4R Management of Phosphorus Fertilizer in the Northern Great Plains

In northern regions, a high proportion of annual runoff and phosphorus (P) export from cropland occurs with snowmelt. In this study, we analyze 57 site-years of field-scale snowmelt runoff data from 16 small watersheds draining fine-textured soils (clay or clay loam) in Manitoba, Canada. These fields were selected across gradients of soil P (2.4 to 26.7 mg kg −1 , 0-to 15-cm Olsen P), tillage intensity (high frequency to long-term no-till), and fertilizer input. The strongest predictor of flow-weighted mean concentrations of total dissolved P (TDP) in snowmelt runoff was Olsen P in the top 5 cm of soil (r 2 = 0.45, p < 0.01). Residual variation in this relationship related positively to volumetric soil moisture and negatively to water yield. Although Olsen P levels were relatively consistent from year to year, suggesting control by long-term fertilization and tillage history, Olsen P stratification (ratio of 0-5/0-15 cm) increased with rates of fertilizer application. Particulate P (PP) comprised <34% of total P on average, and concentrations were not well predicted by soil or management characteristics. Loads of PP and TDP exported during snowmelt were primarily a function of water yield and size of accumulated snowpack; however, residual variation in the TDP relationship correlated positively with both soil moisture and Olsen P. Retention of runoff water on the landscape could reduce loads, but careful management of near-surface soil P is required to prevent snowmelt runoff losses of P at the source and to reduce the potential for the eutrophication of downstream aquatic ecosystems.

Section: Discussionmentioning

confidence: 99%

Near‐Surface Soils as a Source of Phosphorus in Snowmelt Runoff from Cropland

Wilson

Elliott

Macrae³

et al. 2019

“…Nutrient management (i.e., planning the source, rate, timing, and method P application), for example, is regarded as the main practice to avoid agricultural P losses and will be seen by most farmers as a valuable tool to help them apply P most profitably. Nutrient management is not discussed in detail in this paper as this topic is covered separately in this special section (Bruulsema et al, 2019; Grant and Flaten, 2019); we instead focus here on how applied P becomes vulnerable to all loss pathways depending on the source, rate, placement, and timing.…”

Section: Implementing Conservation Practices That Reduce Agriculturalmentioning

confidence: 99%

Increasing the Effectiveness and Adoption of Agricultural Phosphorus Management Strategies to Minimize Water Quality Impairment

Osmond

Shober²,

Sharpley

et al. 2019

Phosphorus (P) is essential for optimum agricultural production, but it also causes water quality degradation when lost through erosion (sediment‐attached P), runoff (soluble reactive P; SRP), or leaching (sediment‐attached P or SRP). Implementation of conservation practices (CP) affects P at the source (avoiding), during transport (controlling), or at the water resource edge (trapping). Trade‐offs often occur with CP implementation. For instance, multiple researchers have shown that conservation tillage reduces total P by over 50%, while increasing SRP by upward of 40%. Conservation tillage may increase water quality degradation as SRP is more bioavailable than is particulate P. Conservation practices must be implemented as a system of practices to increase redundancy and to address all loss pathways, such as P management with conservation tillage and a riparian buffer. Further, planning and adoption must be at a watershed scale to ensure practices are placed in critical source areas, thereby providing the most treatment for the least price. Farmers must be involved in watershed planning, which should include financial backstopping and educational outreach. It is imperative that CPs be used more effectively to reduce and retard off‐site P losses. New and innovative CPs are needed to improve control of P leaching, address legacy stores of soil test P, and mitigate increased P losses expected with climate change. Without immediate changes to CP implementation, P losses will increase due to climate change, with a concomitant degradation of water quality. These changes must be made at a watershed scale and in an intentional and transparent manner. Core Ideas Phosphorus‐reducing conservation practices must control all P pathways. Phosphorus‐reducing conservation practices must be utilized as systems. New and innovative conservation practices are needed to improve control of P. Farmer decision‐making must be considered when implementing conservation practices. Watershed planning and conservation practice implementation must be intentional.

“…Across diverse agroecosystems, Grant and Flaten (2019) describe how 4R management of P fertilizer use in the northern Great Plains—matching fertilizer rates to crop (small grains, oilseeds, and pulses) removal and banding fertilizer in or near the seed row at the time of seeding—provides the greatest P efficiency and long‐term sustainability and environmental protection in this region. Ippolito et al (2019) show how irrigation type influences soil P dynamics, noting a difference in soil P availability between sprinkler and furrow irrigation, with greater Olsen‐extractable P in long‐term furrow irrigation.…”

Section: Focusing On Place‐based Solutions: Think Globally Act Locallymentioning

confidence: 99%

Phosphorus mirabilis: Illuminating the Past and Future of Phosphorus Stewardship

Jarvie

Sharpley²,

Flaten³

et al. 2019

After its discovery in 1669, phosphorus (P) was named Phosphorus mirabilis (“the miraculous bearer of light”), arising from the chemoluminescence when white P is exposed to the atmosphere. The metaphoric association between P and light resonates through history: from the discovery of P at the start of the Enlightenment period to the vital role of P in photosynthetic capture of light in crop and food production through to new technologies, which seek to capitalize on the interactions between novel ultrathin P allotropes and light, including photocatalysis, solar energy production, and storage. In this introduction to the Journal of Environmental Quality special section “Celebrating the 350th Anniversary of Discovering Phosphorus—For Better or Worse,” which brings together 22 paper contributions, we shine a spotlight on the historical and emerging challenges and opportunities in research and understanding of the agricultural, environmental, and societal significance of this vital element. We highlight the role of P in water quality impairment and the variable successes of P mitigation measures. We reflect on the need to improve P use efficiency and on the kaleidoscope of challenges facing efficient use of P. We discuss the requirement to focus on place‐based solutions for developing effective and lasting P management. Finally, we consider how cross‐disciplinary collaborations in P stewardship offer a guiding light for the future, and we explore the glimmers of hope for reconnecting our broken P cycle and the bright new horizons needed to ensure future food, water, and bioresource security for growing global populations. Core Ideas This special section comprises 22 papers celebrating the 350th anniversary of P discovery. Historical and emerging challenges and opportunities exist in P research and understanding. Authors address P use efficiency and a kaleidoscope of challenges for efficient P use. Focusing on place‐based solutions is required for effective P management. Cross‐disciplinary collaborations in P stewardship are needed for food and water security.