Contrasting the influence of crop rotation on phosphorus balances and losses in agricultural fields across a tile-drained landscape in Ohio, USA

Authors: Hanrahan, Brittany; King, Kevin; Rumora, Kathryne - Katie; Stinner, Jedediah

Submitted to: Journal of Great Lakes Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2023
Publication Date: 9/16/2023
Citation: Hanrahan, B.R., King, K.W., Rumora, K.R., Stinner, J.H. 2023. Contrasting the influence of crop rotation on phosphorus balances and losses in agricultural fields across a tile-drained landscape in Ohio, USA. Journal of Great Lakes Research. 49(6). Article 102232. https://doi.org/10.1016/j.jglr.2023.09.003.
DOI: https://doi.org/10.1016/j.jglr.2023.09.003

Interpretive Summary: Fertilizer nutrients, such as nitrogen (N) and phosphorus (P), that are applied to agricultural fields in excess of crop needs can accumulate in the soil profile. These accumulated nutrients can then be leached to adjacent streams where they are subsequently transported to downstream waters, such as the Laurentian Great Lakes or the Gulf of Mexico. Therefore, reducing N and P losses from agricultural fields with conservation or best management practices may improve local and downstream water quality. One such practice is conservation crop rotation, or the planting of a series of crops in the same field over a given period of time. Conservation crop rotation has the potential to reduce overall nutrient inputs (by including crops that have lower N and P requirements) and increase nutrient demand (by increasing biodiversity, vegetative land cover, and the length of the growing season). In this study, we calculated P balances (Inputs – Outputs) in agricultural fields with corn-soybean rotations (CS) and fields with corn-soybean-wheat rotations (CSW) to compare patterns of nutrient accumulation or depletion. We also compared losses of dissolved reactive P (DRP) and total P (TP) between the CS and CSW rotations. We found that annual P balances were generally negative, indicating annual P deficits in CS and CSW fields. However, DRP and TP losses were significantly greater from CSW fields compared to CS fields, likely because soil test phosphorus (STP) concentrations were greater in CSW fields as a result of past and current organic fertilizer (i.e., manure) application. The fraction of applied P exported from fields as both DRP and TP was also greater in CSW compared to CS, further confirming more available P susceptible to loss. While this work indicates no significant benefit of conservation crop rotation, our study shows that additional research between conventional and conservation crop rotations on fields with similar soil test phosphorus concentrations is warranted prior to any definitive conclusions. Findings here also confirm and emphasize P application in accordance with fertility recommendations.

Technical Abstract: Excess phosphorus (P) applied to agricultural fields accumulates in the soil profile and is susceptible to leaching, subsequently impacting adjacent and downstream aquatic ecosystems. Planting a series of crops in the same field over a given period of time is referred to as conservation crop rotation, which has the potential to reduce nutrient losses from agricultural systems by reducing overall nutrient inputs (i.e., including crops that have lower N or P requirements) and increasing nutrient retention or demand (i.e., by increasing biodiversity, vegetative land cover, and length of the growing season). In this study, we calculated P balances (Inputs – Outputs) in agricultural fields with corn-soybean rotations (CS) and fields with corn-soybean-wheat rotations (CSW) to compare patterns of nutrient accumulation or depletion. We also compared losses of dissolved reactive P (DRP) and total P (TP) between the CS and CSW rotations. Results here indicated that annual P balances were generally negative, indicating annual P deficits in both CS (median = -9 kg P ha-1) and CSW (median = -5 kg P ha-1) fields. However, DRP and TP losses were significantly greater from CSW fields (median = 0.5 kg DRP ha-1 and 2 kg TP ha-1) compared to CS fields (median = 0.1 kg DRP ha-1 and 1 kg TP ha-1), likely due to larger pools of P in CSW fields from current and historical fertilizer management practices. The fraction of applied P exported from fields as both DRP and TP was also greater in CSW (2% as DRP and 9% as TP) compared to CS (1% as DRP and 3% as TP), further confirming more available P susceptible to loss. While findings here indicate no significant benefit of conservation crop rotation, additional research between conventional and conservation crop rotations on fields with similar soil test phosphorus concentrations is warranted prior to any definitive conclusions. These findings also confirm and emphasize P application in accordance with fertility recommendations.