Interseeded legumes with loblolly pine. I. Effect of phosphorus and legume variety on pine seedling establishment and mortality

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.