The effect of soil phosphorus on particulate phosphorus in land runoff

Abstract

Accumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19-194 mg Olsen-P (OP) kg À1 ) on the concentrations of particulate P (PP), and sorption properties (Q max , k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 mg litre À1 per mg OP kg À1 of soil, but this rate was approximately 50% of the rate of increase in dissolved P (< 0.45 mm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean þ 57%) than the soil because of enrichment with fine silt and clay (0.45-20 mm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (P sat ; 15-42%) and equilibrium P concentration (EPCo; 0.7-5.5 mg litre À1 ) in the SS fell within narrower ranges compared with the soils (6-74% and 0.1-10 mg litre À1 , respectively). When OP was < 100 mg kg À1 , P sat and EPCo values in the SS were smaller than those in the soil and vice-versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P > 0.05) effect on the P sat , or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.

Effect of agronomic management on risk of suspended solids and phosphorus losses from soil to waters

“…Especially in the manured plot, where P surplus was very high, soil and dispersed solids were similarly saturated, confirming that this soil has reached the maximum P sorption capacity to buffer further P addition and accounting for the higher soluble P content. Withers et al (2009), studying collected sediments from overfertilised soils, showed that the suspended solids were more saturated than the relative bulk soil on plots with Olsen P<100 mg kg −1 , whilst the inverse occurred in soils with higher Olsen P levels and the suspended solids changed from being a source to sink of P. Moreover, the finest particles detached were Cenriched and depleted in poorly crystallised Fe and Al oxides. Particle composition and P sorption may affect surface electrical charge and, hence, soil dispersibility (Celi and Barberis 2005).…”

Integrating legacy soil phosphorus into sustainable nutrient management strategies for future food, bioenergy and water security

“…For example, Dodd et al (2012) estimated it would take between 23 and 44 years to lower STP sufficiently to reach a solublereactive P (SRP) concentration of 0.02 mg L -1 in runoff from grazed grassland required for eutrophication control. Even longer timescales can be expected to reduce the P content of eroding soil particles due to their insensitivity to changes in STP in agricultural settings (Withers et al 2009). Lowering of STP and SRP release to runoff may also be more difficult to achieve in agricultural systems that rely on no-till, crop residue and cover crop management techniques that concentrate available soil P at the surface (Smith et al 2014).…”

Phosphorus Release Characteristics from Biosolids-Derived Organomineral Fertilizers

“…This occurs because of the combined effect of relatively low N:P ratios of biosolids (typically less than 1) with soil applications based entirely on N requirements by crops, which results in over-application of P relative to crop requirements. Surplus of phosphorus in soils receiving periodic applications of biosolids influences soil P dynamics and can enhance transport of P to water courses when the soil sorption capacity is exceeded (Smith et al 2006;Withers et al 2009). Therefore, understanding the availability of P from organic-based fertilizers applied to soil is an important agronomic and environmental consideration for nutrient management.…”