Agriculture Reference
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(2012) reported that the application of 180 kg N ha −1 in split application (half at sowing and the
remaining half at the V6 stage—six-leaf stage) is a successful and sustainable management strategy
for corn production in rainfed mountainous ecosystems. A significant linear and quadratic increase
in the yield of corn hybrids has been reported by Costa et al. (2002). The quadratic equation was
(GY = 8654.03 + 44.49N - 0.14N 2 , R 2 = 0.85). Based on a regression equation, the maximum grain
yield was obtained with the application of 156 kg N ha −1 . This rate is within the local limits (Ottawa
region) recommended for the Canadian corn range of 120-170 kg N ha −1 (Costa et al., 2002). Both
linear (Oberle and Keeney, 1990) and quadratic (Oberle and Keeney, 1990; Stecker et  al., 1995)
models have been reported for N fertilization versus grain yield relationships for conventional corn
hybrids.
The author also studied the response of four upland rice genotypes to nitrogen fertilization.
There was a significant quadratic increase in grain yield of all the four genotypes (Figure 3.39).
However, the magnitude of response varied. Yue et  al. (2012b) reported that the average winter
wheat yield was 7.2 Mg ha −1 with the addition of 130 kg N ha −1 in China. The N application tim-
ing was 55 kg ha −1 at sowing and the remaining 75 kg N ha −1 was topdressed at the stem elongation
stage. Berzsenyi and Tokatlidis (2012) reported that in corn maximum grain yield was obtained with
the application of 200 kg N ha −1 . Two-thirds of this N was applied at sowing and the remaining as
topdressed. Similarly, Blumenthal et al. (2003) also reported that maximum corn yield was obtained
with the addition of 2002 kg N ha −1 . Boomsma et al. (2009) did not find significant differences in the
grain yield of corn with N rates ranging from 165 to 330 kg ha −1 . Sindelar et al. (2012) determined
the optimum rate of N for corn, which ranged from 168 to 233 kg N ha −1 depending on the locations.
Half of the N was applied at sowing and the remaining half as topdressed when corn plants were
20-30 cm tall.
Studies of dryland wheat production in the western Prairies of Canada have demonstrated that
grain yield is optimized within the range of 40-90 kg N ha −1 (Beres et al., 2008, 2012a,b; Karamanos
et al., 2005; Selles and Zentner, 1993). Irrigated production would increase supplemental N require-
ments to at least 75 kg N ha −1 (Beres et al., 2008), and as high as 180 kg N ha −1 (Mckenzie et al.,
2008).
The author determined the soil acidity indices of a Brazilian Oxisol under different liming treat-
ments after harvest of three soybean crops. Analysis of variance showed that the year × lime rate
interactions were significant for all the soil chemical properties analyzed (Table 3.18.). Hence, 3
year values of these chemical properties are presented (Table 3.18). In the first year, pH increases
from 5.3 to 7.3 with a lime rate of 0-18 Mg ha −1 . In the second year, the pH increase was 5.2-7.2
in the same lime rate range, and in the third year, the increase in pH was 4.7-7.7. Overall, the pH
6000
5000
4000
3000
2000
BRA 032033 (Y) = 3062.36 + 33.71X - 0.12X 2
R 2 = 0.44*
R 2 = 0.50*
R 2 = 0.41*
R 2 = 0.39*
BRA 042094 (Y) = 2954.10 + 39.76X - 0.17X 2
BRA 01506 (Y) = 2742.31 + 36.55X - 0.17X 2
BRA 032051 (Y) = 1779.37 + 27.12X - 0.13X 2
1000
0
50
100
150
200
Nitrogen rate (kg ha -1 )
FIGURE 3.39
Upland rice genotype responses to nitrogen fertilization.
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