Estimating soil ammonium adsorption using pedotransfer functions in an irrigation district of the North China Plain

Abstract

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen (NH 4 + -N) in soil. Desorption and leaching of NH 4 + -N has led to pollution of natural waters. The adsorption of NH 4 + -N in soil plays an important role in the fate of the NH 4 + -N. Understanding the adsorption characteristics of NH 4 + -N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions (PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture (silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH 4 + -N adsorption capacity than sandy loam soils. Clay and silt contents significantly affected the adsorption capacity of NH 4 + -N in the different soils. The adsorption isotherms of NH 4 + -N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay, silt, and organic carbon contents and Fe 2+ and Fe 3+ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH 4 + -N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH 4 + -N adsorption at a regional scale in irrigation districts.