Interseeded legumes with loblolly pine. II. Effect of phosphorus and legume variety on the growth of pine seedlings

A field study was initiated to quantify growth attributes of loblolly pine (Pinus taeda L.) when intercropped with warm-season annual legumes. In addition to main treatments, subplots of phosphorus (P) and a cool-season annual legume were also evaluated as factors contributing to growth of pine trees. After 3 years, pine seedlings grown with 'Iron and Clay' cowpea [Vigna unguiculata (L.) Walp.] had grown to a height of 315 cm and had a diameter of 63 mm which was a substantial increase when compared to plants receiving other treatments. Phosphorus application had no effect (P>.10) on pine growth parameters. The addition of 'Tibbee' crimson clover (Trifolium incarnatum L.) affected height (P<.10) of pine trees grown with 'Comanche' partridge pea (Cassia fasciculata Michx), and pine trees grown alone (control). Regression analyses indicated no correlation between rate of growth in height of pine trees and warm-season legumes over a three-year period. Growth rate in diameter during this period, however, was greatest for pine trees growing with cowpeas. Pine seedlings grown as a control or with alyceclover had similar diameter growth rate, but then grew slower than pines with cowpeas, and faster than pines grown with partridge peas.