Evaluation of phosphate sorption capacity and external phosphorus requirement of some agricultural soils of the southwestern Ethiopian highlands

<span>One of the most soil fertility management problems for crop production on acidic soils of the Ethiopian highlands is phosphorus fixation. The research was executed to assess the P-sorption capacity and to determine the external P requirement of different acidic soils in the Southwestern highlands of Ethiopia. Phosphorus sorption capacity (Kf) and its relation with selected soil characteristics were assessed for some major agricultural soils in the Ethiopian highlands to answer the questions, ‘What are the amount of P-sorption capacity and external P requirement of Nitisols, Luvisols, Alisols, and Andosols in Ethiopia?’. Twelve surface soil samples (at depth of 0-30 cm) were gathered and the P-sorption capacity was estimated. Phosphorus-sorption data were obtained by equilibrating 1 g of the 12 soil samples with 25 ml of KH₂PO₄ in 0.01 M CaCl2, having 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330 mg P L^-1 for 24 hours. The data were adjusted to the Freundlich adsorption model and the relationship among P-sorption and soil characteristics was established by correlation analysis. Clay content and exchangeable acidity, organic matter, Al₂O₃, and Fe₂O₃ oxides have affected phosphorus-sorption at a significance level of (P &lt; 0.05). Alisols had the highest Kf value (413 mg kg^-1) but Nitisols had the lowest Kf (280 mg kg^-1). The external phosphorus fertilizer requirement of the soils was in the order of 25, 30, 32, and 26 mg P kg^-1 for Nitisols, Luvisols, Alisols, and Andosols sequentially. The Kf varies among different soil types of the study area. The magnitude of the soil’s Kf was affected by the pH of the soil, soil OM content, and oxides of Fe and Al. Therefore, knowledge of the soils’ P retention capacity is highly crucial to determine the correct rate of P </span><span>fertilizer</span><span> for crop production.</span>

Washing and Heat Treatment of Aluminum-Based Drinking Water Treatment Residuals to Optimize Phosphorus Sorption and Nitrogen Leaching: Considerations for Lake Restoration

Drinking water treatment residuals (DWTRs) generated during drinking water treatment have been proposed for use in lake restoration as a solid-phase sorbent to inactivate phosphorus (P) in lake sediment. However, treatments that minimize leaching of nitrogen (N) and optimize P sorption capacity may be necessary prior to use. This study assessed seven different treatment methods, including washing and heat treatments at different temperatures and with and without oxygen limitation, among two DWTRs from Thailand. Results showed that oxygen-limited heat treatment at 600 °C substantially reduced N leaching (<0.2 mg/kg TKN) while also improving P sorption capacity (increase of 18–32% compared to untreated DWTR) to a maximum of 45.7 mg P/kg. Washing with deionized water reduced N leaching if a sufficient volume was used but did not improve P sorption. Heating at 200 °C with or without the presence of oxygen did not improve N leaching or P sorption. Regression of P sorption parameters from a two-surface Langmuir isotherm against physio-chemical properties indicated that oxalate-extractable (i.e., amorphous) aluminum and iron were significantly associated with total P sorption capacity (R2 = 0.94), but micropores and oxalate-extractable P modulated the P sorption from high-affinity to low-affinity mechanisms. In conclusion, this study confirmed the importance of amorphous aluminum in DWTRs for inactivating P, and the results suggest that high-temperature treatment under oxygen-limited conditions may be the most reliable way to optimize DWTRs for environmental remediation applications.

The Future of Phosphorus Use in Agriculture

Securing the nutritional needs for our increasing population will continue to drive a healthy demand for P. Innovation will continue to broaden our viable choices for P, which combined with social drivers, will continue to generate momentum towards a more closed P cycle. Further advances in plant breeding, agronomy, and fertilizer technology are required for today’s agricultural systems on soils with high P sorption capacity.

Effect of Flooding Time on Phosphate Adsorption Desorption Characteristics of Two Acid Soils

In a laboratory incubation study, two soils were treated with distilled water, and flooded for a period of 0 (contr-ol), 1, 2, 3, 4, 8 weeks. P adsorption desorption characteristics of two soils were measured at the end of the incubation period. P a-dsorption increased with increasing levels of added P in two soi-ls. P adsorption of Paddy soil was comparatively lower than that of upland red soil. P adsorption data was found to fit Langmuir isotherms for two soils. Soil P adsorption maxima obtained from Langmuir isotherm varied from 1190 to 672 mg/kg for upland r-ed soil, and varied from 708 to 530 mg/kg for paddy soil. Floodi-ng decreased P adsorption capacity of upland red soil,increased soluble P (in 0.01M CaCl2) and equilibrium P concentration. For paddy soil, there was a large increase in the P sorption capacity after one week flooding, and then P sorption capacity decreased. The more adsorption maxima is, and the more desorption maxi-ma (Dm) is. Desorption rate constant (Kd) and bonding energy (b) varied inconsistently in two soils.

Phosphorus sorption capacity of different types of opoka

Phosphorus sorption capacity of different types of opoka The bedrock opoka has been lately reported as an appropriate reactive media for onsite wastewater treatment systems due to its high phosphorus (P) sorption capacity. However, variations on its chemical composition may affect its reactivity with P, therefore leading to a variable P removal efficiency. In this paper, the P-sorption capacity of three different types of opoka from the region of Miechów, Poland, is reported. According to the silica and carbonate content, opoka samples were classified as light-weight and heavy-weight opoka. When heated over 900°C, opoka showed a very high P-sorption capacity that was well correlated to its Ca content. P-sorption isotherms from batch experiments with an artificial P solution were plotted and fitted to the Langmuir and Freundlich adsorption models. The Freundlich isotherm appeared to model better the P-sorption of light opoka and the Langmuir isotherm of heavy opoka, suggesting different dominating mechanisms of P-sorption by light and heavy opoka.

Extractable iron and aluminium predict the P sorption capacity of Thai soils

The objective of this study was to determine if dithionite- and oxalate-extractable Fe and Al can be used to predict the P sorption capacity of Thai soils. Forty-five samples from diverse soil types were taken from surface and subsurface horizons of soils on sandstone, shale/limestone, granite, and basalt. The samples were analysed for P sorption, dithionite- and oxalate-extractable Fe and Al (Fed, Feo, Ald, Alo), specific surface area (SSA), and other soil properties. Generally P sorption data for these soils were slightly better fitted by the Langmuir equation than the Freundlich equation. The Langmuir P sorption maximum ranged from 35 to 1111 μg/g with a median value of 370 μg/g soil. Soils developed on basalt had higher values of P sorption maximum (xm) (range 400–1111 μg/g, median 597 μg/g) than soils on other parent materials. Fed concentrations in soils (4–74 g/kg) were much higher than Feo concentrations (0.2–13.8 g/kg) with values of Feo/Fed ranging from 0.01 to 0.28 (median 0.09), indicating that most of the free iron oxides were crystalline. Amounts of Ald and Alo were about equal with median values of 1.6 and 1.0 g/kg, respectively. About 80% of the samples had SSA values <40 m2/g. Both the P sorption maximum and Freundlich k were linearly related to SSA (R2 = 0.77, 0.74), Ald (R2 = 0.78, 0.79), Alo (R2 = 0.64, 0.74), Fed (R2 = 0.48, 0.41), Feo (R2 = 0.43, 0.72), and clay content (R2 = 0.48, 0.36). Stepwise regression indicated that 81% of the variability in P sorption by these soils could be explained by a combination of dithionite and oxalate Fe and Al, however, Ald alone is almost as effective in predicting the P sorption capacity of Thai soils.