Peter J. A. Kleinman

Phosphorus legacy: overcoming the effects of past management practices to mitigate future water quality impairment

The water quality response to implementation of conservation measures across watersheds has been slower and smaller than expected. This has led many to question the efficacy of these measures and to call for stricter land and nutrient management strategies. In many cases, this limited response has been due to the legacies of past management activities, where sinks and stores of P along the land-freshwater continuum mask the effects of reductions in edge-of-field losses of P. Accounting for legacy P along this continuum is important to correctly apportion sources and to develop successful watershed remediation. In this study, we examined the drivers of legacy P at the watershed scale, specifically in relation to the physical cascades and biogeochemical spirals of P along the continuum from soils to rivers and lakes and via surface and subsurface flow pathways. Terrestrial P legacies encompass prior nutrient and land management activities that have built up soil P to levels that exceed crop requirements and modified the connectivity between terrestrial P sources and fluvial transport. River and lake P legacies encompass a range of processes that control retention and remobilization of P, and these are linked to water and sediment residence times. We provide case studies that highlight the major processes and varying timescales across which legacy P continues to contribute P to receiving waters and undermine restoration efforts, and we discuss how these P legacies could be managed in future conservation programs.

Phosphorus loss from land to water: integrating agricultural and environmental management

Phosphorus (P), an essential nutrient for crop and animal production, can accelerate freshwater eutrophication, now one of the most ubiquitous forms of water quality impairment in the developed world. Repeated outbreaks of harmful algal blooms (e.g., Cyanobacteria and Pfiesteria) have increased societys awareness of eutrophication, and the need for solutions. Agriculture is regarded as an important source of P in the environment. Specifically, the concentration of specialized farming systems has led to a transfer of P from areas of grain production to animal production. This has created regional surpluses in P inputs (mineral fertilizer and feed) over outputs (crop and animal produce), built up soil P in excess of crop needs, and increased the loss of P from land to water. Recent research has shown that this loss of P in both surface runoff and subsurface flow originates primarily from small areas within watersheds during a few storms. These areas occur where high soil P, or P application in mineral fertilizer or manure, coincide with high runoff or erosion potential. We argue that the overall goal of efforts to reduce P loss to water should involve balancing P inputs and outputs at farm and watershed levels by optimizing animal feed rations and land application of P as mineral fertilizer and manure. Also, conservation practices should be targeted to relatively small but critical watershed areas for P export.

The ecological sustainability of slash-and-burn agriculture

Abstract Slash-and-burn agroecosystems are important to rural poor and indigenous peoples in the developing world. Ecologically sound slash-and-burn agriculture is sustainable because it does not depend upon outside inputs based on fossil energy for fertilizers, pesticides and irrigation. One means of demonstrating the soundness of slash-and-burn agroecosystems is to prove empirically the ecological compatibility of this system of crop production. This paper examines the ecological sustainability of slash-and-burn agriculture based on the productivity of soil resources.

Managing agricultural phosphorus for water quality protection: principles for progress

BackgroundThe eutrophication of aquatic systems due to diffuse pollution of agricultural phosphorus (P) is a local, even regional, water quality problem that can be found world-wide.ScopeSustainable management of P requires prudent tempering of agronomic practices, recognizing that additional steps are often required to reduce the downstream impacts of most production systems.ConclusionsStrategies to mitigate diffuse losses of P must consider chronic (edaphic) and acute, temporary (fertilizer, manure, vegetation) sources. Even then, hydrology can readily convert modest sources into significant loads, including via subsurface pathways. Systemic drivers, particularly P surpluses that result in long-term over-application of P to soils, are the most recalcitrant causes of diffuse P loss. Even in systems where P application is in balance with withdrawal, diffuse pollution can be exacerbated by management systems that promote accumulation of P within the effective layer of effective interaction between soils and runoff water. Indeed, conventional conservation practices aimed at controlling soil erosion must be evaluated in light of their ability to exacerbate dissolved P pollution. Understanding the opportunities and limitations of P management strategies is essential to ensure that water quality expectations are realistic and that our beneficial management practices are both efficient and effective.

Phosphorus transport in agricultural subsurface drainage: a review.

