In the present study three annual medic cultivars (Medicago polymorpha cv. Santiago, Medicago radiata cv. Radiata and Medicago rigidula cv. Rigidula), were evaluated for symbiosis traits under three levels of day/night air temperatures (DNAT, 15/10, 20/15 and 25/20 ±0.2°C) and four root-zone temperatures (RZT, 5, 10, 15 and 20±0.2°C). The experimental design was a 3x3x4 factorial with treatments organized following a randomized complete block design with three replications. The result showed that low root zone temperature (RZT) and day/night air temperature (DNAT) had a severely reduction effect on root length, root dry matter and nodule formation. Plants did not produce any nodule in the root at 5°C RZT and all DNATs. The plants grown at RZT ranging from 10 to 20°C were found to fix some nitrogen. The 10°C RZT seem to be a thermal critical point for Medicago spp. nodulation and N2 fixation. DNAT also had the same effect on plant nitrogen fixation. This result confirms the possibility to screen medics for growth and nitrogen fixation at low temperature. M. rigidula performs well in nodule formation and nitrogen fixation at low RZT. Therefore M. rigidula is probably the most promising for the production of herbage at low temperature. M. polymorpha was found to have a significant performance in moderate temperatures but was also found to be the most widespread species and thus may be of high priority in cultivar development. The best temperatures for nitrogen fixation and nodule formation for annual medics were 15°C RZT and 25/20°C DNAT.
Khosroo Azizi , Majid Amini Dehaghi and Habib Abbasipour , 2004. Effect of Different Air and Root-zone Temperatures on Nitrogen Fixation and Nodulation of Annual Medics. Journal of Agronomy, 3: 131-136.