The Transport of Bioavailable Phosphorus in Agricultural Runoff

Abstract

Bioavailable P (BAP) in agricultural runoff represents P potentially available for algal uptake and consists of soluble P (SP) and a variable portion of participate P (PP). Evaluation of the impact of agricultural management on BAP in runoff will aid assessment of the resultant biological productivity of receiving water bodies. Soluble P, PP, and bioavailable PP (BPP) (estimated by NaOH extraction) were determined over a 5‐yr period in runoff from 20 unfertilized and fertilized, grassed, and cropped watersheds in the Southern Plains. Soluble P, BPP, and BAP loss in runoff was reduced by practices minimizing erosion and runoff, with respective mean annual amounts ranging from 237 to 122, 1559 to 54, and 1796 to 176 g P ha−1 yr−1 (for peanut‐sorghum [Arachis hypogaea L.‐Sorghum bicolor (L.) Moench] and native grass watersheds, respectively). However, as vegetative cover improved, BAP (SP plus BPP) comprised a larger portion of total P (TP) loss (29% for peanut‐sorghum and 88% for native grass). This results from an increasing contribution to BAP of SP (13% for peanut‐sorghum and 69% for native grass watersheds) and BPP to PP (26% for peanut‐sorghum and 69% for native grass watersheds). Clearly, P bioavailability is a dynamic function of physiochemical processes controlling erosion, particle size enrichment, P desorption‐dissolution reactions, and plant residue breakdown, in addition to soil and fertilizer P management. Hence, the change in trophic state of a water body may not be adequately reflected by TP inputs only. To more reliably evaluate the biological response of a water body to agricultural P inputs, particularly from conservation tillage practices, it may be necessary to determine BAP in runoff.

Nutrient transfer by runoff from sewage sludge amended soil under simulated rainfall

“…Phosphorus content ranges generally from 34 to 57 g P 2 O 5 kg −1 dry matter (Sommellier et al, 1996), but this content, as well as speciation (mineral/organic form), depends on original effluent composition and types of treatment (raw, digested or composted sludges). Surface runoff is the major cause of phosphorus loss from cultivated fields, and this process was shown to be closely linked to sediment transport (Sharpley et al, 1992). Nitrogen in sludge is mainly under organic forms, while mineral forms are generally in low concentrations and are mainly represented by ammonium nitrogen.…”

Dominant mechanisms for the delivery of fine sediment and phosphorus to fluvial networks draining grassland dominated headwater catchments

“…Although this may not be typical of agricultural catchments (e.g. Harrington and Harrington, 2014;Sharpley et al, 1992;Siwek et al, 2013), near-surface runoff as a conduit for effective P transfer has been highlighted in other headwater catchments, with the presence of field drains producing preferential hydrological pathways (Dils and Heathwaite, 1999;Hatch et al, 1999;Heathwaite et al, 2006;Heathwaite and Dils, 2000;Rhea et al, 1996;Sims et al, 1998). This sub-surface pathway will not only enable the movement of soluble P within the soil matrix, but also very fine colloidal material, which may contribute significantly to the export of TP and TRP (Foster et al, 2003;Heathwaite and Dils, 2000).…”

At-grade stabilization structure impact on surface water quality of an agricultural watershed

“…About 75e90% of TP in conventional agricultural runoff is in the PP form (Sharpley et al, 1994). Even though PP is not immediately available for plant uptake, it acts as a long-term source within sediment, although the bioavailability of PP has been shown to be quite variable (e.g., 10e90%; Sharpley et al, 1992). Total P concentrations in agricultural runoff have been shown to decrease with increased conservation and less intensive agricultural practices; however, bioavailable components of phosphorus (DP and bioavailable PP) were shown to represent a much greater proportion of the TP under increased conservation practices (Sharpley et al, 1992).…”

“…Even though PP is not immediately available for plant uptake, it acts as a long-term source within sediment, although the bioavailability of PP has been shown to be quite variable (e.g., 10e90%; Sharpley et al, 1992). Total P concentrations in agricultural runoff have been shown to decrease with increased conservation and less intensive agricultural practices; however, bioavailable components of phosphorus (DP and bioavailable PP) were shown to represent a much greater proportion of the TP under increased conservation practices (Sharpley et al, 1992). However, it should be noted that the particulate forms of any nutrient in freshwater systems represent a complex continuum of organic particles, microorgansims, and sorbed inorganic ions and that suspended sediment itself can be aggregated (Droppo, 2001).…”