Production Practices and Quality Assessment of Food Crops. Vol. 1

182 Chris A. Shisanya
Table 11. N concentration at harvest in TB plant tissues during the LR season 1999 and SR season
of 1999/2000.
Treatment LR season 1999 SR season 1999/2000
Shoot Root Seed Shoot Root Seed
———————— N concentration (mg N/g dry matter) ————————
TB+N* 1.5 b 0.6 b 2.5 b 1.5 b 0.8 b 2.5 b
Control 1.1 b 0.5 b 2.0 b 1.3 b 0.6 b 2.0 b
TB + R3254 2.3 a 1.8 a 3.8 a 2.1 a 2.0 a 3.8 a
TB + R446 1.7 b 0.8 b 2.9 b 1.5 b 0.9 b 2.8 b
TB + RTB 1.6 b 0.6 b 2.8 b 1.5 b 0.8 b 2.9 b
TB + R578 1.3 b 0.7 b 2.3 b 1.4 b 0.7 b 2.5 b
TB + R579 1.5 b 0.8 b 2.4 b 1.5 b 0.9 b 2.3 b
Means (n = 4) followed by the same letter down the column are not statistically different (P ≤ 0.05)
by Duncan’s multiple range test.
* Nitrogen (N) fertilizer was top-dressed 10 DAE at the rate of 40 kg ha –1 of CAN (26% N) powder.
above the threshold (50 rhizobia cells per gram of soil) at which inoculation may
be excluded (Thies et al., 1991). The soils were collected during the dry season
and it is also expected that during the rains rhizobia along with other soil microorganisms,
Rhizobia population number would increase (Gitonga et al., 1999; Maingi
et al., 2001). These results support the findings of Nambiar et al. (1983) that most
tropical soils have rhizobial population of at least 100 rhizobia cells per gram of soil
capable of nodulating the legumes grown in such soil.
The number of nodules on the tepary bean in all the treatments was counted
regardless of their size. The greenhouse results (Table 4) obtained on nodulation
indicated that tepary bean inoculated with Rhizobium strains R3254, RTB and
R446 had good nodulation, while those inoculated with strains R578, R579 and N
treatment had poor nodulation. There was no nodulation in the control treatment.
Overall, treatment R3254 had significantly higher (P ≤ 0.05) nodule number than
the other treatments (Table 4). These nodules were effective in N 2 fixation as
evidenced by the pink colouration of the nodules indicating the presence of
leghaemoglobin (Sprent and Sprent, 1990; Amara et al., 1995;). Nodule number is
always used as a measure of infectiveness (Beck et al., 1993). The high number
of nodules per plant in tepary bean inoculated with strain R3254 was evidence for
the high infectiveness of this particular Rhizobium strain.
The plant test is the only confirmatory test for rhizobia (Vincent, 1970). Glass
growth tubes were used for plant tests. This method, besides the Leonard jar
assembly, has become a standard method for testing nodulation and nitrogen fixation
under greenhouse conditions (Beck et al., 1993). The method is economical in water
use and reduces the chances of bacterial contamination (Beck et al., 1993). The tubes
occupy very little space in the greenhouse and provide good depth for growth and
development of roots. Nitrogen production due to algae growth on media and in
water has been shown to be minimal (Hornetz et al., 2000). Plant dry weight was
used indirectly to estimate N 2 fixation in the present study. This method is the