Agriculture Reference
In-Depth Information
A very strong association, following an exponential function, between the LAI and the propor-
tion of radiation intercepted by corn plants is documented in the scientific literature (Hipps et al.,
1983; Trapani et al., 1992). Following these fundamental principles, a critical LAI threshold (close
to 4.0 m
2
m
−2
) was defined after which further increase in LAI is not reflected in the increase in the
production of the radiation intercepted by corn (Maddonni and Otegui, 1996). Costa et al. (2002a)
reported that genetically altering corn to increase the leaf number per plant could increase grain
yield under short season conditions. These authors further reported that alterations resulting in leaf
arrangements that maximize light interception and optimize RUE could further improve yield.
1.2.1.8 Root Growth
Nitrogen improves the root growth of cereals and legumes (Fageria and Moreira, 2011; Fageria,
2013). Root morphology is influenced by the amount of N fertilizer applied (Eghball et al., 1993).
Eghball et al. (1993) showed that N stress in corn reduced root branching. Similarly, Maizlish et al.
(1980) showed greater root branching in corn with increasing levels of applied fertilizer N. Costa
et al. (2002b) reported that greater root length and root surface area were obtained at an N fertilizer
rate of 128 kg N ha
−1
compared with either the absence of fertilizer N or the higher rate of 255 kg N
ha
−1
. N fertilizer improves root growth in soils having low organic matter content (Gregory, 1994;
Robinson et al., 1994). N fertilization may increase the crop root growth by increasing soil N avail-
ability (Weston and Zandstra, 1989; Garton and Widders, 1990). Sainju et al. (2001) observed that
tomato (
Lycopersicon esculentum
Mill.) root growth was greater with hairy vetch and crimson
clover cover crops and 90 kg N ha
−1
than with no cover crops or N fertilization. N also improves the
production of lateral roots and root hairs, as well as increasing rooting depth and root length density
deep in the profile (Hansson and Andren, 1987). Hoad et al. (2001) reported that surface application
of N fertilizer increases root densities in the surface layers of the soil.
N fertilization can increase the root length and root surface area and decrease root mass per unit
area of corn (Anderson, 1987; Costa et al., 2002b). It is well known that roots tend to proliferate in
nutrient-enriched soil zones (Drew et al., 1973; Qin et al., 2005). Russell (1977) refers to this as a
compensatory response. The results of pot experiments showed that corn roots were longer and thin-
ner in zones that were rich in N (Zhang and Barber, 1992, 1993; Durieux et al., 1994). Figures 1.14
and 1.15 show the root growth of two upland rice genotypes at two N levels. The root growth was
much better with the addition of 300 mg N kg
−1
soil as compared to control treatment.
FIGURE 1.14
Root growth of upland rice genotype BRA 032051 without and with N (300 mg N kg
−1
). Half
of the N was applied at sowing and the remaining half at 45 days after sowing.
