Summary prepared by: William Osterholz, USDA-ARS Soil Drainage Research Unit, Columbus, Ohio, USA
Osterholz, W., Simpson, Z., Williams, M., Shedekar, V., Penn, C., & King, K. (2024). New phosphorus losses via tile drainage depend on fertilizer form, placement, and timing. Journal of Environmental Quality 53, 241-252. https://doi.org/10.1002/jeq2.20549
Major Findings:
We analyzed P loss data from tile drainage systems in Ohio and Indiana to estimate the newly applied P lost from >150 P fertilizer or manure applications. The analysis showed:
- Recently applied fertilizers (new P) typically contributed minimally to tile drainage P losses.
- Old soil P was the dominant source of P losses through tile drainage systems.
- The amount of new P lost was small (typically <1%) relative to the amount applied.
- Surface placement, manure, and late fall timing enhanced the risk of new P losses.
Tile drain DRP losses primarily came from old P sources like legacy soil P (shown by the gray portion of each bar) with a smaller amount derived from newly applied P fertilizer or manure (black portion of each bar). Data is from 38 fields in Ohio and Indiana, with fields ordered according to percentage of DRP loss from new P sources.
Contributions to the conservation drainage community
Tile drainage is an important pathway for agricultural P losses in Ohio and Indiana, but little is known about the relative importance of newly applied P fertilizers and old soil P (aka legacy P) to tile drainage losses. Understanding these sources could help direct efforts to reduce P loss, for instance 4R fertilizer management practices will primarily reduce new P losses, while old P losses may require edge-of-field practices and/or drawdown of soil P.
Researchers at USDA-ARS and Ohio State University analyzed edge-of-field P losses from tile drains in 38 fields in Ohio and Indiana. Using a statistical model they estimated expected P losses from old P sources, and compared those with the actual losses following P applications. This enabled calculation of the amount of P that was rapidly lost from new P applications. When researchers compared the magnitudes of P lost from new and old P sources, they observed that new P losses accounted for <15% of the overall P lost from these tile drains, meaning that old P was the dominant source. The results emphasized the importance of addressing the old P source for achieving meaningful P loss reductions in tile drainage.
Additionally, on average across >150 fertilizer and manure applications, the amount of new P lost was typically less than 1% of the amount applied. Regarding fertilizer management strategies, broadcast applications of fertilizer or manure posed a greater risk for large new P losses than applications that were placed below the surface. Additionally, manure had a greater risk of new P loss than commercial P fertilizer, and several of the late fall manure applications were associated with the greatest new P losses. Therefore, mitigation of new P losses through tile drainage should focus on reducing surface P applications, particularly of manure in late fall.