Abstract

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 m(3) 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 m(3) ha(-1) year(-1)), with further increases in growth when K was applied as well (additional 1.33 m(3) ha(-1) year(-1)) and a further increase when a complete suite of nutrients was added (additional 2.59 m(3) 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 m(3) 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.