Soil change and carbon storage in longleaf pine stands planted on marginal agricultural lands

An increasing area of marginal agricultural land in the coastal plain of the southeastern United States is being planted to longleaf pine (Pinus palustris Mill.). This chronosequence study in southern Georgia evaluated the effect of pine planting and the associated cessation of agricultural activity such as tillage and fertilization on soil C storage and soil nutrient stocks. Soils are Arenic or Typic Kandiudults with coarse-textured surface soils. Soil C, nutrients, and bulk density from 0 to 50 cm in planted stands 1, 3, 7, and 14 yr old, as well as soils beneath natural longleaf pi-ne stands that were in a never tilled (NT) condition, were evaluated (n = 3 per stand age). No accumulation of soil C was apparent during the first 14 yr of pine growth. The average content of soil C in planted stands (11 +/- 1 Mg/ha; mean +/- 1 SE) was similar to 16 Mg/ha less than that in the NT soils (27 +/- 4 Mg/ha). Soil total N content within planted stands also did not differ by age, although extractable NO, declined rapidly. Despite agricultural N inputs, the mean N content of planted stands (410 +/- 83 Mg/ha) was below that in NT stands (730 +/- 21 Mg/ha). Total P (1507 +/- 21 Mg/ha) and extractable P (113 -_ 21 Mg/ha) contents also did not differ between planted stands but had highly elevated values compared to total P (728 -_ 38 Mg/ha) and extractable P (2 +/- 1 Mg/ha) for NT soils. Soil exchangeable Ca, Mg, and K had generally decreasing contents with stand age but varying patterns related to NT soils. During the first 14 yr of reforestation, soils did not sequester C. Carbon benefits may be gained, however, in above-ground and belowground biomass accumulation and through the cessation of high energy-consumptive activities such as fertilization or tillage. Enhanced P fertility on these marginal lands can improve pine growth, but only if other elements such as N are not limiting to growth.