Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

178j 9 Rice–Rhizobia Association: Evolution of an Alternate Niche
rhizobia in gnotobiotic plant bioassays; there is high strain–variety specificity in
rhizobial promotion of wheat growth.
Several field inoculation trials have been conducted to assess the agronomic
potential of these Rhizobium–cereal associations under field conditions, with the
long-term goal of identifying, developing and implementing superior biofertilizer
inoculants that can promote rice and wheat productivity in real-world cropping
systems while reducing their dependence on nitrogen fertilizer inputs. A direct
agronomic approach was adopted to address the importance of continued evaluation
of the various strain genotypes in our diverse collections of cereal-adapted rhizobia
under experimental field conditions [1,7]. This meant first acquiring useful information
from laboratory PGP bioassays. This information was then applied to design
and implement small field trials at the Sakha Agricultural Research Station in the
Kafr El-Sheikh area of the Nile delta, Egypt. Information from these results was then
utilized to conduct scaled-up experiments on large farmers fields in neighboring
areas of the Nile delta where cereal–legume rotations are used, so our results could
be compared to real on-farm baselines in grain production.
Experiments included nitrogen fertilizer applications at three rates: one third, two
third and the full recommended rate previously assessed without inoculation with
nitrogen fixer(s). The inocula for rice and wheat were used as indicated in Tables 9.1
and 9.2. The field trials were conducted in 20-m 2 subplots or sub-subplots with four
replications. The various trials were supplemented with calcium superphosphate
before tillage, with potassium sulfate added 1 month after wheat sowing or rice
transplantation. Appropriate broad-spectrum herbicide(s) were applied to control
the major narrow- and broadleaf weeds.
In total, we conducted 24 different field inoculation trials using selected endophytic
strains of rhizobia with rice and wheat in the Nile delta. So far, positive
Table 9.1 Grain yields of rice variety Giza 178 in the best
experimental treatments versus adjacent farmer’s fields at
different locations in Kafr El-Sheikh, Nile delta, Egypt, 2002.
Farm location
Best experimental
treatment: inoculated
strains þ kg of
nitrogen fertilizer a
Grain yield of best
experimental
treatment (kg ha 1 )
Yield in adjacent field
(no researcher
supervision)
(kg ha 1 ) b
Baltem E11 + E12 + 96 N 8623 8330 3.5
Beila E11 + E12 + 96 N 11 309 9520 18.8
Metobas E11 + E12 + 96 N 12 400 9520 30.3
Sidi Salem 144 N 11 118 9068 22.6
Increase over
farmer’s yield
(%)
Source: Dazzo and Yanni [59].
a The method of inoculation was direct broadcast of the inoculum (10 9 CFU g 1 ) at the rate of
720 g peat-based inoculum per hectare, 3 days after transplanting of the rice seedlings and
during a period of calm wind at sunset. Nitrogen, kg N ha 1 , was applied as urea (46% N) in two
equal doses, 15 days after transplanting and at the mid-tillering stage.
b Recommended rate of nitrogen fertilizer for the tested rice varieties when used without
inoculation with biofertilizers is 144 kg N ha 1 . This rate was used by the farmer in the adjacent
field who was not supervised by the research personnel.