The effect of alfalfa on subsurface nutrient losses across different storm event types

Authors: ARRUETA, LOURDES - University Of Wisconsin; King, Kevin; HANRAHAN, BRITTANY - Us Geological Survey (USGS); MARTIN, JAY - The Ohio State University; QUIRING, STEVEN - The Ohio State University; KALCIC, MARGARET - University Of Wisconsin

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reducing phosphorus transport in the Western Lake Erie Basin watershed continues be a focal point for addressing the re-eutrophication of Lake Erie and the occurrence of harmful algal blooms, particularly that transport in subsurface tile drainage. Under projected climate change scenarios, more phosphorus transport is expected due to larger rainfall events. Introducing perennial crops, such as alfalfa, was shown to reduce tile drainage phosphorus losses from larger rainfall events measured at two different fields in north western Ohio. These findings are important for informing conservation efforts and prioritizing conservation practices within the watershed.

Technical Abstract: This study examines the effect of alfalfa (Medicago sativa L.) on subsurface nitrogen and phosphorus loads across storm event types using edge-of-field monitoring data from two sites (A and B) located in the Northwest region of Ohio, USA. A k-median cluster analysis was employed to classify 462 storm events at Site A, and 684 storm events at Site B based on precipitation amount and wet antecedent moisture conditions (AMC). Subsequently, patterns of nutrient loss in tile drainage were compared between fields with alfalfa and fields without alfalfa using a difference-in-differences analysis across three identified storm event types: Moderate-dry storm events (precipitation amount<34 mm, and wet AMC<27 mm), moderate-wet storm events (precipitation amount<39 mm, and wet AMC>27 mm), and large storm events (precipitation amount>34 mm). Results indicated that alfalfa reduced subsurface discharge during large storm events at site B, while no significant differences were observed at Site A. Moreover, alfalfa reduced subsurface nitrate and total nitrogen loads compared to a corn/wheat rotation across all storm event types at Site A, while no significant differences were observed at Site B. Furthermore, at both sites, alfalfa reduced subsurface dissolved reactive phosphorus and total phosphorus loads during large events compared to the fields with annual crops. The impact of alfalfa on nutrient loads during large storm events is important, as most nutrient exports occur during these events.