Chemical Distribution of Phosphorus in Soils used during the Development of Sorption Isotherms

Abstract

This study was developed to provide initial information on the chemical distribution of P into the different soil P pools after a soil sample underwent P sorption using 17 soil samples from the united States (13) and Brazil (4). During the sorption phase, soil samples were equilibrated with solutions containing increasing P concentrations (0-75 mg P l -1 ) following standard procedures. Following the sorption phase, the soil samples were allowed to air dry for 72 h and underwent a chemical fractionation (in water, anionic resin, 0.5M NahCo 3 , 0.1M Naoh, and 1.0M hCl). A wide range of sorption strength ranging from 0.043 to 0.289 l kg -1 and a maximum sorption ranging from 189 to 789 mg kg -1 were observed. More than 59% of the sorbed P was found in the water + resin fraction, which is considered the most labile pools where the binding energy is assumed to be low. In contrast, less than 25% of the sorbed P was found in the nonlabile pools where the binding energy is assumed to be the greatest. Although less than 25% of the sorbed P was found in the non-labile pools, the Naoh+hCl fraction contributed 2 to 61% of the overall sorption strength estimated for the soils studied. The results of this study suggest that sorption strength calculated from sorption studies are heavily skewed toward the nonlabile fraction, which was found to constitute a very small portion of the binding sites occupied during sorption studies.Abbreviations: b, the sorption maximum; ICP-OES, inductively coupled plasma optical emission spectroscopy; b f , sorption maximum determined using the sequential fractionation data; b i , sorption maximum estimated using the method of Nair et al. (1984); k, a coefficient unique to each soil that has been used as a measure of the sorption strength between soil particles and P; k f , the sorption strength parameter determined using the sequential fractionation data; k i , the sorption strength parameter estimated using the method of Nair et al. (1984); OM, organic matter; P i , inorganic P; P o , organic P; W kft , cumulative weighted sorption strength. W hen P is added to soils in the form of fertilizer, a series of reactions takes place, ranging from diffusion of P from the fertilizer granules into the soil solution, sorption of P into soil particles, and, with time, P precipitation (Hedley and McLaughlin, 2005). In the soil, inorganic P (P i ) will adsorb or precipitate by chemically binding with Al, Fe, or Ca (Lombi et al., 2006;Khatiwada et al., 2012;Eriksson et al., 2015). The solubility of phosphorus in soil is controlled by several factors, including how much P is originally adsorbed in the soil, how much P is precipitated in the soil, the soil pH, clay mineralogy, organic matter content, what types of minerals were formed during P precipitation, and the concentration of Ca, Al, Fe, and other cations in solution (Delgado and Torrent 2000;Violante and Pigna, 2002;Shigaki and Sharpley 2011;Weng et al., 2012;Eriksson et al., 2015;Gérard, 2016). McLaughlin et al. (2011) has shown that the amount of Ca...

Phosphorus adsorption characteristics in forested and managed podzolic soils

“…The increase of Mehlich-3 P in the C horizon might be due to apatite dissociation (Sen Tran, Giroux, Guilbeault, & Audesse, 1990) or, less likely given the Al-rich overlaying B horizon, indicative of downward P mobility. The Mehlich-3 P has an inverse and significant correlation with Al and silt content and a positive correlation with SOM and EC (Table 4); these trends were previously reported for acid soils (Daly et al, 2015;Schmitt et al, 2017). The Podzols in this study have a P saturation index (P/Al + Fe) lower than agricultural soils of Ontario or Maritime provinces of Canada (Table 2) .…”

“…In the tested soils, and likely in other Podzols in Nfld, multiple compounds, Al and Fe hydroxy(oxides), SOM, and metal‐organic acid chelates (Grand & Lavkulich, 2013; Väänänen et al., 2007; Villapando & Graetz, 2001) are likely responsible for P retention as described here by the Freundlich model and the multivariate analysis (Tables 4 and 5). The P adsorbed by the recently converted Nfld mineral soils is potentially fixed in nonlabile P pools, whereas labile P pools might gradually increase in long‐term managed soils (managed SJRDC) when soil fertility improves (Schmitt et al., 2017; Yang et al., 2019).…”

Soil types select for plants with matching nutrient‐acquisition and ‐use traits in hyperdiverse and severely nutrient‐impoverished campos rupestres and cerrado in Central Brazil

“…Total soil [P] was greater in soils associated with cerrado than in those associated with campos rupestres , while soil resin [P] indicated lower P availability in the cerrado . These lower values are associated with the P fraction bound to Fe and Al oxides in the soils associated with cerrado (Schmitt, Pagliari, & do Nascimento, ). However, leaf [P] was greater in plants growing on soils associated with cerrado , indicating that they are capable of taking up P bound to Al and Fe oxides (Table ), most likely through the roots releasing carboxylates (Lambers, Martinoia, & Renton, ).…”

Plant-Available Phosphorus in Highly Concentrated Fertilizer Bands: Effects of Soil Type, Phosphorus Form, and Coapplied Potassium

“…The reasons for the inconsistent and generally low impact of coapplication of K on potentially plant-available P concentrations in the acid soils remain unclear. For example, KCl coapplication with MCP or MAP has been reported previously to strongly decrease soil pH within bands. ,, Ernani and Barber suggested that coapplied K increases specific surface adsorption of P with variable charges due to a pH or a salt effect. − It is assumed that adsorbed P remains largely in an exchangeable form, , and such an effect could indeed explain changes in P w and net E 24h in the variably charged Ultisol and Alfisol. However, about 1.2 to 1.8 g P, or less, is generally deemed sufficient to saturate the maximum P sorption capacity of 1 kg soil .…”