Effect of phosphorus status of the soil on selenium availability

Due to its importance for human and animal health, low bioavailability of selenium (Se) is of concern in large parts of the world. Among the factors determining Se availability is competition for binding sites by other anions. In order to evaluate the effect of different soil P status on Se availability from fertilizer, adsorption studies were conducted with soils ranging from low to very high available P as measured in ammonium lactate (P‐AL) and addition of Se as either selenate or selenite. Generally selenite, and to some extent also selenate, adsorption decreased with increasing P‐AL status of the soil. However, in a silt loam, the increase in P‐AL from 140 (high) to 210 mg P kg^–1 (very high) did not result in a corresponding decrease in Se adsorption. Phosphorus saturation, on the other hand, was found to be lower in the sample that was very high in available P, suggesting that both the total amount of P on binding sites and the amount of plant‐available P influence Se availability. Selenate addition caused an increase in P availability, especially when added together with phosphate to a silt loam with very high P‐AL status.