Agriculture Reference
In-Depth Information
TABLE 5.10
Nitrogen Use Ratio (NUR) of Tropical Legume Cover Crops as Influenced by Soil pH Levels
NER (mg mg
−
1
)
Cover Crop Species
High Acidity
Medium Acidity
Low Acidity
Short-flowered crotalaria
41.84abc
33.04abcd
30.58a
Sunnhemp
36.90abc
32.34abcd
37.03a
Smooth crotalaria
30.38c
22.42d
25.38a
Showy crotalaria
30.88c
27.33bcd
28.42a
Crotalaria
28.00c
23.77cd
30.60a
Calapo
36.78abc
40.21abcd
31.46a
Black Jack bean
28.56c
27.94bcd
30.29a
Bicolor pigeon pea
26.86c
25.79bcd
32.23a
Black pigeon pea
33.35c
31.02abcd
35.01a
Mulato pigeon pea
37.29abc
41.62abc
31.72a
Lablab
37.40abc
37.50abcd
32.18a
Mucuna bean ana
56.18ab
47.01a
40.44a
Black mucuna bean
57.00a
48.42a
28.88a
Gray mucuna bean
46.48abc
43.34ab
34.01a
White Jack bean
34.69bc
34.51abcd
24.97a
Brazilian Lucerne
27.43c
33.58abcd
31.48a
Average
36.88
34.36
31.54
F-test
Acidity level (A)
*
Crop species (C)
**
A × C
**
Note:
The acidity treatments were created by applying dolomitic lime at the rate of 0 g kg
−1
(high acidity), 3.3 g kg
−1
(medium acidity), and 8.3 g kg
−1
of soil (low acidity).
*,**Significant at the 5% and 1% probability levels, respectively. Means within the same column followed by the same letter
do not differ significant at the 5% probability level by Tukey's test.
in higher amounts by plants and its translocation to grain is crucial for increasing yields. A relation-
ship was determined between grain yield and NUE of 19 upland rice genotypes tested under two N
rates (zero, low, and high, 400 mg) (Figure 5.3). AE, APE, ARE, and UE had significant positive
associations with grain yield.
Similarly, in a field experiment, NUE of lowland rice genotypes grown in field experiments
had significant positive quadratic association with grain yield (Fageria and Baligar, 2005). López-
Bellido et al. (2003) also reported that NUE in the faba bean was higher in the years with higher
seed yield and higher N uptake. However, plant N accumulation and grain yield generally had posi-
tive quadratic relationships (Fageria and Baligar, 2001; Cassman et al., 2002), which means that
diminishing returns appear in the conversion of plant N to grain as yields approach yield potential
ceilings.
The author studied the relationship between NUEs and dry bean yield (Table 5.11). All the
five NUEs were having highly significant (P < 0.01) association with grain yield (Table 5.11). AE
was having higher coefficient of determination (R
2
= 0.57*), followed by UE (R
2
= 0.47*), APE
(R
2
= 0.37*), ARE (R
2
= 0.34*), and PE (R
2
= 0.27*). Significant positive association between grain
yield and NUEs indicates that improving NUE by using N-efficient crop genotypes along with
improved N management practices can improve grain yield as well as reduce environmental pol-
lution (Wiesler et al., 2001). Good et al. (2004) reported that N fertilization is correlated closely
with crop yields. Farmers tend to use large amounts to maximize the quality and quantity and, so,
