Slash pine growth and nitrogen leaching potential following fertilization and pinestraw removal

Abstract

AbstractCommercial pine plantations in the southern United States are commonly fertilized to enhance growth and to replenish nutrients following timber harvests or repetitive raking of pinestraw, an important secondary product. We examined the effects of pinestraw removal and fertilization on pine growth and N leaching potential in an 8‐yr‐old slash pine (Pinus elliottii Engelm.) plantation in North Florida. Raking treatments (raked or nonraked) were applied annually in February 2014–2017. Fertilization treatments (controlled‐release polymer‐coated urea at 0, 28, 56, 140, or urea at 56 kg N ha–1 yr–1) were applied annually in June 2014–2016. Pinestraw removal had no effect on stand growth. Fertilization did not enhance pine growth and increased mortality at the highest application rate. All fertilized treatments raised ammonium N (NH4–N) and nitrate–nitrite N (NOx–N) concentrations in soil solution at 30‐cm depth, indicating increased leaching potential. The period of elevated NH4–N concentrations occurred from 1 to 4 wk after fertilization, and the period of elevated NOx–N concentrations occurred from 1 to 13 or 26 wk following fertilization, with NOx–N concentration peaks (up to 98 mg L–1) at 4 or 8 wk. Soil solution NH4–N and NOx–N concentrations increased with increasing N application rate and with consecutive fertilizations. Polymer‐coated urea had no advantage over urea in terms of pine growth but resulted in slightly lower soil solution NOx–N concentrations in raked plots.