Peter J. A. Kleinman

Phosphorus index (P‐index) was developed to assess field vulnerability to phosphorus (P) loss and guide P management decisions. The original structure of the P‐index was additive, and with continued refinement, multiplicative and component‐based indices were developed. Alabama adopted the additive version in early 2000; however, the tool was never tested for its performance. The objectives of this study were to (i) evaluate the Alabama P‐index using edge‐of‐field P loss data, (ii) test if multiplicative (Tennessee) and component‐based (Georgia) P‐indices perform better, and (iii) improve and test the performance of a modified Alabama P‐index. We evaluated the performance by examining the strength and directional relationship between P‐index scores and annual P loads. The Alabama P‐index showed weak correlations ( r < 0.50) between risk scores and measured dissolved reactive phosphorus (DRP), total particulate phosphorus (TPP), and total phosphorus (TP) loads. Additionally, directional inaccuracies were observed, indicating that the index misclassified the relative risk of P loss. Further, we evaluated multiplicative and component‐based indices but found similar discrepancies between predicted risk scores and actual P loading. Subsequently, we modified the Alabama P‐index by replacing soil test P with the phosphorus saturation ratio and substituting the underground outlet system factor with the timing of P application. Minor adjustments to weighting factors were made. The modified P‐index demonstrated statistically significant correlations ( r > 0.51) and directional alignment with DRP, TPP, and TP loads, suggesting it can serve as a reliable interim tool for assessing P losses. Future research should focus on restructuring and validating a component‐based P‐index tailored to Alabama's agricultural systems.

The pace of global change complicates the assessment of the outcomes of agricultural management, hindering decision‐making by producers, researchers, and consumers. The Long‐Term Agroecosystem Research Network (LTAR) is in a unique position to advance monitoring to inform decision‐making. Here, we describe how the network selected performance indicators designed to measure the trade‐offs from various farming and ranching approaches. Indicator selection was motivated by the need for common indicators that apply to the diversity of LTAR sites, but they are intended for widespread use by producers and other managers via the Agricultural Performance Indicator and Context Knowledge System (AgPICKS). An initial set of domains, attributes, and indicators was developed via synthesis of structured conversations at national LTAR meetings. Early use revealed the need for a systematically inclusive process toward improvement. We designed and implemented an iterative decision‐making protocol to reach a consensus for a new version. The indicator framework differs from others in its attention to production and social outcomes and its grounding in networked agricultural science. Next steps entail developing web tools and personnel for AgPICKS that use LTAR's data and knowledge ecosystem to guide users in setting benchmarks of the desired conditions for their prioritized indicators, collect data, and visualize data to assess how well their management meets their benchmarks, toward the accurate measurement of management outcomes in a changing world.

The pursuit of sustainable phosphorus (P) management represents a long‐standing challenge in agricultural arenas, with far‐reaching implications for the environment and societal development. Few scholars are as synonymous with P science as Andrew Sharpley. Renowned over his 44‐year professional career for providing foundational insights into the fate and management of agricultural P, Sharpley also became the central figure in organizing responses to concerns over the contribution of non‐point source P pollution to eutrophication. As a global authority, Sharpley led teams that crafted scientific consensus for use by managers and policymakers in the face of complexity and uncertainty. His leadership offers lessons to those continuing in his footsteps and a model for all who desire to achieve scientific impact. This special collection of papers celebrates the perspectives, contributions, and legacy of Andrew Sharpley.

\papertype Original Article The pace of global change presents challenges for adequately assessing outcomes of agricultural management, hindering decision-making by producers, researchers, and consumers. The Long-Term Agroecosystem Research Network (LTAR) is in a unique position to advance monitoring to inform decision making. Here we describe how the network selected performance indicators designed to measure the tradeoffs from various farming and ranching approaches. Indicator selection was motivated by the need for common indicators that apply to the diversity of LTAR sites, but they are intended for widespread use by producers and other managers via the Agricultural Performance Indicator and Context Knowledge System (AgPICKS). An initial set of domains, attributes, and indicators was developed via synthesis of structured conversations at national LTAR meetings. Early use revealed the need for a systematically inclusive process toward improvement. We designed and implemented an iterative decision-making protocol to reach a consensus for a new version. The indicator framework differs from others in its attention to production and social outcomes and its grounding in networked agricultural science. Next steps entail developing web tools and personnel for AgPICKS that use LTAR’s data and knowledge ecosystem to guide users in setting benchmarks of the desired conditions for their prioritized indicators, collect data, and visualize data to assess how well their management meets their benchmarks, toward the accurate measurement of management outcomes in a changing world.

