Fertilizer Fate in a 13‐year‐old Slash Pine Plantation

Abstract Surface application of 403 kg N, 95 kg P, and 64 kg K per ha to a 13‐year‐old slash pine ( Pinus elliottii Englem. var. elliottii ) plantation on Caddo loam soil increased total volume growth during the next 6 years by 8.3 m 3 /(ha·year). Trees responded rapidly to the fertilizer; measurable differences in diameter growth developed by mid‐May. Fertilization markedly increased the amount of N, P, and K accumulated in current‐year needles during the first year after treatment. Fertilized trees continued to accumulate more P in current foliage for at least 8 years. Ratios of Rb/K in foliage indicated that K from the fertilizer comprised 27% of K accumulated in current‐year needles of fertilized trees during the fifth and sixth growing seasons, and 20% accumulated in the eigth. Ten months after treatment, added K had apparently disappeared from the top 13 cm of soil, but about half the added P remained available there. After 8 years, fertilized soil contained 40 ppm available P in the 0.9 cm layer; unfertilized soil contained only 2 ppm. In 8 years, fertilized plots accumulated 9.2 metric tons/ha more litter than did control plots. Litter had 50 kg/ha more N, 11.3 kg/ha more P, and 5.1 kg/ha more K than did litter on unfertilized plots. Disking to incorporate the fertilizer into the soil gave no advantage.