Soil controls of phosphorus in runoff: Management barriers and opportunities

Abstract

Kleinman, P. J. A., Sharpley, A. N., Budda, A. R., McDowell, R. W. and Allen, A. L. 2011. Soil controls of phosphorus in runoff: Management barriers and opportunities. Can. J. Soil Sci. 91: 329–338. The persistent problem of eutrophication, the biological enrichment of surface waters, has produced a vast literature on soil phosphorus (P) effects on runoff water quality. This paper considers the mechanisms controlling soil P transfers from agricultural soils to runoff waters, and the management of these transfers. Historical emphases on soil conservation and control of sediment delivery to surface waters have demonstrated that comprehensive strategies to mitigate sediment-bound P transfer can produce long-term water quality improvements at a watershed scale. Less responsive are dissolved P releases from soils that have historically received P applications in excess of crop requirements. While halting further P applications to such soils may prevent dissolved P losses from growing, the desorption of P from soils that is derived from historical inputs, termed here as “legacy P”, can persist for long periods of time. Articulating the role of legacy P in delaying the response of watersheds to remedial programs requires more work, delivering the difficult message that yesterday's sinks of P may be today's sources. Even legacy sources of P that occur in low concentration relative to agronomic requirement can support significant loads of P in runoff under the right hydrologic conditions. Strategies that take advantage of the capacity of soils to buffer dissolved P losses, such as periodic tillage to diminish severe vertical stratification of P in no-till soils, offer short-term solutions to mitigating P losses. In some cases, more aggressive strategies are required to mitigate both short-term and legacy P losses.

Assessing edge-of-field nutrient runoff from agricultural lands in the United States: How clean is clean enough?

“…For example, soils with high soil test P may take more than 14 years to return to optimum agronomic P levels even with no further P application (McCollum 1991;Kleinman et al 2011;Svanbäck et al 2015); therefore, they remain a source transferring P to surface waters over long periods of time, reducing the immediate impacts of P loss reduction strategies (Maguire et al 2009). …”

Convergence of agricultural intensification and climate change in the Midwestern United States: implications for soil and water conservation

“…Stream nutrient loads have been repeatedly tied to increased fertiliser applications and broad-based agriculture being practiced across the landscape. Nutrient transport mechanisms are dominated by leaching and subsurface tile drainage of water, carrying nitrate-N (Jaynes et al 2001;Singer et al 2011) and dissolved phosphorus (Jacobson et al 2011), and surface runoff carrying sediment enriched with phosphorus (Kleinman et al 2011). The combined effect of artificial drainage, wetland loss, and agricultural nutrients on Midwest aquatic ecosystems was recently reviewed by Blann et al (2009).…”

An assessment of vegetation characteristics and hydrologic flow pathways on the effectiveness of vegetated buffer strips for phosphorus reduction in an agricultural watershed

“…Due to the selective transport during runoff events of clay-sized particles and organic material to which P easily binds, a large portion of P removed from a watershed is often in the particulate form (Kleinman, Sharpley, Buda, McDowell, & Allen, 2011;Sharpley, Kleinman, McDowell, Gitau, & Bryant, 2002). However, northern climates behave differently with regards to the generation of overland runoff because runoff is more frequently driven by the snowmelt in the spring rather than precipitation events throughout the rest of the year.…”

“…One explanation for this lack of improvement in water quality is the concept of 'legacy phosphorus,' where P from past land management strategies has accumulated in soils and water bodies and is being remobilized, even as current agricultural practices are reducing P use (Kleinman et al, 2011;McDowell, Sharpley, & Chalmers, 2002). Elser and Bennett (2011) argue that the low nutrient use efficiency of crops coupled with the heavy application of fertilizers have fundamentally disrupted the P (and nitrogen) cycles as the normal biological controls of the ecosystem are overwhelmed and fail to function.…”

“…Coined 'legacy P' -P that has accumulated in soils over years but that can be remobilized and transported to surface and groundwater -this source of P has recently been an increasing focus for studies on various BMP strategies (Kleinman et al, 2011). Additional research has…”