Biological nitrogen fixation, mycorrhizal infection and Azolla symbiosis in two rice cultivars in Egypt.
The effect of biofertilizers (Azolla pinnata, arbscular mycorrhizal fungi. (AMF) and Azospirillum brasilense) was examined on growth, grain yield, biological nitrogen fixation and nutrient uptake by 2 rice cultivars (Oryza sativa cultivars Giza 172 and IR 28) grown in Egypt. The grain produced from the inoculated treatments was more than from the uninoculated controls. Similar trends were observed with N, P and K uptake by both rice cultivars. The relative increases in grain yield of the inoculated plants over the control in the 2 cultivars may reflect the fact that Giza 172 is a better host to the inocula than JR 28. Regarding the proportions of N derived from air, significant percentages and values of this occurred with the incorporation of Azolla, either individually or in combination with other inocula. The treatments that increased the proportions of N derived from fertilizer (Ndff), i.e. AMF, mostly tended to reduce those derived from air (Ndfa) and vice versa. The varietal difference between the two rice cultivars could not be easily distinguished as far as their response to N2- fixation was concerned. Azolla and its combinations had less Ndff and higher Ndfa, while Azospirillum or AMF had higher Ndff and less Ndfa. 15N recovery percentages confirmed that AMF was the most effective inoculum for enhancing soil and/or fertilizer N uptake by rice cultivars, while Azolla was the best agent for transferring fixed N to rice plants.