Accessing Legacy Phosphorus in Soils

Abstract

Repeated applications of phosphorus (P) fertilizers result in the buildup of P in soil (commonly known as legacy P), a large fraction of which is not immediately available for plant use. Long-term applications and accumulations of soil P is an inefficient use of dwindling P supplies and can result in nutrient runoff, often leading to eutrophication of water bodies. Although soil legacy P is problematic in some regards, it conversely may serve as a source of P for crop use and could potentially decrease dependence on external P fertilizer inputs. This paper reviews the (1) current knowledge on the occurrence and bioaccessibility of different chemical forms of P in soil, (2) legacy P transformations with mineral and organic fertilizer applications in relation to their potential bioaccessibility, and (3) approaches and associated challenges for accessing native soil P that could be used to harness soil legacy P for crop production. We highlight how the occurrence and potential bioaccessibility of different forms of soil inorganic and organic P vary depending on soil properties, such as soil pH and organic matter content. We also found that accumulation of inorganic legacy P forms changes more than organic P species with fertilizer applications and cessations. We also discuss progress and challenges with current approaches for accessing native soil P that could be used for accessing legacy P, including natural and genetically modified plant-based strategies, the use of P-solubilizing microorganisms, and immobilized organic P-hydrolyzing enzymes. It is foreseeable that accessing legacy P will require multidisciplinary approaches to address these limitations.

Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

“…Similarly, McBride and Cherney [42] reported greater soil total P concentrations and higher forage P for New York farms with at least one application of biosolids compared to farms without biosolids applied. The buildup of bioavailable P in soils increases losses of P to surrounding water bodies and contributes to algal blooms [19][20][21]. Although the term "eutrophication" is most frequently applied to water bodies impacted by excess nutrients, particularly P and N, it can also be applied to soils and ecosystems [46], as high nutrient levels in soils can negatively affect soil fertility and ecosystem function and may be resistant to reversal or remediation [20].…”

“…Consequently, repeated farm application of biosolids almost invariably leads to irreversible buildup of excessive concentrations of P in surface soils, much of which is in available form [17,18]. This buildup increases losses of soil P to surrounding water bodies by leaching and erosion, with consequent water eutrophication and algal blooms [19][20][21]. While these critically important environmental consequences of excessive soil P are well-documented by the studies cited here, direct impacts of excessive P on soil fertility and plant growth have not generally been considered a significant risk and have rarely been investigated.…”

Challenges and Successes in Identifying the Transfer and Transformation of Phosphorus from Soils to Open Waters and Sediments

“…In this special issue, we invited research and review articles that address the topic of soil P processes involving transfer and transformation across the landscape, either presenting novel research methods or synergy among non-traditional research fields; a review of existing successes and failures with underlying causes; or data-driven recommendations on the various approaches necessary to mitigate P loss and achieve the tangible goal of improving water quality. This volume contains eight original research articles [6][7][8][9][10][11][12][13] and two review articles [14,15].…”

“…The two review papers took a holistic approach to cover an expansive area of P transformation processes along the cropland-riparian-stream continuum [15] and the assessment of legacy P [14]. The first review paper provided a broader assessment of P transformation and highlighted various approaches to improve and assess the effectiveness of riparian buffer zones in cold climate agroecosystems and highlighted the need of connecting hydro-biogeochemical and hydro-climatic data for the risk assessment on P loss to open waters.…”

“…The first review paper provided a broader assessment of P transformation and highlighted various approaches to improve and assess the effectiveness of riparian buffer zones in cold climate agroecosystems and highlighted the need of connecting hydro-biogeochemical and hydro-climatic data for the risk assessment on P loss to open waters. The chronic issue of legacy P was highlighted [14] by synthesizing the current knowledge of the bioaccessibility of different P forms, the transformations of P, and by proposing research and management approaches for potentially tapping legacy P for crop production.…”