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

2.8. Field experiments
The greenhouse experimental design and treatments were replicated in the field. The
experiments were carried out during the LR season of 1999 (April–June) and SR
season of 1999/2000 (October–January). Land preparation was done by a disc plough
followed by disc harrowing. A basal dose triple superphosphate (TSP) fertilizer
was applied at the rate of 40 kg ha –1 on all the plots to alleviate phosphorus deficiency.
The crop was dry planted on 1st of April and 31st October 1999 during
the two seasons, respectively. Each experimental replicate constituted a 3 × 3 m plot.
Tepary beans were sown in rows 50 cm apart with spacing of 20 cm giving a plant
density of 100,000 plants ha –1 . This is the recommended density for TB in these
semi-arid areas of SE-Kenya (Shisanya, 1998). Undamaged seeds of uniform colour
and size were selected for the experiments. Before planting, inoculation with the
respective rhizobia was carried out by adding gum Arabica sticker material to the
filter mud carrier (Kibunja, 1984). They were thoroughly mixed with tepary bean
seeds and a little water added. For each of the treatments 3 seeds were planted
per hole. During the first weeding (7 days after planting (DAE)) plants were
thinned to two per hole. At 10 DAE, when the plants were about 20 cm above
ground, calcium ammonium nitrate (CAN) powder (26% N) was top-dressed on
N treatment plots at the rate of 40 kg ha –1 .
Plants were sampled at 21 DAE, 42 DAE and at physiological maturity (70 DAE).
Four plants were randomly sampled from each treatment replicated and various parameters
assessed. The plants were dug up for nodule counting and determination
of below and above ground biomass. Plant samples and nodules were dried to
constant weight at 70 °C in an oven. Dry weights were determined using a high
precision Sartorius balance. Average plot yield per treatment was used to calculate
yield ha –1 . All data were subjected to ANOVA using the statistical computer
package STATGRAPHICS and treatment means separated using Duncan’s multiple
range test at P ≤ 0.05 level (Steel and Torrie, 1981).
2.9. Results
2.9.1. MPN counts
Improvement of Grain Legume Production in Semi-Arid Kenya 177
The most likely number of Rhizobia specific to TB was calculated from the
MPN results (Table 3), according to the method of Vincent (1970) (see also
Table 3. Nodulated units in tepary bean MPN greenhouse experiment. a
Soil dilution 10 –1 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 10 –8 10 –9 10 –10
No. of tubes
with nodulation 4 4 3 0 0 0 0 0 0 0
a Number of replications (n) = 4; Dilution steps = 10; Lowest dilution = 10 –1 ; number of tubes with
nodulation = 11 (Source: after Shisanya, 2002).