Forest Science, 60:1 (2014) 157-169.

DOI: 10.5849/forsci.12-158


Growth of midrotation pine plantations in the southeast United States tends to be limited by nitrogen (N) and phosphorus (P). Routine applications of urea and diammonium phosphate ameliorate N and P deficiencies; however, questions concerning what other nutrients are likely to be limiting growth are being raised. Consequently, a trial series with 23 study installations was established in loblolly (Pinus taeda L.) stands, aged between 9 and 25 years, with the aim of determining whether stands would respond to potassium (K) additions once the N and P deficiencies were corrected and whether the application of a full suite of macro- and micronutrients would further increase growth. On average, N plus P applications resulted in a mean growth improvement over unfertilized controls of 3.71 m3 ha−1 year−1 for 8 years after fertilization. Further growth improvements in response to the application of K, either with the N and P, or together with a range of macro- and micronutrients, were found to be dependent on location. Studies located on Pleistocene terraces, between 10 and 65 m in elevation, associated with ancient sea levels including the Talbot, Penholloway, Wicomico, Sunderland, and Coharie terraces of Georgia and the Carolinas, showed a smaller than average positive response to the addition of N and P (2.66 m3 ha−1 year−1), with further increases in growth when K was applied as well (additional 1.33 m3 ha−1year−1) and a further increase when a complete suite of nutrients was added (additional 2.59 m3 ha−1 year−1). Studies located elsewhere in the South showed an average response to the addition of N and P (mean improvement of 4.28 m3 ha−1 year−1), with no improvement in growth when additional nutrients were added. These results can assist foresters in identifying stands that are potentially responsive to applications of nutrients other than N and P.

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