Phosphorus sorption characteristics of amended LPA soils cultivated to oil palm seedlings
Abstract
This study evaluated the effect of four amendments: raw, composted, and pyrolyzed oil palm empty fruit bunch in modified forms applied at the rate of 75 kg K ha-1 and NPKMg fertilizer; on their on phosphorus (P) sorption characteristics of three soil types (Lixisol, Plinthosol, and Acrisol). The research was carried out at the Ohosu experimental station of the Nigerian Institute for Oil Palm Research (NIFOR), Edo State, Nigeria (Latitude 60 39' 90.8'' N - 60 39' 74.5'' N and Longitude 50 7' 33.3'' E – 50 9' 46.9''E) between November 2018 and December 2019. The soils used for the phosphorus study were arranged in a Completely Randomized Design with three replicates and incubated for two weeks. Soil samples were collected and analyzed for P sorption at 2 weeks after incorporation (WAI). The available P in the soil was extracted using the Olsen extract method, and the concentration of P in the clear extract was determined by the ascorbic acid method. Phosphorus that disappeared from the solution was considered as sorbed P which was plotted against P concentration in the solution to obtain a P sorption isotherm. Data collected were subjected to sorption isotherms (Langmuir, Freundlich, and Temkin), Analysis of Variance, and regression analysis. Treatment means were separated using the Least significant difference (p≤0.05). The results showed that there was a general increase in the amount of P-sorbed as the concentration of the phosphate solution increased. Lixisol amended with compost showed the highest P-sorbed at 55 mg/kg, a similar trend was observed in the Plinthosol amended with NPKMg showed the highest P-sorbed at 57 mg/kg. Furthermore, Acrisol amended with biochar gave the highest P-sorbed at 55 mg/kg. P - sorption results showed that Lixisol amended with raw empty fruit bunch had the highest sorption efficiency in the range of 71.12 to 99.96%, indicating high affinity and high adsorption capacity. The Freundlich isotherm gave the best fits with an R2 value of 0.999 for Lixisol, and Plinthosol treated with biochar and compost, and Acrisol treated with biochar. The models were linearly correlated with the P sorbed. The Langmuir model was in the range for Lixisol 0.177 – 0.918, Plinthosol 0.665 – 0.952, and Acrisol 0.008 – 0.917, indicating that not all the amended soils fit the model. Data presented, fit the Freundlich model with Lixisol range between 0.987 and 0.999, Plinthosol 0.959 – 0.998, Acrisol 0.992 – 0.999. The study concluded that Lixisol and Acrisol with biochar or compost exhibited higher P- sorption.