Excessive phosphorus (P) concentrations can lead to conditions that limit the amenity of freshwater resources. This problem is particularly acute in agricultural catchments, where P fertilizer and manure amendments have been used to increase soil fertility and productivity. In these catchments, P indices are often used to help target critical source areas in order to reduce P exports. However, the overall impact of agricultural mitigation efforts on receiving waters has not always been consistent with declines in total P exports from catchments. In this paper we propose a model of dissolved P mobilization (i.e., entrainment) in surface runoff that accounts for this outcome and examine modifications to P indices that better accommodate dissolved P mobilization. We suggest that dissolved P mobilization commences near the soil surface and has two phases. When water is first applied, labile P is mostly mobilized by dissolution and advection. Subsequently, as the supply of readily accessible P is exhausted, diffusion and hydrodynamic dispersion mobilize P from other sources at a near constant rate for the remainder of the event. As most P exports occur in larger (i.e., longer) events, the second phase appears responsible for most dissolved P exports. Such a model of dissolved P mobilization is consistent with runoff monitoring data under natural and simulated rainfall, suggesting that on low (shallow) slopes where the interaction between surface soil and water may be prolonged, dissolved P concentrations are likely to be higher. Dissolved P mobilization from low‐slope areas is not well represented in P indices at present. We suggest that there needs to be a more complex, mechanistic structure to P indices that involves additional compartmentalization. Further, we suggest that this can be achieved without losing the simplicity of P indices or flexibility to integrate research data and experiential knowledge into tools that are relevant to specific regions.

Legacy phosphorus (P) is a concept advanced by Dr. Andrew Sharpley and colleagues that was originally applied to the persistence of anthropogenic signatures in watersheds, and it has since been adopted in a diversity of settings to help guide the science and management of P. Following Sharpley's example to develop consensus‐based science, we considered contrasting perspectives on legacy P and defined legacy P as those stores within the environment that arise from historic human activity excluding “natural” or “background” geogenic sources. Legacy P is not restricted to one system or setting; it may reside in soils, sediments, biota, and water bodies. Legacy P has been estimated by fluxes (inputs minus outputs of P to a system) or, equivalently, by mass stocks (total minus geogenic). Because the origin of P in the environment cannot currently be directly quantified, we recommend that researchers report “total P” to track wider watershed P stocks and fluxes of P that include legacy P. We recognize that the definition of legacy P will continue to evolve as we continue to work toward consensus. Ultimately, the final definition of legacy P has consequences for the implementation and success of regulatory and voluntary strategies for legacy P management in agricultural systems. We support continued progress toward a consensus‐backed, research‐grounded definition for legacy P that is widely applicable yet useful for guiding management and policy.

The Long‐Term Agroecosystem Research (LTAR) network is a collaborative initiative funded by the U.S. Department of Agriculture, Agricultural Research Service, aimed at advancing sustainable, resilient agriculture through coordinated research conducted on croplands, grazing lands, and integrated crop/livestock systems. Here we provide an overview of the LTAR network, highlighting its vision, mission, initiatives, recent network activities, and future directions. Network‐level research is critical for developing contextually relevant solutions to the challenges faced by agricultural producers. Long‐term data collection, stakeholder engagement, and the integration of scientific knowledge are needed to enhance agricultural productivity and its resiliency, environmental quality, profitability, and social well‐being into the future.

The buffering of phosphorus (P) in the landscape delays management outcomes for water quality. If stored in labile form (readily exchangeable and bioavailable), P may readily pollute waters. We studied labile P and its intensity for >600 soils and sediments across seven study locations in the United States. Stocks of labile P were large enough to sustain high P losses for decades, indicating the transport‐limited regime typical of legacy P. Sediments were commonly more P‐sorptive than nearby soils. Soils in the top 5 cm had 1.3–3.0 times more labile P than soils at 5–15 cm. Stratification in soil test P and total P was, however, less consistent. As P exchange via sorption processes follows the difference in intensities between soil/sediment surface and solution, we built a model for the equilibrium phosphate concentration at net zero sorption (EPC₀) as a function of labile P (quantity) and buffer capacity. Despite widely varying properties across sites, the model generalized well for all soils and sediments: EPC₀ increased sharply with more labile P and to greater degree when buffer capacity was low or sorption sites were likely more saturated. This quantity–intensity–capacity relationship is central to the P transport models we rely on today. Our data inform the improvement of such P models, which will be necessary to predict the impacts of legacy P. Further, this work reaffirms the position of labile P as a key focus for environmental P management—a view Dr. Sharpley developed in the 1980s with fewer data and resources.