Agriculture Reference
In-Depth Information
a significantly positive relationship with grain yield (Y = −10.52 + 2.08X - 0.058X
2
, R
2
= 0.42*).
The positive association between straw yield and grain yield of lowland rice has been reported by
Fageria and Barbosa Filho (2001), Fageria et al. (2008), Fageria et al. (2009), and Fageria et al.
(20 011b).
Grain yield increased in a linear fashion with the addition of N in the form of ammonium sulfate
and in a quadratic fashion with the addition of N in the form of common urea and polymer-coated
urea (Table 3.16). Based on a regression equation, maximum grain yield was obtained with the
addition of 340 mg N kg
−1
by common urea and 203 mg N kg
−1
by polymer-coated urea. Among
the three N sources, the highest grain yield was obtained with the addition of ammonium sulfate at
the three N rates. However, at the intermediate N rate (200 mg N kg
−1
), three N sources produced
an almost equal grain yield. At the highest N rate of ammonium sulfate, the increase in grain yield
was about 10 times compared to control treatments. Fageria et al. (2011b) reported that, at a lower as
well at a higher N rate, ammonium sulfate produced a higher grain yield in upland rice compared to
urea fertilizer under greenhouse conditions. Similarly, Fageria et al. (2010b) also reported a higher
grain yield of lowland rice in a field experiment compared to urea fertilization. The higher yield of
rice with ammonium sulfate may be related to the higher acidity produced by this fertilizer in the
rhizosphere because rice is an acid-tolerant plant (Fageria, 2014). The higher acidity might have
favored balanced nutrition for rice plants due to the acidity tolerance characteristics that may be
responsible for higher grain yield.
Panicle density was significantly increased with the addition of N fertilizer with the three nitro-
gen sources. However, values varied from source to source and from rate to rate. Panicle density
increased in a quadratic fashion with the increasing N rate in the range of 0-400 mg kg
−1
from three
N sources (Table 3.16). The variation in panicle density with the addition of N was 55% by ammo-
nium sulfate, 66% by common urea, and 78% by polymer-coated urea. Maximum panicle density
was obtained with the addition of ammonium sulfate at a lower as well as at a higher N rate. This
might be one of the factors responsible for the higher grain yield with ammonium sulfate compared
to two other sources, since panicle density was having a significant exponential quadratic rela-
tionship with grain yield (Y = 0.22 exp(1.14X - 0.082X
2
), R
2
= 0.73*). Fageria and Barbosa Filho
(2001), Fageria et al. (2001), and Fageria et al. (20011a) reported a significant positive association
between panicle density and grain yield of lowland rice. Fageria et al. (2011a) also reported that
ammonium sulfate produced a higher panicle density compared to urea in lowland rice grown on
Brazilian Inceptisol. Figures 3.33 through 3.35 show the growth of lowland rice with the addition of
N from three different sources of nitrogen.
The author also conducted another greenhouse experiment to evaluate the response of lowland
rice genotypes to N fertilization (Table 3.17). Grain yield was significantly (P < 0.01) influenced by
N rate, genotype, and N × genotype interaction. A significant N × G interaction indicates different
responses of genotypes to N rates. Grain yield varied from 9.12 g plant
−1
produced by genotype
BRA 051135 to 15.16 g plant
−1
produced by genotype BRS Jaçanã, with an average value of 12.92 at
a low N rate. Similarly, at a high N rate, grain yield varied from 17.05 g plant
−1
produced by geno-
type BRA 051135 to 24.43 g plant
−1
produced by genotype BRS Tropical, with an average value of
20.91 g plant
−1
. The increase in grain yield at a high N rate was 67% compared with a low N rate. An
increase in grain yield of lowland rice with the addition of N fertilizer has been reported by Fageria
and Barbosa Filho (2001) under greenhouse conditions.
Panicle density varied from 5.00 per plant produced by genotype BRA 051134 to 8.08 per plant
produced by genotype BRA 051083, with an average value of 6.58 at a low N rate. At a high N rate,
panicle density varied from 10.00 per plant produced by genotypes BRA 051134 and BRA 051135,
with an average value of 12.85 per plant. The increase in panicle density was almost double at a high
N rate compared with a low N rate. The panicle density or panicle number was significantly and
linearly related with grain yield (Y = 4.6694 + 1.2607X, R
2
= 0.9350*). Fageria and Barbosa Filho
(2001) reported a highly significant correlation (r = 96*) between grain yield and panicle density in
lowland rice grown in Brazilian Inceptisol.
