in the form of the mineral struvite (MgNH4PO4∙6H2O), may provide a sustainable alternative to decreasing rock-phosphate reserves. Struvite can be generated via precipitation methods, potentially reducing the amount of P runoff to aquatic ecosystems. The objective of this greenhouse tub study was to evaluate the effects of chemically and electrochemically precipitated struvite (CPST and ECST, respectively) on aboveground plant response in a hybrid rice cultivar grown using furrow-irrigation compared to other common fertilizer-P sources [i.e., triple super phosphate (TSP) and diammonium phosphate (DAP)] using three replications of fertilizer treatment in a P-deficient silt loam (Typic Glossaqualfs). Aboveground rice dry matter (DM), aboveground DM P uptake, grain yield, and grain P uptake from CPST and ECST did not differ from DAP or TSP. However, aboveground DM P concentration was numerically largest (P \u3c 0.05) from TSP (0.05 %), which did not differ from DAP, and was at least 2.5 times larger than that from ECST, CPST, and the unamended control (UC). Similar rice responses among struvite and other common fertilizer-P sources suggest CPST and ECST are both possible alternative fertilizer-P sources that warrant further research into struvite’s role in food production and water quality restoration and preservation

Environmental and Agronomic Evaluation of Struvite in Rice Production Systems

Furrow-irrigation constitutes an alternative water regime that has been increasingly adopted in Arkansas. Among the management of nutrients in furrow-irrigated systems, phosphorus (P) represents a substantial challenge. The environmental sustainability of rice (Oryza sativa) production systems needs to be evaluated across different water regimes and fertilizer-P sources. Therefore, the objectives of the following studies were to: i) evaluate season-long carbon dioxide (CO2) and methane (CH4) emissions and global warming potential (GWP) under different tillage treatments [i.e., conventional tillage (CT) and no-tillage (NT)] and at different site positions (i.e., up-, mid-, down-slope) along the predominant slope of a production-scale, furrow-irrigated rice field in east-central Arkansas throughout the 2018 and 2019 growing seasons, ii) evaluate the environmental impact of electrochemically precipitated struvite (ECST) compared to other commonly used, commercially available fertilizer-P sources [i.e., triple superphosphate (TSP) and diammonium phosphate (DAP)], a commercially available chemically precipitated struvite (CPST), and an unamended control on season-long CO2, CH4, and nitrous oxide (N2O) emissions and GWP on rice grown under flooded conditions in the greenhouse in 2020 and 2021, iii) evaluate the effects of water regime (i.e., flooded and furrow-irrigated conditions) and fertilizer-P source [i.e., DAP, CPST, ECST, TSP, and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in the greenhouse in 2021, and iv) evaluate the effects of fertilizer source [i.e., ECST, CPST, TSP, DAP, environmentally smart nitrogen (ESN), and an unamended control] on season-long CO2, CH4, and N2O emissions and GWP in a furrow-irrigated rice field in east-central Arkansas in 2022. Gas samples were collected weekly in each growing season between planting and harvest using the enclosed-headspace, static-chamber approach. For Objective 1, in 2018, season-long CO2 (25391 kg CO2 ha-1) and CH4 (64.0 kg CH4 ha-1) emissions and estimated GWP (36396 CO2 eq.) were greater from the down- than the up- and mid-slope positions; in 2019, season-long CH4 emissions (85.0 kg CH4 ha-1) were greatest from the down-slope position, while CO2 (23496 kg CO2 ha-1) emissions were greatest from the down-slope/CT combination. For Objective 2, in both years, ECST had the numerically lowest GWP (7.41 and 7.61 Mg CO2 eq. ha-1 season-1 in 2020 and 2021, respectively). For Objective 3, mean season-long CH4 emissions were 10 times greater (P \u3c 0.05) under flooded (29.4 kg CH4 ha-1 season-1) than under furrow-irrigated conditions (2.9 kg CH4 ha-1 season-1) and four times lower (P \u3c 0.05) with ECST (3.4 kg CH4 ha-1 season-1) than other fertilizer-P sources, while mean GWP under furrow-irrigated conditions was almost 40% lower (P \u3c 0.05) than under flooded conditions. For Objective 4, N2O emissions were lowest (P \u3c 0.05) from ESN (1.50 kg ha-1 season-1), which did not differ from TSP, CPST, ECST, and DAP. Global warming potential was also lowest (P \u3c 0.05) from ESN (1612 kg CO2 eq. ha-1 season-1), which did not differ from TSP, ECST, CPST, and DAP. Slow-release fertilizers, such as ECST, could be an effective mitigation tool to reduce GHG emissions from furrow-irrigated rice

Water regime and fertilizer‐phosphorus source effects on greenhouse gas emissions from rice

Abstract Greenhouse gas (GHG) emissions from rice (Oryza sativa) systems have been correlated to water management practice, but to date, no study has directly evaluated three main GHGs (i.e., methane [CH4], nitrous oxide [N2O], and carbon dioxide [CO2]) under flood‐ and furrow‐irrigated conditions at the same time as affected by various fertilizer‐phosphorus (P) sources, in particular the reportedly slow‐release struvite‐P source. Therefore, the objective of this study was to evaluate the effect of water regime (flooded and furrow‐irrigated) and fertilizer‐P source (diammonium phosphate, chemically precipitated struvite, electrochemically precipitated struvite [ECST], triple superphosphate, and an unamended control) on GHG emissions and two‐ and three‐gas global warming potentials (GWP* and GWP, respectively) in the greenhouse. Methane emissions were 10 times greater (p < 0.05) under flooded (29.4 kg CH4 ha−1 season−1) than under furrow‐irrigated conditions (2.9 kg CH4 ha−1 season−1), and four times lower (p < 0.05) with ECST (3.4 kg CH4 ha−1 season−1) than other fertilizer‐P sources, while CO2 emissions were three times greater (p < 0.05) under furrow‐irrigated (23,428 kg CO2 ha−1 season−1) than under flooded (8290 kg CO2 ha−1 season−1) conditions. The GWP* under furrow‐irrigated conditions was almost 40% lower (p < 0.05) than under flooded conditions. Although N2O emissions were unaffected by fertilizer‐P source, the N2O contribution to GWP* was more than 80% under furrow‐irrigated conditions. Flood‐ and furrow‐irrigated water regimes require diversified approaches in GHG mitigation, where the best management for ECST needs to be more fully evaluated