Agriculture Reference
In-Depth Information
root. Lateral branches rarely re-branch; as a result, the root length per unit
volume of soil, L
V
, under allium crops is low compared with that of other crop
species. There are only small differences in root morphology between different
onion cultivars, although older Dutch cvs had a slightly higher L
V
than
modern cvs (de Melo, 2003).
However, a comparison of the roots of bunching onion,
A. fistulosum
, with
common onion showed that the former produced 1.29 cm of root per mg of shoot
dry weight as against 0.52 cm/mg for onion
. A. fistulosum
also spread its roots
further from the plant and deeper into the soil. The difference in L
V
is a result of
more fine lateral branches on the main roots of
A. fistulosum
(see Fig. 2.16).
The development pattern of root systems is always variable and can be
influenced by both soil compaction and the distribution of nutrients in the soil.
In one study the root length under an onion crop increased as the crop grew as
described by the equation:
log
e
L = 3.4 + 1.5 log
e
W
0.035T (Eqn 2.1)
where L is the total root length per unit of soil surface (km/m
2
), W is the
crop shoot dry weight (t/ha) and T is days from sowing (Greenwood
et al.
,
1982). Ninety per cent of the root length was found in the top 18 cm of soil
throughout the season, unlike other crops that rooted more deeply as the
Fig. 2.16.
The distribution of root length density (mean length of root per unit
volume of soil (cm/cm
3
) in different root diameter categories in
A. fistulosum
and in
Eastern European and old and modern Dutch onion cultivars (from de Melo, 2003.
Courtesy of Wageningen University, The Netherlands).
