Soil retention and subsequent uptake of nitrogen 2 years following operational rates of fertilization in loblolly pineThis article is part of a larger document. View the larger document here.
In this experiment, 15N-labelled fertilizers were used to trace nitrogen uptake, assimilation, and fate in four loblolly pine (Pinus taeda) stands fertilized with 224 kg ha-1 of elemental nitrogen (N) in the Southeastern United States. The fertilizer treatments included a non-fertilized control, urea, and three different enhanced efficiency N fertilizers. Two years after fertilization, soil from the upper 15 cm in each of five treatments from four different locations was collected. A greenhouse study was established to examine the availability of the residual fertilizer N in the soil. Two bare-root loblolly pine seedlings were planted in each of five replicate pots for a total of 200 seedlings in 100 pots. Total soil N, soil N availability, and seedling N uptake was measured periodically over 15 weeks, and the 15N to 14N ratio was analyzed on soil and seedlings prior to planting and at harvest. Significant (alpha = 0.05) increase in 15N to 14N ratio was found in seedlings 3 weeks after planting in the fertilized treatments. We determined that significant (alpha = 0.05) amounts of residual fertilizer N following operational fertilization was available to loblolly pine seedlings 2 years after application.