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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.

A study was conducted to determine the effects of legume companion crops and phosphorus (P) fertilizer on the growth and survival characteristics of newly established loblolly pine (Pinus taeda L.) seedlings. At 12 months post-establishment, there was no legume effect (P>0.05) on root lateral development or ropting depth for pine seedlings. Likewise, there was no legume effect (P>0.05) on aboveground biomass production of pine seedlings. Partridge pea (Cassia fasciculata Michx.) had a negative effect (P<0.05) on pine seedling total root biomass compared to other treatments. Pine seedlings grown with legumes allocated less resources to root development compared to pine seedlings grown alone. Pine seedlings grown alone or with cowpea [Vigna unguiculata (L.) Walp.] were subject to less mortality (P<.05) than seedlings grown with alyceclover [Alysicarpus vaginalis (L.) DC] or partridge pea. Phosphorus fertilization enhanced dry matter (DM) yield of legumes but had no effect on rooting depth of pine seedlings during the first 12 months of growth. After 12 months post-establishment, the most pronounced effect of P fertilization was that of increased nitrogen (N) content of leaf, stem, and roots of pine seedlings. Native, annual herbaceous grass biomass in the control plots (no legume) reduced the amount of soil N to below pre-planting levels, while soil N levels in all legume plots exceeded pre-trial levels.