Phosphorus (P) loss from agricultural fields and watersheds has been an important water quality issue for decades because of the critical role P plays in eutrophication. Historically, most research has focused on P losses by surface runoff and erosion because subsurface P losses were often deemed to be negligible. Perceptions of subsurface P transport, however, have evolved, and considerable work has been conducted to better understand the magnitude and importance of subsurface P transport and to identify practices and treatments that decrease subsurface P loads to surface waters. The objectives of this paper were (i) to critically review research on P transport in subsurface drainage, (ii) to determine factors that control P losses, and (iii) to identify gaps in the current scientific understanding of the role of subsurface drainage in P transport. Factors that affect subsurface P transport are discussed within the framework of intensively drained agricultural settings. These factors include soil characteristics (e.g., preferential flow, P sorption capacity, and redox conditions), drainage design (e.g., tile spacing, tile depth, and the installation of surface inlets), prevailing conditions and management (e.g., soil-test P levels, tillage, cropping system, and the source, rate, placement, and timing of P application), and hydrologic and climatic variables (e.g., baseflow, event flow, and seasonal differences). Structural, treatment, and management approaches to mitigate subsurface P transport-such as practices that disconnect flow pathways between surface soils and tile drains, drainage water management, in-stream or end-of-tile treatments, and ditch design and management-are also discussed. The review concludes by identifying gaps in the current understanding of P transport in subsurface drains and suggesting areas where future research is needed.

Phosphorus loss from an agricultural watershed as a function of storm size.

Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1-3, 3-5, 5-10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha(-1) yr(-1)) and 80% of total P (TP) exported (515 g ha(-1) yr(-1)). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m(3) ha(-1); 63%) and export of DP (574 g ha(-1); 54%) and TP (2423 g ha(-1); 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09-0.16 mg L(-1)) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.

Water Quality Remediation Faces Unprecedented Challenges from “Legacy Phosphorus”

“Legacy Phosphorus” Helen P. Jarvie,†,* Andrew N. Sharpley,‡ Bryan Spears, Anthony R. Buda, Linda May, and Peter J. A. Kleinman †Centre for Ecology and Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, U.K. ‡Department of Crop, Soil and Environmental Sciences, Division of Agriculture, University of Arkansas, Fayetteville, Arkansas, United States Centre for Ecology and Hydrology, Bush Estate, Penicuik, Midlothian, U.K. Agricultural Research Service, Pasture Systems and Watershed Management Research Unit, U.S. Department of Agriculture, University Park, Pennsylvania, United States

Environmental and Economic Impacts of Reducing U.S. Agricultural Pesticide Use

Several studies suggest that it is technologically feasible to reduce pesticide use in the United States 35—50% without reducing crop yields (PSAC, 1965; OTA, 1979; NAS, 1989; Palladino, 1989). Two recent events in Denmark and Sweden support these assessments. Denmark developed an action plan in 1985 to reduce the use of pesticides 50% before 1997 (Mogensen, 1989). Sweden also approved a program in 1988 to reduce pesticide use by 50% within 5 years (NBA, 1988). The Netherlands is developing a program to reduce pesticide use 50% in 10 years (Suddeutsche Zeitung, 1989). These proposals, along with Huffaker’s (1980) assessment that the United States overuses pesticides, prompted us to investigate the feasibility of reducing the annual use of synthetic organic pesticides by approximately one-half.

Estimating soil phosphorus sorption saturation from Mehlich-3 data

Soil phosphorus sorption saturation (Psat) measures the degree to which soil phosphorus (P) sorption sites have been filled and has been found to be a good indicator of P availability to runoff and leachate. At present, analytical methods required to estimate Psat are generally not offered by soil testing laboratories. This study evaluated the use of Mehlich-3 data in estimating Psat in a wide range of soils. In acidic soils Psat estimated from Mehlich-3 P, iron (Fe), and aluminum (Al) was highly correlated with Psat estimated from ammonium oxalate data as well as with a reference Psat estimated from bicarbonate P and the Langmuir sorption maximum In alkaline soils Psat estimated with Mehlich-3 P and calcium (Ca) was highly correlated with the reference Psat and the strength of that correlation improved only slightly by factoring in soil clay content Results indicate that Psat may be effectively estimated from Mehlich-3 data across a wide range of soils. This study confirms that Psat may be readily estimated by soil testing laboratories that routinely measure Mehlich-3 P, Al, Fe, and Ca.

Evaluating the Success of Phosphorus Management from Field to Watershed

Studies have demonstrated some P loss reduction following implementation of remedial strategies at field scales. However, there has been little coordinated evaluation of best management practices (BMPs) on a watershed scale to show where, when, and which work most effectively. Thus, it is still difficult to answer with a degree of certainty, critical questions such as, how long before we see a response and where would we expect to observe the greatest or least response? In cases where field and watershed scales are monitored, it is not uncommon for trends in P loss to be disconnected. We review case studies demonstrating that potential causes of the disconnect varies, from competing sources of P at watershed scales that are not reflected in field monitoring to an abundance of sinks at watershed scales that buffer field sources. To be successful, P-based mitigation strategies need to occur iteratively, involve stakeholder driven programs, and address the inherent complexity of all P sources within watersheds.