Nitrogen fixation by endophytic bacteria has a potential to contribute to the mitigation of
global warming by reducing the use of nitrogen fertilizer and thus emission of nitrogen oxide.
Screening rice and associated nitrogen fixing endophytic bacteria is limited by a lack of appropriate
N-free nutrient solution. This study set out to evaluate N-free nutrient solutions and systems
for growing rice, by evaluating nutrient solution with 2 different forms of iron (Fe), Fe-citrate
and Fe-EDTA for rice growth and N levels (0 and 70 ppm, N0 and N70). Five rice seedlings
were grown in each pot containing 5 L of either nutrient solution with 2 replications. In one
set of pots the nutrient solution was not renewed and in another set the nutrient solution was
renewed weekly. It was found that chlorophyll content (measured with SPAD502 on the youngest
emerged blade) varied with N levels and form of Fe. The SPAD value of N70 was higher than N0
in both iron forms. Nitrogen deficiency in N0 was indicated by chlorosis and necrosis of older
leaves and greener younger leaves. In N0 without nutrient solution renewal, the SPAD value
was higher with Fe-EDTA than Fe-citrate, with Fe deficiency of Fe-citrate plants indicated by
more chlorosis of younger than older leaves. Rice plants were grown successfully in N0 with
EDTA-Fe in enclosed root system without renewal for one month with 1 L, and longer with 1.5
and 6 L of nutrient solution. The system will now be used for evaluating nitrogen fixation in
rice in association with endophytic bacteria.