| Abstract: | Two studies were conducted at the Texas Agricultural Experiment Station at Overton to assess facilitative effects of intercropping 3 selected warm season annual legumes with non-N-fixing species. A glasshouse study was initiated to determine and quantify direct nitrogen (N) transfer from legumes during the growing season. Annual 'Tifleaf' pearl millet (Pennisetum americanum L. Leeke) was grown in pots as a monoculture with and without N applied as inorganic fertilizer, or with either 'Iron and Clay' cowpeas [Vigna unguiculata (L.) Walp], common alyceclover [Alysicarpus vaginalis (L.) DC.], or 'Comanche' partridge pea (Cassia fasciculata Michx.). Pearl millet grown with partridge peas produced dry matter similar to pearl millet that received the equivalent of 112 kg N/ha. Pearl millet grown with legumes also contained lower levels of neutral detergent fiber than did pearl millet that received fertilizer. Alyceclover was determined to have directly transferred 63% of the N contained in the pearl millet tissue. Partridge peas and cowpeas transferred 34% and 32% of the N contained in pearl millet plants, respectively. Nitrogen content of pearl millet grown with legumes was not as great as pearl millet that received N-fertilizer. A field study was also conducted in which one-year-old loblolly pine (Pinus taeda L.) seedlings were established in a mechanically prepared, previously forested site. Cowpeas, alyceclover and partridge peas were then intercropped within the pine seedlings. Plots were split with a phosphorus application and split again (split-split plot) with a winter legume treatment. Partridge peas planted at 11 kg/ha suppressed the height of pine seedlings at 15 months, while diameter was not affected. Phosphorus fertilizer did not affect pine seedling growth, but did affect warm season and cool season annual legume production. The cool season annual legume crimson clover (Trifolium incarnatum L.) did not affect pine seedling growth during the first growing season. Warm season annual legumes did affect pine seedling mortality. Mortality was highest (P<0.05) for pine seedlings grown with alyceclover and partridge peas and least for pine seedlings grown with cowpeas or as monocultures. |
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