As field conditions progress toward being suitable for planting, spring also brings a period of seasonally high precipitation and subsequent flow from tile drainage and surface runoff. In fact, a recent analysis of rainfall patterns from 1975-2017 over the Western Lake Erie Basin (WLEB) showed increasing rainfall amounts and event intensity lead to more water leaving the field per unit of precipitation. As a result, concerns of soil and phosphorus (P) loss in many areas becomes heightened during this time of the year.
The origins of P that may impair water quality varies by physiographic region, watershed, and field. Using 4R Nutrient Stewardship principles of the right source, rate, time, and place reduces losses of recently applied P; however, legacy P losses (P that does not come from recent applications) has been well-documented in soils and sediments. How much P is lost from the legacy pool is a question that many experts are trying to answer.
Recent work from the ARS Soil Drainage Research team (Columbus, OH) has shed some light onto critical relationships between legacy P in soil, tile drainage, and surface runoff. Scientists William Osterholz, Brittany Hanrahan, and Kevin King conducted an edge-of-field study on 39 fields in northwest Ohio from 2011 to 2018. Findings showed a strong relationship between elevated total and dissolved reactive P losses with larger legacy soil test P (figure 2). The authors pointed to a few other important insights from this study:
- The size of the legacy soil P pool did not influence behavior of tillage drainage or surface runoff
- Disrupting the flow path of surface P to macropores and tile lines could mitigate legacy P issues
- Greater tile flow was associated with greater soil-bound and total P losses, particularly in fine-textured soils.
These insights emphasize the importance of a frequent, comprehensive soil sampling program to accurately assess not only agronomic P needs, but susceptibility to losses as well.
Figure 2. from Osterholz et al. (2020) Shows the relationship of dissolved-reactive P concentration and soil test P for tile drainage (A) and surface runoff (B).
The recently accepted article in the Journal of Environmental Quality can be found here under the following citation:
Osterholz, W. R., Hanrahan, B. R., & King, K. W. Legacy phosphorus concentration‐discharge relationships in surface runoff and tile drainage from Ohio crop fields. Journal of Environmental Quality. doi:10.1002/jeq2.20070