Kinetics of phosphorus sorption in soils in the state of Paraíba¹

Abstract

SUMMARYThe soil P sorption capacity has been studied for many years, but little attention has been paid to the rate of this process, which is relevant in the planning of phosphate fertilization. The purpose of this experiment was to assess kinetics of P sorption in 12 representative soil profiles of the State of Paraíba (Brazil), select the best data fitting among four equations and relate these coefficients to the soil properties. Samples of 12 soils with wide diversity of physical, chemical and mineralogical properties were agitated in a horizontal shaker, with 10 mmo L -1 CaCl 2 solution containing 6 and 60 mg L -1 P, for periods of 5, 15, 30, 45, 60, 90, 120, 420, 720, 1,020, and 1,440 min. After each shaking period, the P concentration in the equilibrium solution was measured and three equations were fitted based on the Freundlich equation and one based on the Elovich equation, to determine which soil had the highest sorption rate (kinetics) and which soil properties correlated to this rate. The kinetics of P sorption in soils with high maximum P adsorption capacity (MPAC) was fast for 30 min at the lower initial P concentration (6 mg L -1 ). No difference was observed between soils at the higher initial P concentration (60 mg L -1 ). The P adsorption kinetics were positively correlated with clay content, MPAC and the amount of Al extracted with dithionite-citratebicarbonate. The data fitted well to Freundlich-based equations equation, whose coefficients can be used to predict P adsorption rates in soils.Index terms: Adsorption, kinetic equations, phosphate, tropical soils, semi-arid soils.( de P, pelos períodos de 5, 15, 30, 45, 60, 90, 120, 420, 720, 1.020

Organic acid coated-slow-release phosphorus fertilizers improve P availability and maize growth in a tropical soil

“…Santos et al (2011) found that adsorption of 74% of the added P occurred within 5 min in soil with a high P sorption capacity (0.3473 mg g -1 ). More recently, Guedes et al, (2016) studying P adsorption and desorption kinetics using a stirred-flow system, observed that most of the P adsorption process occurs in the first minutes of contact with the solution.…”

Phosphorus availability as a function of its time of contact with different soils

“…(1) According to methodology described in EMBRAPA (1997); (2) Data presented in Santos et al (2011), according to EMBRAPA (2006: RR -Regolithic Neosol, PAC -Grey Argisol; TX -Haplic Luvisol; PVA -Red-Yellow Argisol; PVd -Dystrophic Red Argisol; VX -Haplic Vertisol; (3) Remaining phosphorus (Alvarez V. et al, 2000); (4) The experiment was carried out in a randomized block design with 6 soil classes, 7 incubation times and 4 doses, with three replicates; each experimental unit consisted of one polyethylene pot without drain, with 2.8 dm 3 of soil and two maize plants.…”

“…In these studies, most soils have high maximum phosphate adsorption capacity (MPAC) and high contents of Fe and Al oxides, characteristics that are different from those of soils of the Northeast region. Therefore, it raises the hypothesis that, in Northeast soils, P sorption exists, but the magnitude and irreversibility of this sorption are small (Broggi et al, 2010;Santos et al, 2011;Souza Júnior et al, 2012).…”

Phosphate Sorption onto Structured Soil

“…It is also to be considered that the soil composition of the accessible and inner part of the aggregates might differ from the fine earth. The, in general, great heterogeneity of soil in physical, chemical, and mineralogical aspects in the solid-state, and also regarding soil solution, has to be considered in explaining the data [22,52]. Although the sorption process is predominantly assumed to be a surface phenomenon [25,53], structured soils may withdraw molecules from the advectively moving soil water.…”