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Nodulation, Nitrogen Fixation, and Early Growth of Arrowleaf Clover in Response to Root Temperature and Starter Nitrogen

Southern Plains Area Conservation & Production Res. Lab., USDA-ARS, P.O. Drawer 10, Bushland, TX 79012,
Soil & Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843

^* Corresponding author.

Nitrogen availability is important for rapid establishment of small seeded legumes and is influenced by soil N status and rapid development of N₂ fixation activity. Seedlings of arrowleaf clover (Trifolium vesiculosum L. Savi) are exposed to soil temperatures (10–35°C) during the fall which can reduce seedling vigor by influencing N nutrition. Root temperature (18,25, or 32 °C) effects on N nutrition of arrowleaf clover receiving starter N was evaluated in two controlled experiments. Temperature influenced the N status of inoculated plants througli an effect on N₂ fixation but not on starter N uptake. Growth and N₂ fixation were best at 25 °C where effectiveness of two strains of Rhizobium leguminosarum bv. trifolii was similar, but, at 32 °C, strain RP115-2 was less effective than strain 162x68. Addition of mineral 14 (0.5 and 1.0 mg N plant^–1) improved growth and stimulated N₂ fixation at 25 °C more than at 18 or 32 °C. Time required for nodulation was also influenced by N and temperature but was not different between the two strains of Rhizobium. Nodules were first visible 6.4 tn 8 d following inoculation at 25°C, but required 8.0 to 11.3 d at 18 or 32°C with the longer period occurring for plants receiving 1.0 mg N plant^–1. Growth of control plants receiving adequate mineral N showed little influence of the root temperature regimes. Root temperatures influenced early growth of arrowleaf clover through an effect on N₂ fixation and root temperatures of 32 °C or greater were particularly detrimental because of combined effects of delayed modulation and reduced N₂ fixation activity.

Received for publication August 22, 1991.