Leek and shallot 369
grown in a Mitscherlich pot containing 8 kg sand. Leaves and bulbs were sampled
twice during the growth period to follow up translocation processes. The first sampling
was carried out when leaves were developed, but bulb growth had not yet started and
the second one during main bulb growth. An increasing S supply was related to an
increasing alliin content in leaves and bulbs of both crops, whereas nitrogen fertilization
had only a minor influence. The alliin content in bulbs could be doubled by S
fertilization. A translocation of alliin from leaves to bulbs was found so that time of
harvest has a strong influence on the alliin content. At the beginning of plant development
high alliin contents were found in leaves, while with bulb development they were
translocated into this plant organ. The results show that the potential health benefits
of Allium species could be distinctly improved by S fertilization.
Brunsgaard et al. (1997) stated that leeks were cultivated under conditions differing
in level of N supply (100, 160, 220 or 280 kg/ha), level of water supply (normal or
low) and time of harvest (September, October or November). The protein content of
the leeks increased progressively from 90 to 163 g/kg DM with N supply. This
increase in protein was associated with a reduction of all essential amino acids (g/16g
N: lysine 5.60, methionine 1.42 and threonine 3.40) and subsequently, a significant
reduction of the biological value. Protein and energy digestibilities increased with
level of N supply. Leeks harvested in September (protein 160 g/kg DM, biological
value 82.8%) had a higher (P < 0.05) protein content, but had at the same time the
lowest (P < 0.05) biological value as compared to leeks harvested in October (protein
128 g/kg DM, biological value 89.7%) or November (protein 125 g/kg DM, biological
value 90.5%). This was due to a lower content of essential amino acids (g/16g N) in
leeks harvested in September as compared to leeks of later harvest. Only small
differences between the two levels of water supply were observed in the composition
of the leeks. The content of non-starch polysaccharides (NSP) was high in all samples
of leek (approximately 240–280 g/kg DM) and appeared to be unaffected by the
growth conditions applied in the investigation. Soluble NSP constituted approximately
half of the total NSP.
Effect of method of growing and age of seedling on chemical composition
Kunicki (1993) reported that in a three-year trial, leek cultivar Argenta transplants
11, 13 or 15 weeks old were planted in a mid-July after an early potato crop at a depth
of 6, 12, or 18 cm and spacing of 40 ¥ 15 cm. The length and time for which the field
was used for these two crops amounted to an average of 212 days. The marketable
yield of leeks grown as an aftercrop was 17.1–33.6 t/ha. Transplant age had no effect
on the crop height or quality. With increasing depth of planting, the pseudostem and
its blanched part increased in length, but the DM and vitamin C (ascorbic acid)
contents decreased.
Kaniszewski et al. (1989) reported that in field experiments conducted from 1985
to 1987, the effects of four growing methods, viz. (i) traditional planting at a depth
of 5 cm, (ii) planting as above followed by earthing-up, (iii) planting into 15 cm deep
furrows, levelled during the growing season, and (iv) planting into 20 cm deep holes,
were investigated using the cultivars Alaska, Darkal, Jolant and Nebraska. Planting
into 20 cm deep holes reduced the yield, compared with the other three treatments
which gave similar yields. Earthing-up, planting into furrows or into 20 cm deep
holes increased the length and weight of the blanched part of the shaft, compared
with traditional planting. Laboratory trials showed that blanched shafts contained
more DM and total sugars, and less vitamin C, reducing sugars and nitrates than