Al. Smit et al., THE SPATIAL AND TEMPORAL ROOTING PATTERN OF BRUSSELS-SPROUTS AND LEEKS, Netherlands journal of agricultural science, 44(1), 1996, pp. 57-72
The vegetables Brussels sprouts (Brassica oleracea L. var gemmifera) a
nd leeks (Allium porrum L.) differ widely in the degree of nitrogen ut
ilisation under field conditions. Brussels sprouts usually take up nit
rogen in a relative short period after planting and leaves a profile d
epleted of nitrogen. Leeks, however, utilise in general only half of t
he available nitrogen. This implies that for this crop large amounts o
f nitrogen can be subject to losses to the environment during or after
the growing period. In order to investigate the role of the root syst
em in nitrogen utilisation, rooting intensity and distribution of the
two crops were assessed in field experiments and in the Wageningen Rhi
zolab, a rhizotron facility built in 1990. In field experiments rootin
g was quantified in the various layers of the profile as the volumetri
c Root Length Density (RLD, cm cm(-3)) and in the Rhizolab with horizo
ntal glass minirhizotrons as the Number of Roots per cm(2) (NR). A reg
ression procedure of RLD and NR on thermal time (accumulated average d
aily temperature above ground) after planting revealed that the rootin
g depth of Brussels sprouts increased faster with thermal time than ro
oting depth of leeks, e.g. in one of the experiments in the Rhizolab 0
.13 cm (degrees C day)(-1) and 0.08 cm (degrees C day)(-1) respectivel
y. Furthermore, leeks showed an unusual distribution of roots in the p
rofile with maximal rooting intensity at depths of 10-20 cm. In all ex
periments the proliferation of roots (calculated as the increase in NR
or RLD with thermal time) was slower in leeks than in Brussels sprout
s, especially in the deeper layers of the soil profile. Therefore leek
s can be considered as a shallow rooting crop. Compared to the Rhizola
b, the field experiments showed in general the same difference between
the crops: for Brussels sprouts a higher root density, a deeper rooti
ng and a faster proliferation of roots. For both crops, however. the p
roliferation of roots at the deeper layers was in the field much slowe
r, probably due to unfavourable conditions in the subsoil caused by hi
gher bulk densities or temporary high water tables. The consequences o
f different rooting patterns for nitrogen utilisation are discussed.