Agriculture Reference
In-Depth Information
7.6.10 a
GrICultural
C
hemICals
In modern agriculture, the use of herbicides, fungicides, and insecticides is fundamental to control
weeds, diseases, and insects. Graham (1981) reported that herbicides and insecticides applied at the
recommended rates do little damage to nodulation or to
Rhizobium
in soil. Similarly, Gibson (1977)
reported that herbicides at normal application rates have little, if any, effect on free-living rhizobia,
but a number of reports indicate that they may interfere with nodulation. Gibson and Jordan (1983)
reported that herbicides and insecticides generally have little effect on the viability of rhizobia.
However, Gibson (1977) reported that the effect of herbicide on nodulation depends on the herbicide
and also on the legume species. Many herbicides affect root development or chlorophyll synthesis
and it is not surprising that they may influence nodule formation and function (Gibson, 1977).
Strains of rhizobia vary in their response to different fungicides and it has been suggested that the
selection of a fungicide-resistant mutant may provide inoculant strains with a competitive advantage
in field situations (Gibson and Jordan, 1983).
7.6.11 C
rop
s
peCIes
and
G
enotYpes
wIthIn
s
peCIes
There is a significant difference in dinitrogen fixation among crop species and genotypes within
species. For example, soybean in the Brazilian Cerrado region (central part) produced a good yield
(>4000 kg ha
−1
) when seeds were inoculated with appropriate rhizobium. However, dry bean could
not produce maximum grain yield without the application of the chemical form of N. The author
and collaborators conducted greenhouse and field experiments testing promising dry bean geno-
types using rhizobia and N treatments. Under greenhouse conditions, shoot and grain yield was
significantly influenced by N and genotype treatments and N × genotype interactions were also
significant for these two traits (Tables 7.4 and 7.5).
The N × G interaction indicates that responses of dry bean genotypes differ in the shoot dry
weight and grain yield with the variation in N treatments (Table 7.4). The shoot dry weight at
N
0
treatment varied from 3.26 to 10.47 g plant
−1
, with an average value of 6.48 g plant
−1
. At N
1
treatment, the variation in the shoot dry weight was from 4.45 to 10.92 g plant
−1
, with an average
value of 7.55 g plant
−1
. Similarly, at N
2
treatment, the variation in the shoot dry weight was twofold
between the lowest and highest shoot dry weight-producing genotypes. At N
3
treatment and across
the four N levels, the minimum shoot dry weight was produced by the genotype BRSMG Talisma
and the maximum shoot dry weight was produced by the genotype Diamente Negro. Overall, the
maximum shoot dry weight was produced at the N
3
rate (200 mg N kg
−1
) and the minimum shoot
dry weight at the N
2
rate (inoculation with rhizobial strains + 50 mg N kg
−1
). Overall, an increase
in the shoot dry weight with the inoculation of dry bean genotypes with rhizobium strains was 16%
and at 200 mg N kg
−1
the increase in the shoot dry weight was 25% compared to control treatment.
Variations in the shoot dry weight among dry bean genotypes have been reported by Fageria et al.
(2011). These authors also reported the response of dry bean genotypes to N fertilization.
The grain yield of dry bean genotypes varied significantly by N and genotype treatments and
the N × G interaction was also significant (Table 7.5). Across four N treatments, the minimum
grain yield was produced by the genotype BRSMG Talisma and the maximum grain yield was
produced by the genotype Diamante Negro. When the average values of N treatments were com-
pared, the maximum grain yield was obtained with the addition of 200 mg N kg
−1
soil and mini-
mum grain yield with the treatment inoculation + 50 mg N kg
−1
soil. The increase in grain yield
with the inoculation of dry bean seeds with rhizobial strains was 7% compared to control treat-
ment. The average increase in grain yield with the addition of 200 mg N kg
−1
was 27% compared
to 0 mg N kg
−1
or control treatment. Overall, there was a significant decrease with the application
of 50 mg N kg
−1
+ inoculation. Hence, there was a negative interaction between rhizobium and N
application in small amounts. The grain yield results clearly show that dry bean genotypes did not
