Differences in the recovery of four different nitrogen containing fertilizers after two application seasons in pine plantations across the southeastern United States

Abstract

The ecosystem recovery of four nitrogen (N) containing fertilizers (urea and three enhanced efficiency fertilizers [EEFs]) enriched with 15N were compared at five different sites with single treatment replication per site for both a spring and summer application in mid-rotation loblolly pine (Pinus taeda L.) stands across the southeastern United States. Total ecosystem fertilizer N recovery was greater for all EEFs (78–84%) compared to urea (52%) with no differences among individual EEFs or between seasons. Fertilizer N recovery in the soil (forest floor+0–30cm) was greater for EEFs (36–43%) compared to urea (21%), with no significant treatment differences in fertilizer N recovery in the canopy (14–22%), stem (5–8%), or roots (11–14%). When individual ecosystem components were analyzed, the greatest difference in fertilizer N recovery occurred in the 0–15cm mineral soil for EEFs (27–31%) compared to urea (13%). Differences for the same fertilizer treatment between the season of application were generally minor. Despite these minor differences between season of application, there was a general trend for higher fertilizer N recovery in the crop trees for all treatments for the spring fertilization compared to a higher fertilizer N recovery in the soil after the summer fertilization. Numerous treatment differences also occurred in individual ecosystem components for δ15N values (‰) and N concentrations within the same season, but only occasional differences between seasons. This research highlights an increased fertilizer N recovery and ecosystem partitioning of fertilizer N using EEFs compared to urea in southeastern pine plantations, regardless of the application season, and potentially translate to an increase in the fertilizer N use efficiency of these pine plantations.