Vertical Stratification of Soil Phosphorus as a Concern for Dissolved Phosphorus Runoff in the Lake Erie Basin

Abstract

During the re-eutrophication of Lake Erie, dissolved reactive phosphorus (DRP) loading and concentrations to the lake have nearly doubled, while particulate phosphorus (PP) has remained relatively constant. One potential cause of increased DRP concentrations is P stratification, or the buildup of soil-test P (STP) in the upper soil layer (<5 cm). Stratification often accompanies no-till and mulch-till practices that reduce erosion and PP loading, practices that have been widely implemented throughout the Lake Erie Basin. To evaluate the extent of P stratification in the Sandusky Watershed, certified crop advisors were enlisted to collect stratified soil samples (0-5 or 0-2.5 cm) alongside their normal agronomic samples (0-20 cm) (n = 1758 fields). The mean STP level in the upper 2.5 cm was 55% higher than the mean of agronomic samples used for fertilizer recommendations. The amounts of stratification were highly variable and did not correlate with agronomic STPs (Spearman's r = 0.039, p = 0.178). Agronomic STP in 70% of the fields was within the buildup or maintenance ranges for corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] (0-46 mg kg −1 Mehlich-3 P). The cumulative risks for DRP runoff from the large number of fields in the buildup and maintenance ranges exceeded the risks from fields above those ranges. Reducing stratification by a one-time soil inversion has the potential for larger and quicker reductions in DRP runoff risk than practices related to drawing down agronomic STP levels. Periodic soil inversion and mixing, targeted by stratified STP data, should be considered a viable practice to reduce DRP loading to Lake Erie. Vertical Stratification of Soil Phosphorus as a Concern for Dissolved Phosphorus Runoff in the Lake Erie BasinDavid B. Baker,* Laura T. Johnson, Remegio B. Confesor, and John P. Crumrine T here is a long history of phosphorus (P) control programs in the Lake Erie Basin aimed at reducing cultural eutrophication. The first programs began in the 1970s and focused on controlling point sources (IJC, 1978), while the second focused on agricultural nonpoint sources, primarily through erosion control programs (IJC, 1983). The first was eminently successful in reducing total P (TP) loading from ~28,000 Mg yr −1 in 1968 to ~11,000 Mg yr −1 in 1981 (DePinto et al., 1986), while the second has fallen well short of its additional 2000-Mg yr −1 reduction target (OEPA, 2010; Baker et al., 2014a). In response to these P control programs, Lake Erie was viewed as a "poster child" for successful eutrophication control in the late 1980s and early 1990s (Matisoff and Ciborowski, 2005). Unfortunately, beginning in the late 1990s, the lake has undergone re-eutrophication such that the algal blooms of 2011 and 2015 were the largest and most widespread ever noted (Scavia et al., 2014;Stumpf et al., 2016).The re-eutrophication of Lake Erie corresponded temporally with the implementation of agricultural nonpoint-source controls that focused on the use of no-till and mulch-till practices to reduc...

Phosphorus and the Chesapeake Bay: Lingering Issues and Emerging Concerns for Agriculture

“…Although conservation tillage is widespread in the region (roughly two‐thirds of the Bay watershed's farm soils are in no‐till or some type of perennial forage), adoption of cover crops in Pennsylvania is not as extensive as in Maryland, where it has been heavily subsidized (13 vs. 29% of cropland area in Pennsylvania and Maryland, respectively, in 2017), and soil erosion remains a dominant concern of nutrient management specialists and resource conservation programs (Cela et al, 2016; Bryant, 2019). Even so, the emergence of dissolved P as a concern may also reflect the success of soil conservation programs, which struggle to deal with the persistent issue of vertical soil P stratification (Baker et al, 2017). …”

“…In cropped soils, P accumulation on the soil surface can occur very rapidly, with severe vertical stratification occurring even a few years after no‐till has been implemented (Baker et al, 2017). Phosphorus on or near the soil surface is generally the principal source of P in surface runoff and drainage water (Sharpley, 1985; Kleinman et al, 2015a,c).…”

The Latitudes, Attitudes, and Platitudes of Watershed Phosphorus Management in North America

“…However, since the early 2000s, there has been an increase in soluble P losses in the Western Lake Erie basin, linked to a “re‐eutrophication” of western Lake Erie and increases in the magnitude and frequency of nuisance and harmful algal blooms (Jarvie et al, 2017). While the exact reasons for this are still under investigation, there is likely a myriad of contributing factors (Smith et al, 2015b), including soil stratification, which, with continued broadcast application of P fertilizer, has resulted in accumulation of labile P at the soil surface (Baker et al, 2017), increases in hydrological connectivity via tile drainage, and reductions in suspended particulate matter available to sorb soluble P. It is increasingly clear that solutions to P‐related water quality problems from the 1980s and 1990s may have unintentionally contributed to a completely unexpected and different kind of P‐related water quality impairment (Jarvie et al, 2017). Indeed, mitigation efforts that are spatially precise are needed to effectively reduce P loads, and adaptive management is critical to success.…”

“…While cover crops perform exceptionally well at minimizing nitrate leaching and keeping the ground covered to minimize erosion (and associated sediment‐bound P; Angle et al, 1984; Zhu et al, 1989; Dabney et al, 2001), evidence in the literature indicates that this practice may exacerbate soluble P loss under some winter conditions (Bechmann et al, 2005; Tiessen et al, 2010; Cober et al, 2018). It is also possible that cover crops could exacerbate P stratification, which is one complicating factor in solving the soluble P conundrum (Baker et al, 2017). Further, reliance on a single practice such as cover crops does not directly guide producers to use P fertilizers judiciously, nor does it address legacy P that exists either in the field (i.e., high soil test P) or the P deposited beyond the edge of field that is in various stages of transit to the receiving water (i.e., sediments deposited in the floodplain or P spiraling through the stream network).…”

“…A better embrace of the complexity of the processes of P loss and understanding of trade‐offs in conservation strategies regarding P loss is needed to improve the relevance of programs to P mitigation (Kleinman et al, 2015). For example, soil health initiatives must come to terms with the consequence of severe vertical stratification of P in soils that can occur after several years of tillage exclusion (Baker et al, 2017; Smith et al, 2017). “Feed the soil to feed the plant” (Withers et al, 2014) is gradually being recognized as cost effective but inherently inefficient with regard to P use efficiency.…”