بررسي تثبيت نيتروژن و گره زايي سه رقم يونجه يكساله در دماهاي مختلف منطقه ريشه و دماي پايين هوا

Nitrogen fixation and nodoulation of three annual Medicago specie at different root zone temperatures under low air temperature

Air and root zone temperatures are important factors for nitrogen fixation of legumes. Annual medic requires temperatures in the range of 20 to 25 for optimal symbiotic activity. When soil temperature drops below this range, legume nodulation and N fixation are negatively affected. Thus nitrogen fixation and nodulation were studied in an experiment with three annual medics under low air and different root zone temperatures. The plants were grown in growth chamber with 15110°C day/night air temperature during experimental period. Three species of annual medics namely Medicago polymorpha, M. radiata, and M. rigidula that suppose to be adapted with cold and temperate zones were used. Root zone temperatures at four levels including 5, 10, 15 and 20°C were considered. The experimental plan was factorial in a complete block design with three replications. Result showed that the annual Medicago species had significant difference for nitrogen fixation and nodulation. M. rigidula had more nodule dry matter, root dry matter, nodule number, nodule colon number, nodule number in each colon, nodule length, nodule dispersion in root length, plant protein and nitrogen percent than M. radiata and M. Polymorpha. Thus M. rigidula may be better for ley- farming system in cold and temperate zones. When the root zone temperature was 5°C both nodulation and nitrogen fixation were inhibited. However the highest nitrogen fixation and nodulation occurred at 20°C root zone temperature. Root zone temperatures, below 20°C decreased all above mentioned traits. In conclusion, application of ley- farming system is not successful in zone that soil temperature is lower than 5°C especially for nitrogen fixation and nodulation. Thus, in zones that soil temperature is more than 10°C, annual medics have normal growth and symbiotic activity.