Agriculture Reference
In-Depth Information
TABLE 7.11
Maximal Root Length of 10 Tropical Cover Crops as Influenced by N and Bradyrhizobial
Inoculants
Maximal Root Length (cm)
Cover Crops
N
0
N
1
N
2
N
3
Average
1. Crotalaria
29.00ab
24.00cde
24.67cd
20.67e
24.58b
2. Smooth crotalaria
33.00a
25.33bcd
30.67ab
28.67abc
29.42a
3. Showy crotalaria
22.00d
21.67de
29.33bc
26.33cd
24.83b
4. Calopo
27.67bc
29.33ab
34.00ab
32.33ab
30.83a
5. Pueraria
23.33cd
24.33cde
24.00d
28.00bc
24.92b
6. Pigeon pea
30.00ab
30.67a
34.33a
23.00de
29.50a
7. Lablab
26.67bcd
29.33ab
31.67ab
26.33cd
28.50a
8. Black velvet bean
25.33bcd
20.00e
18.33e
32.33ab
24.00b
9. Gray velvet bean
27.67bc
29.33ab
30.67ab
33.33a
30.25a
10. Jack bean
23.67cd
27.67abc
21.00de
20.00e
23.08b
Average
26.17a
26.83a
27.87a
27.87a
26.99
F-test
N rate (N)
NS
Cover crops (C)
**
**
N × C
CVN (%)
9.27
CVC (%)
6.75
Source:
Adapted from Fageria, N. K. (In press).
Commun. Soil Sci. Plant Anal
.
**, NS: Significant at the 1% probability level and not significant, respectively. Means in the same column followed by the
same letter are not significantly different at the 5% probability level by Tukey's test. Average values were compared in the
same line for significant differences among N rates. N
0
= 0 mg N kg
−1
; N
1
= 0 mg N kg
−1
+ Bradyrhizobial inoculants; N
2
=
100 mg N kg
−1
+ Bradyrhizobial inoculants; and N
3
= 200 mg N kg
−1
.
treatments, the minimal root length of 23.08 cm was produced by the jack bean and maximal root
length of 30.83 cm was produced by calopo, with an average value of 26.99 cm. Variation in the root
length is genetically controlled and varied among plant species and it is also influenced by environ-
mental factors (Eghball et al., 1993; Costa et al., 2002; Fageria et al., 2006).
The root dry weight had a significant N × cover crop species interaction (Table 7.12), indicating
a variation in the root dry weight with the variation in N and Bradyrhizobial inoculants. In control
treatment (N
0
), the shoot dry weight varied from 0.16 g plant
−1
produced by pueraria to 2.01 g plant
−1
produced by the gray velvet bean, with an average value of 0.72 g plant
−1
. These two cover crops
also produced minimal and maximal root dry weights at the N
1
(0 mg N kg
−1
+ inoculants) and N
2
(100 mg N kg
−1
+ inoculant) treatments. However, at the N
3
(200 mg N kg
−1
) treatment, the minimum
root dry weight was produced by crotalaria and the maximum root dry weight was produced by the
black velvet bean. Across four N levels, the minimum root dry weight was produced by crotalaria
and pueraria and the maximum root dry weight was produced by the gray velvet bean. Overall,
the gray velvet bean produced about a 12-fold more root dry weight compared with the minimum
root dry weight-producing cover crops such as crotalaria and pueraria. The root dry weight is an
important trait in improving the organic matter content of the soil as well as in the absorption of
water and nutrient (Sainju et al., 1998; Fageria et al., 2006). Vigorous root system also assimilates
large amount of leachable nutrients from soil profile such as N and such nutrients are absorbed by
the succeeding crops (Kristensen and Thorup-Kristensen, 2004; Fageria et al., 2011). The root dry
weight was having a significant positive association with the shoot dry weight (Figure 7.9). Figures
